Staying warm this winter: A buyers guide to heating
As autumn declines into another long winter, it seems an opportune time to revisit one of our most popular buyers guides: our essential guide to heating yourself and your home. It can feel like this is an area in which we’re spoiled for choice—but Lance Turner is here to cut through the noise and tell you how to stay toasty.
As the world moves towards a zero-emissions target, it’s become clear that the only way to achieve that goal is to electrify everything, or at least as much as is possible. For homeowners, that means no more burning of fossil gas, especially for heating, which can result in a huge increase in emissions in the cooler months.
Therefore, in this guide, we are not considering gas heating in any form as there is simply no way to run gas appliances without greenhouse gas emissions. The economics of gas heating also do not stack up in almost all cases. See bit.ly/2Hrfebe for Renew’s research report on this subject.
On the other hand, while electricity may be in part generated by coal and other fossil fuels, it doesn’t have to be—you can purchase 100% GreenPower or install a solar power system large enough to cover your needs throughout the year and effectively be greenhouse neutral. Indeed, the average domestic solar energy system is on the order of 9 kW in size—a system of that size can put you considerably in credit both financially and greenhouse gas-wise during the sunnier times, for offsetting the lower generation in the winter months.
The popular options
The two most popular and most energy- efficient fully installed electricity-based heating options are reverse-cycle air conditioning and hydronic heating. There are advantages and disadvantages to both, and either may suit some people, house designs and climates better than others, so which is best for you, and are there other options that should be explored?
When it comes to heating, there are lots of questions to answer, and making the right choices can result in a warm home with low running costs and low environmental impact.
So, what are all of the electric heating options available? Firstly, we will look at the two technologies we have mentioned already, which tend to be used for space (heating the whole room, living space or home) heating— reverse-cycle air conditioning and hydronic heating. Then we will look at some other options, such as resistive electric heaters, convection heaters, some non-electrical options, and take a look at some other heating considerations.
Reverse-cycle air conditioners
Reverse-cycle air conditioners are a form of heat pump, and indeed, many people now refer to them this way, especially for systems installed primarily for heating. Technically, a heat pump is exactly that—it pumps or moves heat from one place to another. Other examples include fridges and freezers, heat pump water heaters, and car air conditioners.
Heat pumps work by compressing a gas, called a refrigerant, which then transfers heat from one place to another. In your fridge, a heat pump transfers heat from inside the cabinet to outside, which is why the outside of the fridge gets warm. In a reverse-cycle air conditioner, the transfer can go either way, hence the name. In winter, heat is taken from outside and dumped inside, and in summer the opposite occurs. See the box “Harvesting heat” for an explanation of where the heat comes from on a cold day.
– A heat pump’s biggest advantage
Reverse-cycle air conditioners are the most efficient form of electric heating commonly available—indeed, their efficiency is usually of the order of several hundred per cent. How is it possible to be more than 100% efficient? Well, we’re glad you asked!
First, let’s look at resistive heating, which use resistive elements to turn the electricity into heat directly (covered later). This form of heating can only ever be at most 100% efficient—the heat output equals the electrical energy input.
Reverse-cycle air conditioners are much more than 100% efficient, in fact, up to 600% efficient, meaning that they use a lot less energy to produce the same amount of heat. How can that be? As mentioned earlier, a heat pump pumps heat from one place to another. Instead of turning energy from one form (electricity) into another (heat), it uses electric energy to move heat from one place to another. Because heat is relatively easy to collect and move, heat pumps can move a lot more heat energy than the equivalent electric energy they use.
The efficiency of heat pumps is given by a coefficient of performance (COP), which is the ratio of the heat moved to the electrical energy input. For example, if your heat pump uses 1 kWh of electricity to move 3 kWh of heat from outdoors to inside your home, then it has a COP of 3. Note that when a system is cooling a home, its cooling efficiency is referred to as its energy efficiency rating (EER)—EER and COP are effectively the same thing, but the efficiency can be different for heating and cooling, and they are therefore specified as separate figures.
Reverse-cycle air conditioners can have a rated COP as high as 6. The actual running COP depends on several factors, including the temperature differential between outdoors and indoors, the refrigerant and compressor type used and overall system design.
Low outdoor temperatures can affect efficiency when heating, with some heat pumps seeing their COPs drop to low levels (less than 2 in some cases) as the ambient temperature approaches 0 °C. If you live in an area that experiences close to freezing winter temperatures, make sure you check the efficiency data if available. This may be supplied as a graph of COP versus ambient temperature for a given output temperature, while some manufacturers just supply COP for several outdoor temperatures.
– The different system types
Reverse-cycle systems come in two main formats—split systems and ducted.
Split systems have the compressor and one set of refrigerant coils in a box outside, often mounted against a wall. The part inside the home is called the air handling unit or indoor unit and consists of the other set of coils, a fan to force air over them and the electronic controls for the system. Multi- head units are a variant, with a single (larger) compressor sized to run multiple indoor air handling units. The outdoor unit and indoor units are linked by flexible or rigid high- pressure hoses or pipes and wiring.
Ducted systems have one or more air handling units that can service a whole house, with conditioned air being ducted to different rooms of the house via insulated ducts. The compressor is still separate but is much larger than the units used for split systems. In some systems it is integrated into the unit with the air handling unit, the whole system mounted outside, usually at ground level.
Split systems are generally the most efficient option, with smaller systems generally being more efficient than larger units. Multi-head splits are less efficient than single-head splits due to a number of factors, not least of which is that the single outdoor unit on a multi-head system must transfer more heat but is unlikely to be twice as large as the outdoor unit for a single head system—a common factor among all manufacturers.
The efficiency of ducted systems is generally lower than split systems due to thermal losses in the ducts and other technical reasons—as mentioned, larger systems generally have lower COPs than smaller systems.
A disadvantage with the single split system approach is that you need an outdoor compressor for every room you want to heat/ cool. This can mean many outdoor units for large homes with many rooms, which can be aesthetically unappealing and take up a lot of outdoor space, at least on sites with a poor house size to block area ratio, where outdoor spaces are narrow and a premium. However, many homes, especially smaller homes, can stay quite comfortable with just two or three units, so this may not be a problem. Plus, a failure in a single unit doesn’t disable heating in several rooms, so there’s an advantage to using separate units as well!
Multi-head and ducted systems get around this problem, but, as already noted, at the cost of reduced efficiency and so lower COP and therefore increased running costs.
Another advantage with split systems (both single and multi-head) is that of zoning, as you’re only heating the rooms or areas occupied at the time. With split systems you have complete control over which ones are running, and you can even select different temperatures for different rooms—great if one occupant feels the cold more than another.
Zoning in ducted systems is done differently, and varies between systems. In the simplest systems, zoning is done by closing off the vents in areas you don’t want heated, but there will be a minimum number of vents that will need to be open for efficient operation. Ducted systems will usually have one or two thermostats located in the zones most likely to be occupied. Rooms further away from the thermostat may not get as warm or respond as well to thermostat setting changes as rapidly as desired. Ducted systems are generally less flexible than multiple splits, although modern ducted systems with electronic controls and more than one thermostat help compensate for this.
Another advantage with split systems is that you can start small, such as heating just one or two of the most used rooms, and add more units as budget permits. With a ducted system, it’s all or nothing, with a large upfront cost and major installation work.
Efficiency of ducted systems can also be greatly impacted through issues such as vermin damage to ducts or ducts coming adrift due to poor installation, or subsequent damage from other tradies. And a failure of the system means the whole house is without heating until it is repaired—with individual splits, the worst you will see is one or two areas unheated.
Split systems are also vastly simpler to install than ducted systems—only a couple of small holes in the wall for piping and cabling between the indoor and outdoor units are needed, and the separation of the two units eliminates leakage of heat from the hot side to the cool side, thus improving system efficiency.
It might seem there’s not much heat outside on a cold day—but that’s just because we are biological creatures evolved to survive in a very narrow temperature band. What we perceive as temperature is ultimately the thermal energy that can be extracted from the environment around us—and there’s plenty of that to go around, even when it feels freezing to us.
Absolute temperature is measured on a scale called the Kelvin scale, which has the same increments as the degrees Celsius scale but starts at absolute zero, where there is no heat whatsoever and all molecular movement ceases.
Absolute zero is the equivalent of -273.15 °C. This means that the freezing point of water, which we’ve set at 0 °C, is 273.15 K, while 25 °C— which we find nice and balmy—is just 298.15 K. In absolute terms, the difference between the two isn’t particularly significant. So while 0 °C might seem cold to us, in reality there is plenty of energy available to harvest for heating your home.
– But how effective are they?
Many people considering a shift to reverse- cycle split systems are concerned as to whether it will keep them as warm as ducted heating or a hydronic system. The biggest perceived negative for using a reverse-cycle system for heating is whether the movement of air has a cooling effect, reducing the effective comfort of the heater. This applies to any form of forced convective heating, but is perhaps exacerbated with some split systems with less than ideal outlet designs which cause relatively high air flow velocities.
This cooling effect may result in occupants setting the heating level higher than they otherwise would to counteract it, increasing energy use. However, there is one, often unconsidered, benefit of this moving air flow—it makes for excellent clothes drying when clothes must be hung up inside. The air handling unit will also remove the extra humidity produced as clothes dry—something most other heating systems don’t do.
Many manufacturers have addressed this issue with wider and/or multiple air outlets with lower air velocities, and directional outlets which allow air to flow down along the walls and floor. The air can also flow across the ceiling for cooling via the Coanda effect, which involves airflow attaching itself to a surface and flowing along it, even if the surface curves away from the airflow.
A minimally restricted path will allow airflows to reach further across a room, more effectively distributing warm (or cool) air. By reducing airflows directly onto occupants by flowing air along surfaces, the undesired cooling effect of moving air when heating the room is reduced. By selecting the correct air handling unit and location for it, you can reduce cold spots or effects.
Many units also feature adjustable airflow patterns for when cooling in summer—the random airflow changes are designed to simulate the natural variations of a cooling breeze.
– Split unit placement
Air handling units are usually wall hung but there are several other types, including floor-mounted (still mounted on the wall, but at floor level), “cassette” types mounted in the ceiling, and even units mounted inside the floor cavity that vent into the room like a floor-mounted duct outlet. If your needs predominantly involve heating, you should consider an air handling unit that is designed to be mounted on, in or near the floor. This allows the heated air to flow across the floor, providing immediate warmth and a higher level of perceived comfort with lower temperature settings. The same applies if you go for a ducted system—in-floor ducts will warm you more quickly than ceiling ducts, although many homes don’t have underfloor cavities for ducting.
The main disadvantage with floor- mounted air handling units is that they generally have a lower overall system efficiency than wall-mounted units of equivalent output rating. It isn’t clear why this should be the case, as the floor-mounted indoor units are at least as large or larger than their wall-mounted cousins, so heat transfer and airflow rates should be at least as good, if not better. We suspect that, because wall- mounted units are by far the most popular, they have been developed further than the other designs for maximum efficiency.
It’s also worth noting that systems using wall-mounted units are cheaper than other types as they are manufactured and sold in much greater numbers.
– How intrusive are they when running?
Most of the noise from split system air conditioners comes from the outdoor unit. The indoor unit is usually very quiet—and is often all but inaudible—in normal use. Noise levels of indoor units range from under 20 dB on low up to 50 dB or so, depending on the system. See bit.ly/3C6hm65.
With ducted systems, meanwhile, the air handling unit is usually located well away from the living areas—either in the ceiling or outside the house—and thus is not really audible.
Outdoor units are noisier because of their compressor and large axial fan, but modern units are much quieter than older units as virtually all modern high-efficiency split systems (and many ducted heat pumps) are of the inverter type. In these types of units, instead of the compressor motor simply being turned on and off, the compressor is controlled by a variable-speed drive or inverter. This allows the compressor to only run as hard as required, and as a result, the system will be much quieter and more efficient, and will also use less electricity.
The harder the unit has to work, the noisier it will be, so don’t buy a system that is barely adequate for your needs as it will be running the compressor fairly hard a lot of the time.
Setting the temperature set-point higher than necessary also means the unit will run harder and more often, and will also waste energy and so cost you more to run.
By the same token, if your house has poor thermal performance, the heat pump will run harder and maker more noise than necessary, wasting money in the process—improving the home’s thermal efficiency can provide many advantages, and should be considered before purchasing a new heating system.
If the noise level generated by an outdoor unit is a problem, that problem can often be mitigated to some extent by smart placement (moving the unit away from bedroom walls, for example) or by surrounding the unit with greenery.
– Other worthwhile features
There is a wide range of features available on reverse-cycle air conditioners. These may include long-life filters (that only need washing every three or six months), air ionisation (to help disinfect the air), high efficiency fan designs to reduce energy use and fan noise, remote controls with timer functions, adjustable airflow patterns, economy modes, infrared sensors to detect when rooms are empty, humidity sensors, wi- fi or bluetooth connectivity for smart home integrations, and many other features, which may or may not be of use to you.
Humidity control can be worth paying extra for if you find that air conditioners dry out the air too much for you. The ideal humidity range for humans is between 40% and 60%. The Daikin US7 systems were designed to maintain that range in the home, however they are no longer available as far as we can tell, and have not found other models with active humidity control, just the usual humidity reduction that is inherent in reverse cycle air conditioner design. If any readers know of split systems with active humidity control like the US7, please let us know!
Another Daikin model that had an interesting feature, the Daikin Nexura, included a radiator panel on the front of the indoor unit. This heated up to emit a low-level warmth similar to a hydronic radiator, so the indoor unit provided both warm air and some radiative heating. However, this model also seems to have been discontinued by Daikin and we are not aware of any other floor- mounted units with a similar feature.
Another useful feature is an inbuilt timer. Almost all units have these now, and they allow you to turn on heating before you wake up, or turn on cooling before you get home from work. Some systems only have one set of timer set-points, so you can’t set different times for different days, such as setting it to turn on later on weekends to allow for sleeping in, or multiple time events in a day. If control flexibility is a requirement, then you should check the details of the timer’s capabilities.
Smart devices that have internet connectivity will also tend to have more flexible control systems, and you may be able to program multiple timers or have the system react to other parameters, such as starting up depending on the indoor temperature. These sorts of capabilities vary widely and can also be enhanced by the use of external controllers and services, so if fine-level adaptability and control is a requirement, you will need to consider a system with smart home compatibility and functionality. [You should also make sure to change the default admin password so your air conditioner doesn’t end up as part of a botnet—Ed.]
You can even upgrade an air conditioner with only basic remote control capabilities to much more advanced features with a smart remote such as one of the Sensibo devices (sensibo.com), giving you multiple timer options, voice command capability and other features.
– Improving heat pump efficiency
A reverse-cycle air conditioner with high COP and EER ratings will only operate close to these ratings if the installation of the unit is well considered. To maximise efficiency, you want the temperature differential between the indoor and outdoor units to be as small as possible—the system will run more efficiently and use less energy to move a specified amount of heat.
If the unit is primarily used for heating, then it will perform best if the outdoor unit is located in full sun, allowing it to harvest as much warmth as possible. To maintain summer efficiency, which would otherwise be compromised by the sunny location, you can plant a deciduous shrub or tree in front of the unit, or use a simple removable sunshade for the warmer months.
Dust is a great killer of heat pump efficiency—heat does not transfer well through dusty surfaces, so it’s important to reduce dust accumulation in both the indoor and outdoor units. Filters inside the air handling unit should be cleaned regularly, at least once a month if the unit is in regular use. Some systems are now “self cleaning” or have filters that only need to be washed every six months, but they should still be checked regularly. Washable filters can usually just be washed with warm soapy water, rinsed and dried—just follow the manufacturer’s instructions.
The outdoor unit can also suffer from dust buildup on the coils, so check this once a year and use a soft brush to remove any dust buildup. If you have an air compressor, you may be able to blow out the dust just by removing a cover or lid from the unit—but turn the power to the unit off first!
Heat pump hydronic heating
If you are really not a fan of the air movement produced by reverse-cycle air conditioning systems, then you are probably going to go for a hydronic system of some sort.
The heart of a hydronic systems is the water heating unit called the boiler, although the water never boils. The water flows through one or more pipe circuits to one or more radiators, which may be wall-mounted radiators or in-floor pipe coils. These radiatiors emit warmth into the room.
Many boiler systems, particularly heat pump systems, include a storage tank for thermal storage and to provide a buffer, which allows the boiler to run flat out and then turn off for a while, allowing the boiler to operate at maximum efficiency. However, some boilers (usually gas, which we are not covering here) are tankless in that there is no storage tank, although there is usually a small expansion tank to allow for expansion of the water as it heats. They simply heat the water as it circulates through the system.
Hydronic boilers can use a variety of fuel types—natural or LP gas, electrical resistive heating, heat pump and even solar, although the latter are usually boosted with another fuel type due to the variability of solar input. There are solid fuel systems that use wood or wood pellets, but these are far less common.
The cleanest and most efficient boiler type is the heat pump. Like reverse-cycle air conditioners, they heat the water by harvesting and concentrating external heat, so run at greater than 100 % efficiency, and as high as 400 % (a COP of 4) or more.
Most hydronic systems have multiple circuits to allow zoning, where you can heat all or only part of a home. This allows you to leave unused, closed-off rooms and areas unheated to reduce energy use—particularly useful in the shoulder months when heating the entire home is not necessary.
Water is circulated through the system using low-pressure circulation pumps, and circuits are turned on/off by electrically operated valves, usually controlled by an electronic controller. The controller includes timing capabilities to enable a system to heat certain parts of a home at particular times— for example, heating the living areas during the evening and the bedrooms just before bedtime.
Hydronic systems using under-floor coils or skirting radiators (long, narrow radiator panels that replace the regular skirting boards) provide warmth at floor level, so you get the feeling of warmth with lower ambient room temperatures than with space heating. In addition, because there is generally very little air movement with hydronic heating, the potential cooling effect of airflows produced by convective heating such as reverse-cycle air conditioners is virtually eliminated.
Some hydronic systems, particularly those that have been retrofitted to homes and so don’t have in-floor coils, will use radiators that may be mounted near floor level, also providing the advantages mentioned above.
Some radiators are also mounted higher in a room, and some can do double duty (see “Hydronic radiator types” below).
– More than heating?
Some heat pump hydronic systems can also provide cooling in summer, just like reverse- cycle air conditioners. However, not all heat pump systems can do this, so if cooling is required then you will need to specify this to your system designer when getting quotes. This may make for a more expensive system as the heat pump boiler will need to be the reverse-cycle type, but many systems can perform cooling without additional costs, except fans to circulate cooled air in each room. Cooling with hydronics works best with in-floor systems. It can be done with radiator-based systems, but it is unlikely to be as effective as using reverse-cycle AC units.
Some hydronic boilers are also designed to provide domestic hot water, eliminating the need (and cost) for a separate water heater.
– Hydronic radiator types
There is a wide variety of radiator types available for hydronic systems. These include the traditional standing radiators, towel rails, bench seats, skirting boards, mirror surrounds, in-floor trench convectors (radiators embedded in steel boxes fitted into the floor, covered by a grille, used where above-floor radiators are not suitable), ceiling radiators, and even decorative wall art.
Heat pump systems generally run at a lower temperatures (usually 60 °C or so) compared to other heat sources such as gas, which run up to 70 °C or higher. This means radiators may need to be larger for a heat pump system to ensure a similar amount of heat transfer. Your system designer should take this into consideration when designing the system—check to make sure they do.
– What does a system cost?
When it comes to comparing hydronic systems to other forms of heating, up- front costs are a hydronic systems biggest disadvantage. It’s rare for hydronic systems to cost less than five figures, with even a small complete system costing over $10,000. Larger, more complex domestic systems can easily run to $30,000 or more.
Several factors affect the up-front costs, such as the boiler type (the fuel used and whether it is a tank or tankless system), the number of heating circuits, the complexity of the control system and the type and position of the radiators used, which affects the installation labour costs. Retrofitted systems are likely to have higher costs, as pipe runs can be difficult to install due to lack of space inside walls and under floors.
If you are installing a whole-of-house system for a typically sized home, you should not expect costs to be under $20,000, and it can easily be a great deal more, especially if a more advanced heat pump system such as a ground-source heat pump (where heat is extracted from the relatively stable temperature of the earth) is used.
It should also be noted that hydronic heat pump boilers generally have lower COPs than reverse-cycle air conditioners, because the temperature differential between the outside ambient temperature and the target water temperature is usually higher compared to the temperature differential experienced by reverse-cycle units. This is demonstrated in Figure 1, which shows how the efficiency of a heat pump decreases as the differential in temperature increases. This may be partially offset by the improved perceived levels of warmth from hydronic systems over reverse- cycle air conditioners.
– System complexity
Unless the system is an extremely simple one with only one or two manually activated heating circuits, hydronic system plumbing tends to be quite complex. This is a large part of their up-front expense, with labour costs being considerable for larger systems.
The components, including pipes, pumps, valves and tanks, need to be largely hidden from view, and for many homes this may be a problem unless the system was planned for in the house design and a space was set aside for this purpose. For a tidy installation, pipework can be located inside a cupboard or a dedicated “partage” box.
– Thermal lag
An issue that only applies to in-slab hydronic systems is thermal lag. This is the time it takes from when you turn on the heating until you start to feel the warmth underfoot, or from when you turn the system off to when it cools down and stops heating the room. This occurs because of the high thermal mass of a concrete slab, which can take a considerable time to heat up or cool down. If you are away from the house for most of the day and only need heating for an hour or two in the morning and evening, an in-slab system is probably not going to be a good choice. It is not uncommon for occupants with in-slab systems to leave them running all the time due to the lag, and they may even have to resort to opening windows to cool the house off, wasting a considerable amount of heat and increasing running costs.
A system using wall or skirting radiators allows you to turn the heating on and off when desired, and so will provide heat within a minute or so from these types of radiators. Further, in-slab systems need a fully-insulated slab, both underneath and around the edge— otherwise, energy loses to the outside air and soil under the slab can be considerable.
You can have underfloor hydronics even if you don’t have a slab—hydronic coils are combined with heat spreader boards, which have insulation underneath. These can be placed on any sound subfloor (including an existing slab), with your choice of flooring placed over the top. The Tiemme Dry routed floor panel system, which consists of aluminium clad insulating panels with pre-moulded pipe channels, is an example of this sort of product.
– System configurations
Radiators run at higher temperatures than in-slab heating, so a system using these will be configured differently. The temperature difference is substantial: in-floor heating usually uses water temperatures up to 40 °C or so, whereas wall-mounted radiators may run at 60 °C to 70 °C or more. There are also mixed systems, with both water temperatures running in the same system, but not all boilers and system designs can accommodate this. Your hydronic system installer will be able to provide more information on mixed temperature systems.
Because heat pump efficiency drops off at the higher temperatures required for radiators, the most efficient heat pump based system is one that uses in-floor heating and runs at the lower temperatures. That’s not to say heat pumps can’t be used for systems using radiators, but some installers may prefer to do only in-floor heating using heat pumps.
– How about solar?
Depending on the system design and tank configuration, you may be able to add solar thermal boosting using roof-mounted solar collectors that provide proportion of the water heating, while the rest of the heating is done by the heat pump. However, heating is required at times of the year that provide the least solar input, so unless the solar collector array is quite large, the heat pump may do the majority of the work. Generally, a solar hydronic system really can be thought of as a solar-assisted system.
What if you already have a gas hydronic system in place but running costs are too high due to it being an older, inefficient system? In this case, you may be able to have your system’s boiler replaced with a heat pump unit. This will entail selecting a boiler with a heat output similar to what you currently have, which should be listed on the specifications plate of the existing boiler.
Bear in mind, though, that the lower temperatures from a heat pump boiler may mean that existing radiators are undersized and may need to be replaced as well—ask your installer, they should have the experience to be able to assess the suitability of the existing radiators.
Resistive electric heating
Other than with the various heat pump systems already discussed, electric heating is all done using resistive elements, often combined with a fan. Elements are generally made with coils of a special wire that has a higher than usual resistance (all wire has some resistance to electrical flow), although some elements are made of electrically conductive ceramic. Electricity passes through the elements, which heat up due to their resistance to the current flowing through them. The heated elements can emit heat in the form of infrared radiation (the lower the running temperature of the element, the longer the wavelength of the infrared emitted), or a fan can circulate air over the element, expelling the heated air into the room.
– Radiant heaters
Heaters that work by radiating infrared are called radiant heaters, as you might expect. Radiant heaters are designed to heat you (and surfaces in the room) directly, much the way that sunlight feels warm.
A common form of radiant heater is the glowing bar type heater, which uses a resistive wire coil wrapped around or sitting inside a ceramic rod or tube. These types of heaters are ideal for a quick burst of heat for a relatively short duration, although larger units can use a considerable amount of electricity. Unlike a heat pump, radiant heaters are exactly 100% efficient—all the electrical energy they consume is turned into heat.
The main advantages of high-temperature radiant heaters are the low purchase price, the rapid warm-up time and the lack of moving parts and hence high reliability. Radiant heaters can operate for many years with minimal maintenance, although replacement parts, particularly elements, are difficult to come by as these types of heater are so cheap that they are usually replaced when an element fails—although replacing elements rather than the whole device is obviously the preferred option environmentally.
A slightly different form of radiant heat is the far infrared heater. We have looked at these previously, and there are still only a few suppliers, with prices reflecting the lack of competition in this particular market. These heaters also use a resistive element, in the form of a large, flat panel rather than coils of wire. The large surface area compared to the amount of energy flowing through them gives their elements a low energy density and means they operate at much lower temperatures, usually below 120 °C, although some can run at over 200 °C.
The lower operating temperature means they emit longer wavelength infrared radiation than glowing bar heaters and similar high temperature radiant heaters. This long wavelength infrared penetrates clothing quite well, heating you directly, and so they produce a slow, gentle heat that tends to warm you without you realising it until it occurs to you that you are no longer cold. Most far infrared heaters are in the form of a flat panel or elongated strip.
Far infrared heaters are usually mounted on a wall or the ceiling, rather than being portable, so you have to fit one in each room that you want heating in. This can become an expensive proposition compared to the more conventional radiant heaters, although still far cheaper than multiple reverse cycle air conditioners or a full hydronic system.
Another form of resistive radiant heating that runs at an even lower temperature is in-floor heating. This consists of resistive wire or plastic film which has the resistive element printed onto it. It can be laid under carpet or other floor coverings, where hydronic in-floor heating can’t be fitted. It is also far cheaper to install than hydronic heating (and there are even DIY versions available), although in some cases it may need a cement screed over the top before the floor covering is laid down.
However, it is usually much more expensive to run than a heat pump hydronic system due to system efficiency being limited to 100%, like all resistive heating.
– Resistive convection heaters
Another popular type of electric heating is the convection heater, which also uses resistive elements. But instead of emitting heat directly, the elements heat a flow of air drawn through the heater by a fan, making convection heaters another form of space heating. Because they are designed to heat all of a room’s air, which can take quite a while, they take a lot longer to change the thermal comfort of a room than a radiant heater.
The limit for a typical convection heater (or any plug-in domestic electric heater) is 2300 W—the maximum you can draw from a power point. This means that resistive convection heaters will take a lot longer to heat a room than a heat pump, while using a lot more electricity in the process.
Fan heaters are the most common electric convection heater, and they come in many sizes and shapes, with power ratings from 200 W personal heaters to 2300 W room heaters.
Some heaters combine both radiant and convection to give a quick feeling of warmth while slowly heating the room. The now common convective panel heaters come in both free-standing and wall-mounted units, and are usually designed to be subtle and unobtrusive. A popular portable form of combined heater is the ‘oil’ heater, which uses electric elements to heat oil inside the heater, which circulates to distribute the heat to the outer surface of the heater, radiating heat while also heating the air.
A clever take on resistive convection heaters is the heat storage system. These have been available for many years and were found in older homes, especially in Tasmania, but new versions are available from Heatpac (see Figure 2).
These heaters work by using cheap off-peak electricity, such as overnight or in the middle of the day when solar production is at a maximum, to heat a high thermal mass ceramic core. This heat can then be extracted later when needed. For example, you might use electricity billed on a cheap off-peak overnight tariff for heating the home in the morning, recharging the heater during the day from excess solar, ready for the evening peak when you arrive back home from work.
These heaters can store quite a bit of thermal energy, with the largest, the Heatpac Heatwave, storing up to 32 kWh. They can also release heat faster than they store it, so can provide rapid heating when needed. The main disadvantages with these heaters are that they are slow to respond when starting from cold, having to heat the ceramic core to a workable temperature (they are meant to run continuously at working temperature, at least during the colder months), and they are heavy—the Heatpac Heatwave weighs the most at a considerable 215 kg.
– Running costs of resistive heating
Resistive-based electric heating is potentially expensive to run, but estimating the running costs is relatively simple. For heaters that run continuously at a fixed power level, such as radiant heaters, just multiply the power rating (in kW) by the number of hours used and electricity cost per kWh (often called “units” on electricity bills). For example, a 1.5 kW heater run for six hours at $0.30 per kWh will cost 1.5 x 6 x 0.30 = $2.70.
However, most convection and combination type heaters have in-built thermostats that allow them to switch off when the room reaches the desired temperature, causing the power consumption rate to vary during operation. To really know how much energy they are using, you need to use an energy meter to measure them over a given time period.
Bear in mind that many radiant heaters have more than one element, such as the common two- or three-bar heaters. To get their rated output per bar, just divide their maximum rating by the number of bars. For example, a three-bar unit rated at 1800 W would use 600 W per bar, assuming they are all the same size (some heaters have bars of different ratings).
Like all forms of electric heating, resistive heaters can be used to make best use of excess solar PV generation on a sunny winter’s day. If you live in a location that has a good number of such days, then using a heater with a power rating that approximately matches the excess generation can mean you are heating for significantly lower cost. Of course, using that energy in a heat pump system of some sort is much more efficient, providing a lot more heat for the same energy use. As PV systems steadily get larger, many homeowners are finding that they do have an abundance of PV generated electricity at least on some winter days. Even owners of smaller PV systems can gain this advantage if they use personal heating devices rather than space heating or larger radiant heaters.
Solar box heaters
On cold but sunny days, you may be producing good levels of PV electricity, but there is also another source of free energy available—the sunlight itself. Many homes have suitable north-facing windows that can admit considerable solar warmth, but even a home with unsuitable orientation or design can gather solar heat using a rooftop solar air heater: a flat insulated box with a glass top, coated with a solar absorbing surface on the inside. Incoming sunlight heats the air in the box (think of how hot a car gets on a sunny day). The heat can then be transferred by a low-power fan into the home, either directly or via a heat exchanger.
Solar insolation is at its lowest at the time of year that it is needed most for heating— during the winter months—but in places that see a lot of sunny winter days, or places that see relatively sunny shoulder months (late autumn and early spring), where some heating is still needed, solar heating systems can make a real difference to the internal temperature of a home—provided they are sized correctly, of course.
But you don’t have to put a big flat box on the roof to collect solar heat. There is another method that can both warm your home and provide a comfortable indoor space. That, of course, is the sunroom. A properly designed sunroom—one that can be isolated and shaded during summer to prevent heating the home in the hotter months—can provide an enormous benefit on sunny winter days, to the point where no other heating may be needed at all. When designing a home, especially in colder climes, a sunroom— preferably with openable double glazing and adjustable external blinds or shades—should be seriously considered.
What about wood?
That’s a good question, as many people have a preference for burning stuff to produce heat. Aside from the obvious drawbacks of having to lug around small mountains of wood each season (and keep it stored somewhere clean and dry until you need it), there are other serious disadvantages, on which we will touch briefly here.
A lot of firewood is harvested unsustainably from native forests, so that alone should put it off your list of possible options. However, if you have a less environmentally damaging source of wood, then the options are slow combustion heater or masonry heater. We really don’t recommend slow combustion units. While used correctly, they can be reasonably efficient, their design allows for incorrect use way too easily. The two biggest issues are overfilling the firebox, and turning down the air flow to let the fire smoulder. Both behaviours result in the generation of excessive amounts of methane and particulates—not healthy for you or the planet. Indeed, I consider slow combustion heaters to be nothing more than CO2-to- methane machines, with a byproduct of heat.
Masonry heaters are much better—you load up the firebox and the heater does a fast, hot burn, minimising particulates and other pollution. The large amount of heat generated is stored in high thermal mass ceramic plates surrounding the firebox, and the heat radiates into the room in a controlled fashion over the course of many hours. You may only need to do one burn a day, depending on the thermal performance of your home.
Lastly, there’s pellet heaters, which use wood pellets made from sawmill and other woody wastes that would otherwise have gone to landfill. These control the fuel feed rate rather than the airflow rate, and so burn at maximum efficiency all the time, minimising particulates and other pollutants. Their main drawback is the cost of pellets, as there is no bulk pellet delivery option available in Australia (unlike other parts of the world).
Sizing a whole-of-house system
As all hydronic boilers and reverse-cycle air conditioners have a rated heating capacity (and cooling capacity, for reverse-cycle), the first step to sizing a system for your home is to understand the home’s thermal performance—how much heat flows into and out of your home.
Such an assessment is beyond the scope of this article and is really a task for a qualified energy assessor. There are many assessors available and a number of online resources aimed at helping you find one in your area, such as the ABSA website (absa.net.au) or the NatHERS site at nathers.gov.au.
However, if an assessment is not in the budget, then you can make an educated guess with some basic knowledge.
As an example, if you are heating a room and find that a 2000 W fan heater can keep up with heat losses in that room, then you know the maximum heating capacity required will be equal to or less than this. Just run a heater until the room reaches the desired temperature, then start your energy monitor and see how much energy the heater uses maintaining that temperature over the next hour. If, say, the heater uses 1.2 kWh (1200 Wh) to maintain the temperature over the course of an hour (being a fan heater, it has a thermostat and so it won’t draw the full 2000 W continuously), then you know the average power requirement is around 1200 W for that room.
As crude as it sounds, this is actually one of the simplest ways to find out how much heat you need. Set up a fan heater on a cold day and see how it goes. If the room fails to reach the desired temperature after an hour or so, then you have some more insulating and/or sealing to do. If it is nice and toasty warm then simply buy the most efficient system with a rated heat output that you calculated using the above method.
Sizing a hydronic system can be a fairly involved task as it usually means sizing a system for the whole home while matching radiators for each room size. Hydronic system sizing is probably best left to the system designer/installer. However, bear in mind that many installers assume a particular level of thermal performance based on their experience with Australian homes. That average performance will be pretty poor, so if your home has been well sealed and insulated, the installer may over-specify the heating capacity, so make sure they understand your home’s thermal performance.
The most suitable heating
You want your house to have the best thermal performance possible—with minimised heat loss through the building envelope and draughts. Without retrofits, many homes will only perform averagely at best, so it makes sense to seal as many gaps as possible, and install insulation where you are able. At the very least you should have roof cavity insulation, but consider wall, underfloor and window insulation as well.
If you are happy that your house performs as well thermally as you can easily make it, you then need to determine which form of heating is the most suitable for you: convective (space) heating, radiant heating, or a combination?
That really depends on the preferences of the occupants—some like the air to be warm, while others will prefer direct radiant heat.
Also, some people are happy heating just the room they are in, while others, who may move from room to room regularly, may want to heat the whole house, or a much larger portion of it. If you are happy heating single rooms as you use them, then a small radiant heater, far infrared heater or a high efficiency small split system air conditioner in each room to be heated might be the best option. For room-to-room heating, you need heaters that make you feel warm quickly, so systems with large thermal lag, such as in-floor hydronics, are not suitable.
For draughty homes, where the level of air changes per hour is relatively high, you don’t want to be using space heaters, as you lose that heated air quite rapidly. In this case, radiant heaters will be the best option, with far infrared probably the best due to their high level of effective warmth from relatively low power levels.
For well-sealed, well-insulated homes with good thermal performance, space heating will usually be the preferred option, with reverse-cycle air conditioning being the best performing option on energy use, and heat pump hydronic being a fairly close second.
For a small, very well-insulated high performance open-plan home, a simple fan heater may be all that’s required. While they use a lot more energy for the heat provided, when the heat stays in the home and minimal heat input is required anyway, more expensive options like air conditioners and hydronic systems may never pay for themselves in energy savings, especially if the home has a well-sized solar system. In this situation, simpler is best.
In bathrooms, where heating is usually needed only for short periods, radiant heating is usually the simplest and most effective solution, unless the house has a whole-of-house ducted or hydronic system.
Combination radiant heater/light/fan units have been the standard solution for bathrooms for decades, because they are simple and effective, but they do have several disadvantages. These include the common occurrence of the radiant bulbs being used as extra lighting (often being left on in the process), and the poor or non-existant draught sealing of such units, allowing considerable airflows between the room and the roof cavity. Some units do have in-built draught excluders (such as the IXL Tastic Eco Sensation) but the quality and effectiveness of these varies.
If a bathroom has a separate light and fan, then a simple wall-mounted strip radiant heater can provide fast warmth when needed, with minimal purchase and installation cost.
Heated towel rails are a common bathroom fitting, and may be part of the hydronic system or separate resistive electric units.
However, the latter should be placed on a timer as they are easy to accidentally leave on 24/7. A 100 W towel rail will consume 2.4 kWh per day if left on—that’s over $200 of electricity per year if it is never turned off!
Energy rating labels
Most people are now familiar with standard appliance energy rating labels. However, as the climate zone in which a reverse-cycle unit is installed can affect its performance, they have their own special labels—the Zoned Energy Rating Label, which covers performance in different climates.
These zones, which span both Australia and New Zealand, are labelled Hot, Average and Cold. The label—a sample of which is provided here—sets out the heating (and cooling) capacity of the appliance at specific outdoor temperatures in each of three
separate zones, as well as a star rating and energy consumption information for each zone. There’s even maximum noise levels for inside and outside, making it much easier to compare performance across different air conditioner models without having to refer to datasheets or websites.
The cheapest heating
Determining which is the cheapest heating for your needs requires considering both the upfront cost and running costs of potential options. This particularly applies when heating needs are low. Spending $2000 on a reverse-cycle air conditioner is not a good investment when a $100 fan heater will do the job—provided that heating needs are low enough that the extra energy cost of the fan heater is less than 10% of the difference in price of the two systems. Of course, you may prefer to prioritise energy use reduction to reduce your environmental footprint, but also bear in mind that the emissions created making something as complex as a reverse cycle air conditioner is vastly greater than those to make a simple fan heater. Of course, it’s impossible to quantify those emissions, but if you buy accredited GreenPower, the bulk of the life cycle emissions will indeed be from manufacturing the system, not running it, so consider your priorities.
For whole-of-house heating systems, weigh up possible options that may not be immediately obvious, but which may swing the decision toward one particular system. As an example, you could spend $20,000 on a hydronic system, but a more versatile alternative would be spend that same amount of money on several reverse-cycle split system units, plus a 10 kW solar PV system.
The PV system will help offset some of the heating costs in winter, while generating a huge amount of energy over the rest of the year, producing a considerable amount of energy credit towards heating for the next winter. The PV plus reverse-cycle option may be effectively “free” (or even cost negative) to run, while the the hydronics won’t be unless you spend extra on the PV system.
It may sound like hydronics doesn’t compare so well financially with reverse cycle air conditioning, and in reality that is usually true. Complexity means higher cost, and there’s no avoiding the fact that hydronic systems are complex—with pumps, valves, many metres of piping, and often a great deal of work required to install them. The one thing that often sways homeowners towards hydronics is the feeling of warmth underfoot, but it can be an expensive feeling to have installed and it really is not the best option if you are budget conscious.
However, one more appealing aspect hydronics’ have is that hydronic systems tend to feel more comfortable at lower temperatures than reverse-cycle air conditioners as the heat is at floor level, and there is no cooling effect from air movement. With heat pump hydronics, you might also be able to access a cheaper off-peak tariff to heat the water, at least for part of the day. This will depend on your system’s design and your energy company’s tariffs, but it’s something to look into when weighing up whole-of-house heating options.
Reducing energy use even further
You might think that an ultra-efficient heat pump is the lowest energy using heating you can run, but that’s not entirely accurate.
There is a way to go even lower in energy use and running costs—the often overlooked personal heating, which involves heating only the house occupants, not the house itself.
Radiant heaters are a step towards this, but they still heat all objects in front of them. The ultimate low-cost heating is purely personal heating, where the occupants use devices to keep only themselves warm.
Personal heating can use active methods, such as tiny personal heaters designed for one person, and heated clothing, throws and blankets (my heavily used Sunbeam EP5000 heat pad is still going strong after quite a few years—they are well worth the investment). There is also the old favourite, the hot water bottle, but we highly discourage the use of these as they can burst and scald you, or at least make a mess. An alternative is the Snugglesafe disk pictured on page 69. It’s designed for pets but works for humans too.
Alternatively, you can opt for simple passive methods of staying warm, which simply means wearing enough clothes and other textiles to keep you warm. With so many amazingly warm textiles readily available, it is perfectly viable to keep yourself nice and comfortable using nothing but your own body heat.
If you go down this route, just remember, pets get cold too, so your dog or cat will need their own form of personal heating, whether it be an insulated bed (cat caves work well for cats or dogs) or a heated pet mat (make sure you buy a good quality unit with thermal control). One of my favourites is the Snugglesafe disk, as mentioned above. You throw it in the microwave for a few minutes and the phase-change material inside emits heat at a fixed temperature for many hours. They never wear out, they can’t burst or cause a fire, and they are extremely easy to clean.
Being a renter has its advantages, but staying comfortable can be more difficult as, being unable to make permanent changes to the home, renters are limited in their heating options. Rental homes often perform poorly thermally compared to owner-occupied homes, and while some landlords are open to improvements, many are not. So how can renters stay warm without spending a fortune on energy bills?
Many of the options discussed here so far also apply to rental homes. Renters need to focus more on heating themselves, and personal heating is generally the cheapest and simplest option. Small personal heaters can also work, as can low power far infrared heaters. Many smaller panel heaters come with castors so they can be used as portable heaters, but make sure you know the power consumption of your heater.
If you spend a lot of time in one room, you may choose to simply heat that room and leave the rest of the home unheated. In this case, insulate the room as well as possible, with thick rugs on the floor (or cork flooring mats for a healthier option) and full-length wall drapes, rugs or other insulative materials covering as much of the walls as possible to help retain heat. Adding window insulation such as bubble-glazing (bubblewrap taped to the glass) or any other insulating material to windows will also help cut down heat loss. Finish off with draught excluders on doors.
It’s rare that a landlord will allow renters to install split system air conditioners, but they can still use portable reverse-cycle air conditioners as they need no permanent installation. These generally have lower COPs than a fixed split system, but can still reach COPs of up to 3 if used correctly. The only requirement for installation is an openable sliding window such as a sash windows to install the outlet duct and water drain hose, which passes through the window opening via an adjustable plate or seal system designed to let these pipes exit a window with minimal air leakage. Once fitted and with the window closed as far as possible, judicious use of foam rubber (an old foam cushion or pillow will have plenty of material, but closed cell foam is best to reduce air leakage) allows you to seal the window pretty much completely. Some units even come with flexible seal systems that allow you to use the units with other window types, such as hinged windows.
Portable air conditioners usually have only one outlet duct—the air exhausted from this duct actually comes from the room. This also reduces their possible efficiency as they draw air into the home from outside. There are some (rather rare) portable units that have two ducts, to allow air from outside to both enter and exit the unit for heat transfer, so cold outdoor air never enters the room. These work much like a split system, except that both halves of the unit are indoors, and they tend to have the highest COPs of all portable units.
Be aware that some “reverse-cycle” portable air conditioners are in fact not reverse cycle units at all. They have a heat pump cooling system, but simple resistive elements for heating. Just check the specifications—if the power consumption rating is the same as the heating output when in heating mode, they are using resistive heaters. True reverse-cycle units are readily available and cheap: units with outputs up to 4.7 kW of heating can be had for under $600. Of course, reliability can be hard to determine, so do your research and look at reviews, especially from those who have had the units for some time; Choice has reviewed these types of unit. Also check noise level ratings, as portable air conditioners can be quite noisy.
Another option may be a box air conditioner. Like portables, these are self- contained units that are designed to sit in an open window or hole in the wall. You will need to fasten them securely in place, including the external support frame, but as this only requires a few small screw holes, landlords may be much more willing to give permission.
Are there any regulations aimed at improving heating standards for renters? Well, not a lot, but Victoria, at least, has minimum heating standards for rental homes (see bit.ly/ VMHPSR). These require that:
- A fixed heater in good working order must be present in the main living area of the rented premises; or
- If a fixed heater has not been previously installed in the rented premises’ main living In that case, an energy efficient fixed heater, which is in good working order, must be installed in the leased premises’ main living area.
Because of their very nature, heaters can pose much more of a hazard than other appliances if not used with care, and there are certain rules to follow when using certain types of heaters, especially high-temperature heaters.
It should go without saying, but keep heaters well clear of combustible materials in the home to eliminate the chances of the heater setting anything alight. This particularly applies to use near furniture— your dog can easily knock a cushion off the couch onto a heater (I’ve seen it happen), and curtains can be drawn into the air inflow duct of convection heaters.
Never leave a high-temperature radiant heater running unattended, and never underestimate the possibility of fire risk from this type of heater. Also avoid the use of high- temperature heaters around children or pets, as they can easily cause burns in an instant to the unwary. Use low-temperature heaters (with outlet air temperatures or surface temperatures below 50 °C if possible) or wall- mounted heaters out of harm’s reach.
While many people do it, you should never cover any heater with clothing or towels, even low-temperature panel heaters and oil-filled heaters, as they may overheat and damage the heater itself (depending on how well the heater is designed), even if no fire occurs. The only exception is those heaters designed for the task, such as heated towel rails, or heaters that have a fixed temperature heat source, such as hydronic radiators.
You should also consider electrical safety when using plug-in heaters. The high current draw of many heater types can produce heating of plugs and power points if they are not in good condition. The contacts in the power point and plug pins are metal which will eventually tarnish (oxidise) over time, This reduces the electrical contact area and acts like a low value resistor, causing heating of the plug and power point contacts.
If you notice heating of the plug or cable of the heater after it’s been running a while, then you may need to replace the plug or the power point.
It’s also highly recommended to plug heaters directly into power points—do not use extension cords or power strips as they are often quite light duty devices and can heat up. If you must use an extension cord, the $5 cheapie from the local hardware store is not the cord to use—buy a heavy duty cord of suitable length, and do not operate the heater with either the extension cord or the heater’s cord partially coiled. Really, heater safety is just common sense—assume the worst possible scenario is just waiting to happen, and make sure you avoid it!
|System type||Cost range||Running costs||Pros||Cons|
|Split system reverse- cycle air conditioner||$1 k to $5 k or more per unit||Low to medium||Fast, effective heating. Low running costs if home is thermally efficient||Outdoor units can be unattractive and noisy. Moving air may reduce thermal comfort|
|Ducted reverse-cycle air conditioner||Up to $20 k or more||Medium||Can heat a whole home quickly||Zoning can be limited, resulting in excess energy use. Ducts prone to vermin damage, damaged ducts can greatly increase running costs without being obvious. Less efficient than individual splits|
|In-slab hydronic||$10 k up to $30 k or more, depending on options||Low to high, depending on heat source/boiler type||Produces warmth underfoot, very effective heating||Zoning can be limited, resulting in excess energy use. Ducts prone to vermin damage, damaged ducts can greatly increase running costs without being obvious. Less efficient than individual splits|
|Radiator hydronic||$10 k up to $30 k or more, depending on options||Low to high, depending on heat source/boiler type||Produces radiant warmth near floor level, very effective heating. Warms up much faster than in-slab hydronics||Plumbing can be complex, many possible points of failure (pumps, valves, pipe joins)|
|In-floor resistive electric||Up to a few $k per room||High||Easy retrofit to most rooms, provides underfoot heat like hydronics but without the thermal lag||Can be very expensive to run if used for many hours per day, especially if the house performs poorly thermally|
|Radiant electric||$15 to $500||Medium to high, depending how used||Instant heat, direct heating of occupants||High running cost if used for many hours per day, replacement elements usually not available, fire risk if misused. May not cover heating needs of large room|
|Convection electric||$15 to $400||Medium to high, depending how used||Zero maintenance, long lifespan||Effective heat-up time can be long as heats air rather than occupants. High running cost if used for many hours per day, especially if the house performs poorly thermally. May not cover heating needs of large room|
|Combination electric||$50 to $1000||Medium to high, depending how used||Relatively fast thermal comfort||High running cost if used for many hours per day, especially if the house performs poorly thermally. May not cover heating needs of large room|
|Far infrared radiant||$100 to $1000 per room||Medium to high, depending how used||Relatively fast thermal comfort, heats occupants rather than air in room.|
Produces a ‘zone of warmth’ effect. Zero maintenance, long lifespan
|High running cost if used for many hours per day|
|Storage convection||$1000 to $4000 plus installation, depending on options||Low to high, depending on tariffs and available solar||Fast thermal comfort, long lifespan, quiet, allows best use of excess solar generation or off-peak tariffs, can output more power than rated electrical connection||Units are heavy, particularly the higher storage models, expensive to run if off-peak or solar not available|
|Solar thermal (solar box heaters)||$500 to $5000 or more||Zero to very low||Virtually free heat, low maintenance||May look unattractive, heat often not available when needed most, requires good solar access|
|Solid fuel||$500 to $5000 or more||Low to high, depending on fuel source||Cheap to run in some cases, if local fuel is available or a waste product is used as fuel. High radiant warmth||High particulate emissions in many cases (unhealthy), potentially high methane emissions, many fuel sources destroy forests. Regular cleaning and maintenance required|
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