A breath of fresh air

Monitoring air quality could transform how you live in your home. Rachel Rose explains why and how.

Humans are very good at sensing temperature: we have built-in monitors for too hot, too cold and the comfy spot in between. True, it varies between individuals and is relative in other ways, but generally we get it. When it comes to sensing the quality of the air we breathe, though? We can’t see it and we don’t really feel it. By the time our senses can detect the air is polluted, indoor air quality (IAQ) is usually seriously bad. And carbon monoxide and some fine particulate matter can’t be picked up at all.

“People tolerate stuffy rooms or symptoms such as headaches, eye and nose symptoms and asthma without recognising that these may be a sign of poor air quality,” writes Julie Bennett, a public health researcher from the University of Otago, in a recent paper. “The challenge is that air remains invisible, undervalued and largely absent from building codes and health policy.”

Indoor air quality is impacted in a number of ways. Fine particulate matter builds up from burning things: the use of gas for heating or cooking, wood fires, even burning the toast. Fabrics, furnishings and floor covering may offgas volatile organic compounds (VOCs). We create moisture in our homes just by breathing, cooking and showering; too little ventilation sees humidity levels climb, particularly when a house is underheated. And a damp house is more vulnerable to developing mould, which can aggravate conditions like asthma and respiratory disease or trigger allergic reactions.

Carbon dioxide (CO₂) levels quickly elevate when people are inside buildings without sufficient ventilation. CO₂ over 1,000 parts per million (ppm) makes people progressively less able to think clearly or concentrate, and is linked to tiredness, headaches, dizziness, increased blood pressure and heart rate, and poor quality sleep.

A reliable monitor showing indoor temperature, relative humidity (RH) and CO₂ levels can tell us a lot about the health of our home and dramatically improve IAQ by training us to ventilate sufficiently.

Australians and New Zealanders are big on natural ventilation. Our building codes require operable windows of a minimum area, and even in wet areas like bathrooms, the first line assumption is that an open window is sufficient to ventilate the space. But these assumptions are usually wrong. Opening just a single window is often insufficient, and even cross ventilation doesn’t work in still conditions.

My partner and I and a big dog lived in a small caravan on our house site near Whanganui here in New Zealand for several years. I bought an Aranet CO₂ monitor that also reports temperature and RH, and the data changed our habits of a lifetime after we woke one morning to CO₂ levels over 3,000ppm. Over a couple of weeks, the numbers on the monitor trained me to identify the physical experience of breathing in fuggy CO₂ -saturated air.

It pushed us to start actively ventilating, even when it was very cold outside and the heater was running. We discovered the ‘trickle vent’ setting on the caravan windows alone was completely ineffective. We upgraded the tiny fan in the kitchen area and left it running continuously whenever the caravan was occupied. The tendrils of cold draught weren’t pleasant, but it was a price we were willing to pay once we could see the impact of our choices on the monitor’s CO₂ readout. It was also feasible, as we needed so little active heating to keep the small, well-insulated space comfortable anyway.

However, relative humidity remained stubbornly high, around 65 to 75 per cent, despite us taking every precaution. We didn’t use the gas cooking facilities (we built an electric camp kitchen in the shed next to the caravan), and wet clothes and towels were banished outside.

We still check the monitor regularly now that we’ve completed and are living in our new Passive House (see Sanctuary 71 for more on the house). With our efficient mechanical ventilation system running all the time, it’s really easy to keep in the ‘Goldilocks zone’ across all three metrics. The natural materials used in our house buffer humidity and help regulate temperature. We confidently run our mechanical ventilation unit at a lower setting than expected, thanks to the monitoring data. It was also very helpful during a power cut that shut the ventilation system down for hours on a winter evening, letting us know when it was time to open some windows and trade off the cold for lower CO₂ levels.

I highly recommend air quality monitoring for any home that relies on opening windows for ventilation. While this approach can provide adequate ventilation in theory, it does rely on humans being home to open and close windows, and being willing to do so even when maintaining acceptable CO₂ and RH levels involves a cost to thermal comfort or peace and quiet.

It’s worth noting that some experts think detection of particulate matter, especially the fine PM2.5, is even more important than CO₂ . We’ll cover PM2.5 and VOCs, along with various strategies for improving ventilation, in future articles.