Open windows even in winter?

facts

There’s no doubt, if anything, that opening windows (or mechanical ventilation) makes a difference in indoor air quality. Work published in the early 2000s noted that opening a single window could do this Double or triple the pace of change The air in the house. Many other studies have shown that this Clearly improved Some air quality indicators, Such as carbon dioxide concentration (which we exhale when breathing). Some even have Found the link with Sleep quality.

Now, does this mean you have to do this every day, even in the winter? Generally and somewhat theoretically, the answer is somewhat yes. But there are, in practice, a whole series of nuances and conditions that mean they are not equally useful for everyone, nor in all homes.

“In the 2000s, we tried in the scientific literature to define what level of ventilation was useful, and we started to see benefits at around 0.5 air changes per hour. “In Canada, we kept the standard of 0.3 per hour because of the winter cold, which forces us to make compromises,” explains Patrick. Pauline, consultant at the National Institute of Public Health (INSPQ).

He continued: “It can happen, in some old, poorly insulated homes, that we easily reach this threshold without having a ventilation system or opening windows.” In the 1950s and 1960s, “buildings were built that were less airtight than they are now, there was no vapor barrier, the windows were less airtight, etc. Through passive natural ventilation, we were able to achieve up to six air changes per hour in extreme cases, even without opening a window. (…) Energy was much cheaper than now, so houses were built [sans trop se soucier de leur efficacité énergétique]”.

So there are dwellings where there is no point in exerting ventilation efforts – but this is clearly only relevant to a minority of homes. In most cases, it is recommended to open windows or use a mechanical ventilation system. Review of scientific literature Published in 2021 in Indoor air The rate of air change in 40,000 dwellings was found to average 0.5/hour, but was as low as 0.2/hour in some studies.

Even without symptoms

INSPQ has listed a A series of symptoms (irritation of the eyes or throat, recurrent sinusitis, headaches, concentration problems, etc.) which can indicate an air quality problem in the home, especially if it is felt in certain areas for certain moments (after a move or renovations, after a flood, etc.) and by several passengers at the same time. But even if there are no symptoms, it is still important to ventilate your home regularly, notes Dr. Stephane Peron, public health advisor at INSPQ.

“The biggest enemy of buildings is moisture, and humans produce a lot of it through breathing,” he says. If we go beyond a certain limit, about 60%, we will see an increase in mites and mold in the air, which will lead to lower air quality for everyone. This is without taking into account other pollutants that can accumulate in the home, such as “volatile organic compounds” (from paints, varnishes, cleaning products, etc.).

“The only way to get rid of it is to ventilate it,” says Dr. Perron.

He adds that there is also the issue of context to consider. Temperature-related discomfort may not be worth it during extreme cold. In a home located near a freeway, for example, it’s probably not wise to open the windows during rush hour, when the air outside is worse than the air inside. An allergic person would be wise to keep everything closed during pollen season. And so on.

Better than open windows

Finally, since Mr. Blanchett’s question mentions “ventilation systems,” let us add that opening windows becomes redundant, and unnecessary, in homes equipped with them. Obviously we need to agree on what we mean by “ventilation system” — simple ceiling fans probably aren’t enough — but homes with mechanical air exchange systems don’t need to open their windows.

In fact, Mr. Bolin says, mechanical ventilation (even if expensive) is often more effective than open windows. “We can’t precisely control ventilation when we open the windows,” he says. At certain times like winter, it can be very effective because there is a large temperature difference with the outside, but the cold causes discomfort and air exchange does not necessarily occur where we need it most. So it’s a bit random and that makes the health benefits a bit theoretical.

In this sense the text came Protect yourselves It was wrong: a good ventilation system generally eliminates the need to open windows in winter.

Judgment

Very true in general. Indoor air quality will deteriorate without air exchange, and it is well proven that opening windows speeds up the air renewal process in a home. But this is not an absolute rule – for someone with allergies, for example, it is better to keep everything closed during pollen season – and the idea that one should open up even if the house is equipped with a “ventilation system” is wrong.