Open windows even in winter?

The facts

No doubt, if it really needs to be mentioned, opening windows (or mechanical ventilation) can make a difference to indoor air quality. Work published in the early 2000s observed that even a single window could be opened Double or triple the speed of change Air in a house. And many other studies have shown this Clearly improved Some air quality indicators, such as CO2 concentration (When we breathe in we breathe out). There are some Found the link with Sleep quality.

Now, do you have to do this every day, even in winter? Generally speaking and a bit theoretically, the answer is yes. But in practice, there’s a whole range of nuances and conditions that mean it’s not equally beneficial for everyone, or in all households.

“In the 2000s, in the scientific literature, we tried to figure out what level of ventilation is beneficial, and we started to see benefits with 0.5 air changes per hour. In Canada, because of the cold in the winter, we have a standard of 0.3 per hour instead, which forces us to make compromises,” says the National Institute of Public Health. (INSPQ) consultant Patrick Poulin explained.

In some old, poorly insulated houses, we can easily reach this threshold without a ventilation system or opening windows, he continues. In the 1950s and 1960s, “a lot less airtight buildings were built than now, no vapor barrier, windows less airtight, etc. So with passive natural ventilation alone, without opening the window, we achieved six air changes per hour in extreme cases. (…) It was a time when energy was much cheaper than now, so houses were built [sans trop se soucier de leur efficacité énergétique]”.

So there are dwellings where ventilation efforts are ineffective – but this is clearly only the case for a minority of households. In most cases, opening windows or using a mechanical ventilation system is recommended. A review of the scientific literature Published in 2021 in Indoor air The average air change rate for 40,000 dwellings is 0.5/h, but in some studies it is as low as 0.2/h.

Even without symptoms

INSPQ listed a A series of features (eye or throat irritation, recurrent sinusitis, headaches, concentration problems, etc.) This indicates the presence of an air quality problem in a home, especially if they are felt in certain areas. Certain moments (after moving or rebuilding, after a flood, etc.) and many residents at the same time. But even if there are no symptoms, it’s important to regularly ventilate your home, suggests INSPQ public health consultant Dr Stéphane Perron.

“The greatest enemy of buildings is moisture, and humans produce a lot of it through breathing,” he says. If we go over a certain limit, around 60%, the air will grow insects and molds and that will degrade the air quality for everyone. And that’s without counting other pollutants that accumulate in the home, such as “volatile organic compounds” (paints, varnishes, cleaning products, etc.).

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

That being said, there is also the question of context to take into account, he adds. Temperature-related discomfort during extreme cold is not worth it. For example, in a home near a highway, it’s not a good idea to open your windows during rush hour, when the air outside is likely to be worse than inside. An allergy sufferer would be wise to keep everything covered during pollen season. And so on.

Better than open windows

Finally, Mr. Since Blanchette’s question refers to “ventilation systems”, opening windows in houses equipped with them becomes redundant, unnecessary. We have to be clear about what we mean by a “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. Poulin said, mechanical ventilation (though expensive) is often more effective than open windows. “We can’t have precise control of ventilation when we open the windows,” he says. At certain times, like in winter, it is very effective because there is a big difference in temperature with the outside, but the cold causes discomfort and the air exchanges do not necessarily happen where we need them. So it’s a bit random and it makes the health benefit a bit theoretical.

On this topic, therefore, the text of Protect yourself False: A good ventilation system usually eliminates the need to open windows in winter.

judgment

All very true. Indoor air quality deteriorates without air exchange, and opening windows has been well proven to accelerate indoor air renewal. But it’s not an absolute rule — for people with allergies, for example, it’s best to keep everything closed during pollen season — and “the idea that a home’s ‘ventilation system’ should be open is wrong. .