The ideal relative humidity level in a Quebec home is between 30 and 50 percent, a range agreed upon by the INSPQ and federal authorities. In winter, the target drops to around 30%, and even 25% in freezing weather, because condensation forms on cold surfaces long before the air becomes uncomfortable.
A single range covers most of the year. According to the INSPQ, several organizations place the optimal value between 30 and 50 percent, and this balance must be maintained over the long term to ensure both the comfort of the occupants and the integrity of the building’s components (INSPQ).
This percentage represents the amount of water vapor in the air relative to the maximum amount that air can hold at room temperature. It is this relationship with temperature that explains why the same amount of water vapor is tolerable in July but becomes a problem in January. The setpoint is therefore not a single number engraved on the thermostat, but a value that changes with the calendar.
Québec puts the same idea another way: the air must remain dry enough to prevent fogging, usually between 30 and 55% (Québec.ca). The two ranges overlap, and the practical advice can be summed up in a single line: aim for the lower end when it’s freezing, and the upper end when it’s mild.
Relative humidity targets by season, according to the INSPQ, Quebec.ca, and the federal guidance document.
The extreme cold calls for the lowest setting of the year. The INSPQ reports that at temperatures below -10 °C, the Canada Mortgage and Housing Corporation recommends 30%, or even 25% in very cold conditions, specifically to prevent condensation on windows and walls (INSPQ, relative humidity measurements).
The federal agency reaches the same conclusion in its guidance document for professionals: maintain a low level— below 50% in the summer and around 30% in cooler weather—in accordance with the building envelope’s maximum allowable values (federal guidance document).
This point about the window frame deserves attention. A house built in 1965 with single-pane windows will show condensation at 30%, whereas a well-insulated, recently built home will withstand that level. The right setting for a harsh winter isn’t the same as your neighbor’s: it’s the highest setting at which your own windows remain dry on a freezing morning.
From June to September, the problem is reversed. The outside air is humid, the basement is cool, and moisture condenses on the foundation walls and ducts. The government therefore recommends using a dehumidifier when outdoor humidity exceeds 70% in the summer, and emphasizes that opening windows at that time would only make the situation in the basement worse (Québec.ca).
In the spring and fall, the house practically regulates itself. These are the two times of year when maintaining a humidity level of 40 to 50 percent requires little effort, since the difference between indoor and outdoor humidity remains small. This is also the best time to perform maintenance, which is most effective during the colder months.
A hygrometer costing less than twenty dollars is all you need to tell if the air is too humid.
Condensation isn’t a window defect—it’s an indicator. Québec is clear on this: its regular presence on windows and walls signals that a room is too stuffy. A light film that disappears an hour after sunrise is still normal in January. Drops running down the window frame, dark rings on the wood, or ice at the bottom of the windowpane call for corrective action.
The reverse is also true. If the reading shows 45% and nothing is beading at -20 °C, there’s no reason to lower it to 30% just to meet a target. The cold surfaces are the deciding factor, not the setpoint.
Persistent excess humidity does more than just fog up the windows. The INSPQ points out that it can condense inside walls, damage the structure, and increase emissions of volatile organic compounds—formaldehyde in particular—released by finishing materials.
Below 30%, discomfort has been documented: dry skin, eyes, nasal passages, and throat. The INSPQ adds that very dry air promotes the survival of several viruses, including rhinoviruses, influenza, and human rotaviruses. The temptation, then, is to increase the humidity, which directly leads back to the problem of fogging.
When humidity exceeds 60% over an extended period, dust mites, fungi, and certain bacteria thrive. The organization sets the theoretical maximum at 65%, with the threshold—which should not be exceeded—ranging from 60% to 70% depending on the sources consulted.
Within these limits, there is real flexibility. A household dealing with asthma is better off staying in the lower half: it is dust mites and mold—not dryness—that trigger symptoms.
No setting will hold without taking readings. Québec notes that hygrometers are sold at low cost in most hardware stores. A single instrument is enough to get started; two or three provide a much more accurate reading of a multi-story house.
When readings remain high for no apparent reason, or when a musty odor persists, a bacteriological air test can reveal what is actually present in the air before any work is undertaken.
A clogged filter causes the readings to spike, and no one understands why.
It all starts with the sources. Quebec recommends limiting frequent long showers, running fans while bathing and cooking, making sure the dryer vent leads outside, using humidifiers sparingly, emptying and cleaning the dehumidifier’s water tank, and to avoid storing firewood indoors.
Next comes mechanical ventilation. In an airtight home, a heat recovery ventilator (HRV) removes stale air and replaces it with fresh air. But it has to be working properly: clogged filters, a blocked heat exchanger, or intermittent operation cause energy bills to rise without anyone understanding why. Cleaning the heat exchanger often restores the lost airflow, and cleaning the ducts resolves issues throughout the rest of the system when dust builds up too quickly.
For supplemental ventilation in January, the official recommendation is brief: open two windows for two to three minutes, depending on the outside temperature. That’s enough to refresh the air, but not enough to cool the building materials.
A reading that refuses to go down despite good ventilation almost always indicates a water leak. The INSPQ lists the main sources: rainwater infiltration due to faulty drainage or cracked foundations, sewer backup, plumbing leaks, condensation on a thermal bridge, and moisture produced by the occupants.
The response time is the key factor to remember. Quebec requires that all water damage be completely dried out within 24 to 48 hours, and that severely damaged porous materials—such as drywall, carpets, insulation, and upholstered furniture—be discarded.
When it comes to stains, the same source distinguishes between different cases. A windowsill can be cleaned with a clean cloth and an all-purpose cleaner that does not contain bleach. However, if the affected surfaces exceed 1 m², are numerous, difficult to clean, or reappear after cleaning, you should hire a specialized company. This is the threshold at which preventing and treating fungal contamination with the help of experts becomes the right decision rather than just a knee-jerk reaction.
Controlling humidity levels comes down to a few simple, repeated steps—never to a one-time purchase. Our advice fits into a short checklist: check the hygrometer once a week, clean the central system’s filters when temperatures change, adjust the humidifier’s settings as soon as condensation appears, and have the system inspected by specialists every two or three years. A well-ventilated home in Quebec is characterized by subtle signs: a constant supply of fresh air, dry windows even when temperatures drop below -20 °C, and no suspicious odors in the basement.
One final point to consider: the target is not the same for everyone. Indoor air quality specialists adjust their approach based on the age of the building, the number of occupants, and the season. In a Quebec home heated by a central system, the heat already dries out the air, and humidification becomes unnecessary below certain outdoor temperatures. Sustainable solutions start with a well-ventilated environment and regular maintenance, not just another gadget. This is the only path to healthy air, and our advice always comes back to this fundamental principle.
A humidity level that refuses to drop in winter, fogged-up windows, or a musty odor often point to a clogged air exchanger or dust-clogged ducts. Ventilo Exp’air cleans and inspects ventilation systems in Granby and the Estrie region in accordance with NADCA and ANCV2020 standards, including robotic inspection and air quality analysis as needed.
Contact us for a customized assessment.
Around 30%. Below -10 °C, CMHC recommends lowering it to 30% and down to 25% in very cold conditions to prevent condensation on windows and walls. If your windows stay dry at higher humidity levels, your home’s envelope can handle it.
Yes, if it lasts that long. According to the INSPQ, if humidity remains above 60% for an extended period, conditions become favorable for dust mites, fungi, and certain bacteria; the INSPQ sets the upper limit at 65%.
Because the air contains more moisture than cold surfaces can handle. Reduce the humidification, turn on the bathroom and kitchen fans, and then check that the air exchanger is working properly.
The dehumidifier addresses localized excess moisture, especially in the basement during the summer. The HRV circulates fresh air throughout the entire house and remains the best option during the colder months, since outdoor air is naturally dry once it is heated.
A quick daily check is sufficient during periods of extreme cold and heat waves. The rest of the year, a weekly glance is enough to spot any drift before it leaves marks on the frames.
