Indoor Humidity in Toronto — Why It's a Cleaning and Maintenance Issue
Toronto's climate generates two distinct indoor humidity challenges over the course of the year: excessive humidity in summer (Toronto's humid continental climate means July–August days with 80–90% outdoor relative humidity, which translates directly into indoor humidity problems in homes and condos without adequate dehumidification), and excessive dryness in winter (forced-air heating without humidification drops indoor RH to 20–25% in deep winter). The summer humidity problem is the more significant cleaning and maintenance concern for most Toronto homeowners — indoor RH above 60% creates conditions for mould growth, dust mite proliferation, musty odours, and the condensation on cold surfaces (water pipes, concrete basement floors, air-conditioned spaces) that leads to surface damage. Managing indoor humidity to the optimal 40–50% RH range year-round is a meaningful home maintenance practice.
Identifying High Humidity in Your Toronto Home
- Condensation on windows: Visible condensation on the inner surface of windows during summer indicates indoor humidity is above 60% — the glass surface is cool enough (from air conditioning) to condense the humid indoor air
- Musty smell: A persistent musty odour in basements or certain rooms indicates mould growth, which requires sustained high humidity (above 60% RH) to establish
- Visible mould: In bathrooms, windowsills, and basement corners — the most direct indicator
- Sticky or heavy-feeling air: Simply the physical sensation of high humidity in poorly ventilated spaces
- Hygrometer reading: An inexpensive digital hygrometer (Inkbird, Govee — available at Canadian Tire in Toronto for $15–30) gives you an actual RH reading — the clearest way to know
Strategies to Reduce Humidity in Toronto Homes
Dehumidifier (Most Effective)
A basement dehumidifier running during humid months (June–September) is the single most effective humidity control intervention for Toronto homes with basements. Toronto basements — below grade, with concrete walls that condense ambient humidity — commonly reach 70–80% RH in summer even in dry-looking conditions. A 50-pint or 70-pint dehumidifier running continuously, emptied daily or connected to a floor drain, maintains basement RH below 55% in most Toronto basements. The Frigidaire and hOmeLabs dehumidifiers are widely available at Canadian Tire and Home Depot in Toronto.
Air Conditioning
Air conditioning dehumidifies as well as cools — the evaporator coil cools the air below its dew point, causing moisture to condense and drain away. Running AC during humid summer days reduces indoor RH significantly. The limitation: at night or on cooler humid days when AC isn't needed for cooling, humidity can climb again.
Bathroom and Kitchen Ventilation
Showers and cooking are the primary indoor humidity generation sources in most Toronto homes. Running the bathroom exhaust fan during every shower and for 20 minutes after, and the range hood during and after cooking, removes these moisture loads before they distribute throughout the home. In Toronto condos where bathroom fans are under-powered or poorly maintained, this is particularly important to enforce.
Addressing Moisture Sources
- Foundation seepage: Water seeping through basement walls is a direct moisture source that no amount of dehumidification can fully compensate for — addressing the source (exterior waterproofing, parging, drainage improvements) is required for severe cases
- Crawl space: Homes with crawl spaces in the Toronto area should have polyethylene ground cover over the crawl space floor — uncovers soil in a crawl space evaporates moisture directly into the house
- Indoor plants: Large collections of indoor plants contribute to indoor humidity through transpiration — not a dominant factor but a contributing one in humid-weather months
Cleaning After Humidity Events
After a period of high indoor humidity (basement flooding, an AC failure during heat wave, or simply a summer of above-average humidity), cleaning should include: wiping all window sills and frames (condensation runs down to these surfaces and creates mould conditions), checking behind furniture against basement walls (dead air pockets are the first places mould establishes), and scrubbing bathroom grout (elevated humidity accelerates mould in grout). Book a Maidless deep clean at maidless.ca/ontario. HST 13%, 4.9★ rated Toronto cleaning.