High indoor humidity makes your home feel stuffy, speeds up mould growth, and damages wood, drywall, and window frames. To reduce humidity in a room naturally, improve ventilation, fix moisture sources, use hygroscopic materials like rock salt or baking soda, and keep windows working properly so moist air can escape. Most Canadian homeowners can bring relative humidity (RH) down to the recommended 30–50% range without a dehumidifier.
Why indoor humidity gets too high
Ontario homes are especially prone to moisture problems. Humid summers push outdoor RH into the 70–80% range, while winter heating traps condensation on cold surfaces — particularly around older windows.
Common causes of excessive indoor moisture include:
- Cooking without an exhaust fan running
- Long or frequent showers in poorly ventilated bathrooms
- Drying laundry indoors on racks
- Gas appliances that release water vapour during combustion
- Crawl spaces or basements with exposed soil
Leaky or single-pane windows also allow warm, humid air to condense on the glass and frames, wicking moisture into surrounding walls. If you’re seeing condensation regularly, it may be time to consider double or triple-glazed window replacement before addressing the humidity on its own.
Natural methods to lower room humidity
1. Open windows strategically
Cross-ventilation is one of the fastest ways to flush moist air out of a room. Open windows on opposite sides of the house to create airflow — even 10–15 minutes can reduce RH noticeably on a dry day.
The catch is timing. In summer, outdoor air in the GTA can be just as humid as indoors before noon. Open windows in the early morning (before 8 a.m.) or after sunset when outside RH tends to drop. In winter, outdoor air is cold and dry — even a brief airing-out pulls moisture out quickly.
Operable window styles make a real difference here. Casement and awning windows open fully and catch side breezes that sliding windows cannot. Awning windows can stay open during light rain, allowing ventilation even in wet weather without letting water in.
2. Use rock salt or silica gel
Rock salt (sodium chloride) is a hygroscopic material — it pulls moisture from the air and holds it. Fill a plastic container with coarse rock salt and leave it in a damp corner, basement, or enclosed room. Empty the collected water and refresh the salt every few weeks.
Silica gel packets work the same way on a smaller scale. Recharge them by baking in an oven at 120°C for 1–2 hours.
3. Ventilate when cooking and showering
Running your kitchen range hood and bathroom exhaust fan during and for 20 minutes after cooking or showering removes the biggest single-event moisture spikes in most homes.
If your bathroom has a window, a hopper-style basement or bathroom window keeps it open safely even when no one is home.
4. Fix leaks and seal gaps
A slow drip under a sink or a cracked foundation wall can add litres of moisture to your indoor air every day. Check under sinks, around the water heater, and at window frames for signs of water intrusion.
Gaps around window frames are particularly problematic. Failed caulking or worn weatherstripping lets moist air in while also reducing your home’s energy efficiency.
5. Use indoor plants selectively
Some plants actually increase humidity by transpiring through their leaves (snake plants, ferns, peace lilies). In a damp room, swap them out for low-transpiration species like cacti or succulents, which absorb moisture rather than add to it.
6. Spread moisture-absorbing materials
Place bowls of baking soda in closets, bathrooms, or any room where air circulation is low. Baking soda absorbs modest amounts of moisture and also neutralises musty odours. Replace every 30 days.
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How windows affect indoor humidity
Poor-performing windows are often the root cause of chronic moisture problems in Canadian homes — not just a symptom. Here’s how different window types compare from a moisture-control standpoint:
| Window type | Ventilation control | Condensation risk | Best use |
| Casement | High (full open) | Low (warm edge glass) | Living rooms, bedrooms |
| Awning | High (stays open in rain) | Low | Bathrooms, kitchens |
| Double-hung | Medium (top & bottom open) | Medium | General use |
| Fixed / picture | None | Medium–High (single pane) | Views only |
| Slider | Medium | Medium | Bedrooms, family rooms |
Upgrading to ENERGY STAR™ certified windows with Low-E glass, argon gas fill, and warm-edge spacers keeps interior glass surfaces warmer — which is the main reason condensation forms in the first place. Cold glass surfaces act like a cold drink on a summer day: moisture in the air condenses on contact.
Homeowners in Brampton and the broader GTA often notice condensation disappear almost entirely after replacing old single-pane units. If you’re in the area, window replacement in Brampton is worth exploring before spending money on mechanical dehumidifiers.
Sandra Kowalczyk, RHI (Registered Home Inspector), Ontario Association of Home Inspectors: “In my experience, chronic high humidity in Ontario homes almost always traces back to two things: inadequate ventilation and windows that no longer form an airtight seal. People spend money on dehumidifiers when the real fix is caulking the frame or replacing the unit entirely. A sealed, thermally broken window keeps the glass surface warm enough that condensation simply doesn’t have anywhere to form.”
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Ideal indoor humidity targets by season
Ontario’s climate swings from very dry winters to very humid summers. Indoor RH targets should shift accordingly:
| Season | Outdoor temp range | Recommended indoor RH |
| Winter | −20°C to 0°C | 25–35% |
| Spring / Fall | 0°C to 15°C | 35–45% |
| Summer | 15°C to 35°C | 45–55% |
Keeping RH above 30% in winter prevents static electricity, dry skin, and cracking wood floors. Staying below 55% in summer keeps mould from taking hold on walls, window frames, and caulking.
Marcus Osei, Building Science Technologist, Ontario Building Envelope Council: “A lot of homeowners focus on dehumidifiers, but the building envelope is where the real work happens. If the window system has thermal bridging at the frame — which is common with older aluminium or early-generation vinyl units — you’ll get condensation at the perimeter regardless of how low you push indoor humidity. Warm-edge spacers and multi-chamber vinyl frames eliminate that bridge.”
Rooms that need the most attention
Different rooms produce moisture at very different rates. Prioritise natural humidity control in this order:
- Bathroom — showers produce the most single-event moisture
- Kitchen — cooking, dishwasher steam, and kettle use all add up
- Basement — ground moisture migrates through concrete; use rock salt or silica gel and ensure any windows are properly sealed
- Laundry room — always vent your dryer outside; never indoors
- Bedroom — breathing adds about 1 litre of moisture to indoor air per person per night; keep a window cracked when possible
For basement windows specifically, hopper-style basement windows are the most practical option — they open inward at the top for controlled ventilation while staying protected from debris and pests.
When natural methods aren’t enough
Natural humidity control works best in well-built homes with modern windows and no active water leaks. If you’ve done everything on this list and still see RH above 60% consistently, you likely have a structural moisture source — a wet basement, leaking roof, or failed window flashing.
At that point, a mechanical dehumidifier or an HRV (heat recovery ventilator) paired with new windows is the right answer. An HRV brings in fresh, dry outdoor air and exhausts stale, humid indoor air without wasting heat — a standard feature in new Ontario builds since the 2012 Ontario Building Code amendments.
If your windows are more than 15–20 years old, condensation on the glass, visible seal failure (fogging between panes), or draughts around the frame are signs the unit needs replacing. Replacement casement windows or tilt-and-turn windows with ENERGY STAR™ certification and triple glazing will do more for your indoor comfort than any number of rock salt bowls.
You’re welcome to visit our showroom or get in touch with our team to find out which window upgrade makes the most sense for your home.
FAQ
What is the fastest natural way to lower humidity in a room?
Open windows on opposite sides of the room to create cross-ventilation. On a drier day, this drops relative humidity noticeably within 15–20 minutes without any equipment.
What humidity level is too high indoors in Ontario?
Above 60% relative humidity year-round risks mould growth on walls and window frames. In winter, keep indoor RH below 35–40% to avoid condensation on windows and cold surfaces.
Does opening windows always reduce indoor humidity?
Not always. In summer, outdoor air in the GTA can be just as humid as indoors. Open windows in early morning or after sunset when outdoor humidity is lower for better results.
Can old windows cause high indoor humidity?
Yes. Failed seals, thin glass, and aluminium frames create cold surface temperatures that trigger condensation. This adds moisture to wall cavities and surrounding materials over time.
How do I know if I need a dehumidifier or new windows?
If condensation appears only on window glass and frames, upgrading to ENERGY STAR™ certified windows with warm-edge spacers is usually the more effective fix. A dehumidifier treats symptoms rather than the source.
