Condensation on Windows: Causes, Fixes, and When to Call Pros This Winter

January’s cold snaps in Toronto and across the GTA make window condensation a daily nuisance. You wake to fogged glass, damp sills, and even black spotting on caulk lines. Beyond being annoying, persistent moisture can damage frames, encourage mould, and make rooms feel colder. Here’s how to understand what’s happening, the fast fixes that work in our climate, and when to call Perfect Window and Eaves Cleaning Inc. for professional help.

Why are my windows wet in winter?

Condensation forms when warm, humid indoor air hits the cold glass surface and cools to its dew point. In Toronto winters, glass can drop well below room temperature, especially on older single‑pane or leaky double‑pane windows. Holiday hosting adds to the problem—more cooking, showers, and laundry elevate indoor humidity. Closed blinds, blocked heat vents, and air leaks around frames all make glass colder and increase moisture.

Common culprits in GTA homes and condos

High indoor humidity: Long showers, simmering pots, and drying clothes inside add moisture quickly, especially in smaller spaces.

Cold glass and frames: Poor insulation, failed weatherstripping, or heavy drapes pressed against windows lower surface temperatures.

Restricted airflow: Furniture, blinds, or sealed-off vents prevent warm air from washing over the glass.

Window system issues: Blocked weep holes, deteriorated exterior caulking, or failed double-pane seals lead to recurring fog and damp sills.

Quick fixes to reduce window condensation now

Use exhaust fans: Run bathroom and kitchen fans for 20–30 minutes after showers and cooking. In newer homes, set the HRV/ERV to continuous low.

Lower humidity: Aim for 35%–40% relative humidity at 20–21°C. Use a portable dehumidifier during cold snaps or in basements.

Improve airflow: Open blinds a few inches, lift drapes off sills, and ensure heat registers are unobstructed.

Add gentle circulation: A quiet fan on low helps move warm air across glass in problem rooms.

Seal small drafts: Replace worn weatherstripping and caulk minor gaps around trim to reduce cold air infiltration.

Maintain sills and tracks: Wipe moisture each morning to prevent staining and mould; keep weep holes clear so water can escape.

When condensation signals a bigger problem

Persistent puddles or mould growth on frames and drywall

Peeling paint, swollen sills, or soft wood

“Fog” trapped between double panes (failed IGU seal)

Drafts or visible gaps around frames despite weatherstripping

Ice forming on the interior of windows during deep freezes

In these cases, professional servicing is recommended. While replacement may be necessary for failed glass units, many issues respond to targeted maintenance, detailed cleaning, and better drainage around the home.

How our services help Toronto homeowners this winter

Interior and exterior window cleaning: We remove residue, mineral film, and biofilm that hold moisture, detail frames and sills, and clear weep holes so water drains—not pools. Clean glass also makes condensation easier to manage and spot early.

Eavestrough cleaning and repair: Ice dams and overflowing gutters chill the eaves and window surrounds, creating colder interior glass near exterior walls. We clear debris, flush downspouts, correct pitch, and install leaf guards to improve winter drainage.

Caulking touch‑ups and minor odd jobs: We can re‑caulk small gaps at trim, adjust sticking windows and doors, and free blocked vents or registers that reduce airflow to problem panes.

Power washing and exterior care (seasonal): When temperatures allow, exterior cleaning removes grime and salt that degrade seals and finishes.

Condo considerations across the GTA

Many Toronto condos run warm but trap humidity. Use kitchen and bath fans, avoid drying clothes indoors, and keep air pathways open around windows. We’re experienced with condo guidelines—booking service elevators, protecting common areas, and using low‑odour, condo‑safe products for interior window cleaning and minor caulking.

Preventive habits for the rest of winter

Ventilate after gatherings: A brief air exchange on milder days resets indoor humidity without chilling the home.

Monitor with a hygrometer: Keep one on each level to catch spikes.

Schedule maintenance: Clean windows and gutters in late fall or mid‑winter thaws to maintain drainage and reduce cold‑edge issues.

Your local partner for a clearer, drier view

Perfect Window and Eaves Cleaning Inc. brings 20+ years of experience to homes and businesses across Toronto and the Greater Toronto Area. We combine meticulous window cleaning with practical maintenance—eavestrough service, minor sealing, and helpful odd jobs—to reduce condensation risk and protect finishes. Our team provides free on‑site estimates, follows strict safety protocols, and ensures 100% satisfaction with a post‑service follow‑up.

See clearly this winter—without the worry

Book your January service today. We’ll assess problem windows, recommend smart fixes, and deliver spotless glass, clean sills, and improved drainage so you can enjoy a brighter, healthier home. Visit perfectwindowcleaning.ca to schedule across the Greater Toronto Area.