Why glass sweats in January
Water vapour can condense when moist indoor air meets a sufficiently cold window surface. The indoor humidity and the surface temperature both matter. Newer high-efficiency windows can still show edge condensation when humidity is high and outdoor temperatures plunge.
Ventilation’s role
Kitchens, baths, and crowded rooms add moisture. Bath fans that actually exhaust outside—not into the attic—help. In very tight homes, an HRV/ERV can exchange air without dumping all your heat.
Humidifier settings in winter
Adding moisture with a whole-home humidifier can worsen condensation. A humidity setting that works in milder weather may be unsuitable during a cold spell. Ask a technician to review the humidifier, ventilation and building conditions together rather than applying one fixed setting throughout winter.
Building envelope clues
Persistent condensation on walls or sills can indicate insulation gaps or failed seals. HVAC adjustments cannot fix all envelope problems.
When to escalate
Mold on drywall, rotting sills, or ice dam patterns tied to attic bypasses need building-science review alongside HVAC tuning.
Record where and when moisture appears
Before an assessment, note which windows are affected, the time of day and whether the moisture follows cooking, showering or a weather change. Record indoor temperature and humidity readings if you already have a suitable meter. Photograph the location of the moisture and any staining so the assessor can distinguish a recurring pattern from a single event. Do not treat a photograph or one humidity reading as proof of a failed window or a ventilation defect.
Make clear whether the moisture is on a surface you can wipe or appears elsewhere in the window assembly. Describe any nearby leak or damaged finish as a separate observation. This helps frame the investigation without prescribing a repair before the cause has been assessed.
Reduce moisture accumulation while arranging help
Health Canada’s moisture and mould guide recommends using kitchen and bathroom exhaust, allowing warm air to reach windows, keeping heating vents unobstructed and drying wet frames and sills. Heavy window coverings can restrict circulation at the glass. Check that furniture and coverings are not blocking the intended airflow; do not block vents to hide a cold draft.
Address known leaks promptly. If moisture returns despite ordinary ventilation and housekeeping, ask for a building assessment rather than repeatedly changing thermostat or humidifier settings. Recurring mould, suspected hidden damage or uncertainty about the moisture source warrants qualified help. Cleaning a visible mark alone does not resolve the cause of an ongoing moisture problem. Keep observations and any repair records together for the person investigating it.
Ontario climate context
GTA winters combine damp lake-effect days with dry Arctic highs. Your HVAC system should handle both without constant thermostat battles. Seasonal maintenance catches small issues—dirty flame sensors, weak capacitors, drifting charge—before they become no-heat calls on the coldest night. Canadian Smart Savings focuses on honest recommendations: sometimes a repair is right; sometimes replacement is safer or more economical over five years of ownership.
Working with a licensed contractor
Refrigerant handling, gas piping, venting, and electrical work are regulated for good reasons. Always verify licensing and insurance, and keep permits and inspection paperwork for resale. If something in this article conflicts with your equipment manual, follow the manual and ask your technician.
This article is general information only and is not a substitute for an on-site assessment by a qualified HVAC technician for your specific home, equipment sizing, combustion safety, or refrigerant work.
For maintenance, upgrades, or diagnostics in the GTA and surrounding areas, contact Canadian Smart Savings.