Window Condensation in Winnipeg Winters: Normal Humidity or a Failed Seal?
The short answer: condensation on the room side of your window on a -25°C Winnipeg morning is usually a humidity problem and is fixable without replacing anything. Condensation or fog between the panes is a failed seal, and that unit needs replacing. Condensation on the outside of the glass is a sign your window is doing its job. This post explains each one, gives you the indoor humidity targets for Winnipeg temperatures, and tells you when moisture means it’s time to call us.
Every November we get a wave of calls that start with “my brand-new windows are sweating.” Sometimes that’s on us. Usually it’s physics. Here’s how to tell the difference, because we’d rather you know than guess.
Why Winnipeg windows sweat more than most
Warm air holds moisture. When it touches a surface colder than its dew point, the moisture drops out as water. The inside pane of a window is the coldest surface in any room, and in Winnipeg it is very cold: on a -30°C night, the inside of an old double-pane window can sit at 5°C or lower. Showers, cooking, laundry, a humidifier on the furnace, houseplants, and four people breathing all add moisture. The window is where it lands.
This winter is forecast to run milder than normal thanks to El Niño, with 80–89% odds of above-normal temperatures in Winnipeg. That actually makes condensation worse on some days, because people keep the humidifier up and the house tight while outdoor temperatures bounce around.
Three kinds of condensation, three different answers
1. Inside surface (room side): humidity
Water beads or frost along the bottom edge of the glass, worst in bedrooms and bathrooms, worst first thing in the morning. The glass is intact; you can wipe it. This is the common one. It tells you the indoor air is holding more water than the window surface temperature can tolerate.
The fix is to lower humidity, raise the glass temperature, or both. See the targets below.
2. Between the panes: failed seal
A hazy film, water streaks or droplets you can’t wipe from either side. The spacer seal has let go, the argon has leaked out, and moist air has moved into the gap. The window has lost most of its insulating value and the fog will get worse every winter. No amount of dehumidifying helps. The sealed unit (or the whole window, if it’s old) has to be replaced. Our post on the seven signs it’s time to replace your windows ranks this near the top.
3. Outside surface: good news
Dew or frost on the outside of the glass on a cool, humid morning, usually in fall or spring. It means the outer pane is cold because almost no heat is escaping through the window. This is what a well-performing triple-pane unit does. It burns off by mid-morning.
Indoor humidity targets for Winnipeg temperatures
These are the numbers we give every customer, based on the standard window-condensation guidance used across Canada. Set your furnace humidifier or a hygrometer ($15 at any hardware store) to these levels:
| Outdoor temperature | Max indoor relative humidity |
|---|---|
| -10°C | 40% |
| -20°C | 35% |
| -30°C | 25–30% |
| -40°C with wind chill nights | 20–25% |
Yes, 25% feels dry. That’s the trade-off in January. With triple-pane windows you can run 5–10 points higher at the same temperature because the inside glass stays warmer.
Ten ways to cut room-side condensation this week
- Turn the furnace humidifier down (or off) once it drops below -20°C.
- Run the bathroom fan for 20 minutes after every shower. Put it on a timer switch.
- Use the range hood whenever a pot is boiling, and vent it outside, not into the cabinet.
- Open blinds and curtains during the day so warm air reaches the glass. Heavy drapes trap cold air against the window and make it worse.
- Move houseplants off the sills.
- Check the dryer vent is connected and clear.
- Run the HRV on continuous low if you have one.
- Keep furniture a few inches off exterior walls so air circulates.
- Crack a bedroom door at night; closed rooms with sleeping people hit the dew point first.
- Wipe the sills every morning while you fix the cause. Standing water rots wood and feeds mould.
When condensation means the window itself is the problem
Call us if any of these show up:
- Fog between the panes (failed seal).
- Ice that builds on the inside glass even at 30% humidity. The glass surface is too cold, which usually means single pane, no low-E, or an empty argon gap. Our guide on stopping ice buildup on windows covers this.
- Water in the frame corners or black staining on the wood or drywall below. That points to a leak around the frame, not on the glass. See drafts around newly installed windows.
- Condensation on only one window in a room full of similar windows. Something is wrong with that unit.
On a replacement, we foam and tape the rough opening, set the unit square, and use Energy Star triple-pane glass with warm-edge spacers. The spacer is the detail most people never ask about; a warm-edge spacer keeps the glass edge several degrees warmer, and the edge is where condensation starts. Learn more on our triple pane windows page and our window replacement service page.
Our own lesson, in the open
A few winters ago a customer in the north end replaced windows with us specifically to stop condensation, and the new units still showed moisture the first cold week. We went back. The home had a furnace humidifier set to 45% and no bathroom fan. We adjusted the humidifier, installed a timer fan, and the problem was gone in two days. That job changed how we do handovers: every install now ends with a humidity check and this table on the fridge. Our Google reviews include both the happy endings and the lessons, and you can find us on our Google Business Profile.
Frequently asked questions
Do new windows cause condensation?
New windows are tighter, so they trap more moisture inside the house. They reveal a humidity problem that old leaky windows were masking by venting it outdoors. Lower the humidity and it stops.
Is window condensation dangerous?
The water itself isn’t. The mould it feeds on sills, drywall and blinds can be, and it rots wood frames over a few winters.
Can a failed seal be repaired?
The sealed glass unit can sometimes be swapped if the frame is sound and under 15 years old. Older vinyl or wood frames are usually worth replacing as a whole.
Why only on the bottom of the glass?
Cold air sinks inside the gap and the frame edge conducts more heat than the centre of the glass, so the bottom corners are always coldest.
Not sure which kind you have?
Send us a photo or book a free visit: (204) 318-6162 or request a quote. We’ll tell you straight whether it’s the air in your house or the window in your wall.
Related reading: Common window problems in Winnipeg · What are Low-E windows? · Winter 2026 window rebates
