Condensation on Windows in Winter

Cold weather shows up on the glass. Beads, then a puddle on the sill, then a musty smell if the puddle sits in dust. Winter condensation is moisture from the house landing on a cold pane. It is common. It is also a message. The glass is not "leaking winter" in the way a failed roof leaks. The water started indoors, unless you can see rain coming through.

A gauge tells you how hard the glass is working. Read it in the morning in the room with the worst windows. Aim for under about 50 percent. If you are well above that, the panes will sweat when it is cold outside, even good panes. Lower the moisture you add. Bath fan during showers and 20 to 30 minutes after, ducted outdoors. Dryer vented outdoors and not blocked. Humidifiers turned down. Lids on boiling pots, range fan on. These are dull and they show up on the glass within days.

Wipe the sill every morning while you sort the source. Standing water is what stains wood and smells. The wiping is not the cure. It is how you avoid a rotten sill during the cure. If the wood is already soft, a carpenter needs to see it. Do not paint soft wood because company is coming.

Between the panes is different. Fog you cannot wipe from either side means the seal in a double pane has failed. That looks like condensation and it will not respond to a dehumidifier. The glass unit is the repair. Note it so you do not spend the winter "humidifying less" at a window that is fogged in the gap.

Storm windows and plastic film can reduce sweating on the inner glass and can also trap water if they are sealed badly. Look behind them. A hidden wet sill is worse than a visible one.

New windows are a real project when the frames are rotten or the glass has failed. They are a disappointing project when the house is simply wet and the new glass is still cold. Dry the habits first. If the gauge is reasonable and one old window still pours while the others are fine, that window is the candidate, not the whole elevation.

Do not vent a gas appliance or block combustion air in the name of humidity. Do not tape over a flue. Indoor air quality around burning appliances is a pro conversation if you are unsure. And if you smell gas, leave and call the utility from outside.

Write the morning number and which rooms wet the sill. A week of that, with the bath fan actually running, will tell you if this is house moisture or one bad pane.

Compare a bathroom window to a bedroom window on the same morning. If only the bath is soaked, stay on the fan. If every bedroom is soaked and nobody bathed, the house has another moisture source, often a humidifier, a dryer, or a wet basement sharing air. The worst window is the reporter, not always the culprit.

Keep curtains off the glass during the day so the pane can warm and so you see the sill. Condensation you do not see still drips. A quick hand on the wood each morning is enough to know if yesterday's wipe was the last one or the first of many.

When the cold snap ends, notice whether the glass goes quiet. If it does, you have a humidity and temperature story. If a sill stays wet in mild weather, look for a leak, not for another lecture about showers. Weather changes are free tests if you are willing to look.

If someone in the house is getting worse, that is a doctor conversation, and opening walls or the furnace cabinet is a job for a licensed pro.

Winter glass is a picture in When Your House Doesn't Feel Right. $2.99 at https://clearnestair.com/book.