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- Winter humidity
How much humidity can your house actually take?
A dry winter makes a house uncomfortable; too much moisture puts water on the coldest surface in it. The ceiling is set by your windows and by the weather outside, not by preference.
The check
The figure is an estimate: the glass temperature is worked from the glazing type rather than measured, and one cold corner of the house can be worse than the windows. Treat it as a ceiling to stay under, not a target to hit. It runs in your browser and nothing is sent anywhere.
Keep indoor humidity below
35% at this outdoor temperature, with these windowsAt this point the house cannot carry much moisture at all. Running a humidifier hard here puts water on the glass and, worse, inside the walls around it.
- Turn the humidifier down, or off, on the coldest nights — many have an outdoor sensor that should do this automatically.
- If the air still feels harsh, the answer is usually warmer surfaces rather than wetter air: window coverings, draught sealing, or better glazing.
- Watch the coldest room. It reaches the limit before the rest of the house does.
A normal Inland Northwest winter figure. Comfortable enough for most people, and low enough that a reasonably built house stays dry.
- Set the humidifier to this ceiling rather than to a number somebody quoted you.
- Check the windows on the coldest morning of the week — condensation appearing is the signal to drop it a few points.
- Keep bathroom and kitchen extraction working; that is where most of the moisture arrives in the first place.
Mild weather or good windows, or both. The house can carry more moisture without complaining, which is why humidity problems here usually appear on a cold snap rather than on an average day.
- This ceiling will fall as the temperature drops — set the humidifier for the cold nights, not for today.
- A control with an outdoor sensor does that automatically and is worth having if you are fitting one.
- If windows fog at this level, something in the house is adding far more moisture than expected.
Where this stops being useful: a house with damp in a crawlspace or a leak somewhere is not a humidity setting problem, and no thermostat setting fixes it. If glass fogs with the humidifier off, that is what to look for.
The three kinds of humidifier, briefly
- BypassSimple, cheap, fitted across the furnace. Needs the blower running to do anything, and needs its pad changed every season.
- PoweredHas its own fan, so it works whenever it is called for. More output, more to go wrong, and still needs servicing.
- SteamMost output and most control; the most expensive to buy and to run. Usually only justified in a large or very dry house.
- The control matters moreA humidistat with an outdoor sensor lowers the target as it gets colder. Without one, somebody has to remember — and nobody does.
