When it is cold: brief airing, keep the heat
In true cold, keep the heat you already paid for and air in short bursts. Then close. Take winter sun through closed glass. Skip long night airing when it is very cold.
In true cold, the job flips: keep the heat you already paid for, and air in short bursts. Outdoor air can still be worth a few minutes if it is dry and not extreme. Then close.
The app can still tell you when a brief opening makes sense, and when to harvest daylight through closed glass with blinds open. That is the opposite of a heatwave night flush.
The cold-weather checklist
- Air for a few minutes, then close; do not leave windows open
- Skip night airing when it is very cold
- Open blinds on sunny days while keeping the window shut
- Follow rain and wind: wet, bitter air is not a good airing
Minutes, not hours
Stale indoor air is still worth swapping. You do not need a cross-breeze that dumps the room temperature. Open, let the air change, close. Repeat later if the room feels stuffy.
Do not treat a sunny winter noon like a summer evening. Sun on closed glass warms the room. An open sash dumps that warmth into the street. See the same idea in continental winter and Mediterranean winter.
If the cold is also wet, keep the opening even shorter. See when it is cold and humid.
What Ventilate is not doing
This is not a CO₂ or mold product. It does not measure indoor humidity. It still uses indoor temperature, local weather, sun, and layout to rank whether a short opening is useful.
Compare indoor and outdoor temperature the same way as in summer. The threshold for “useful outdoor air” is just much shorter when you are defending indoor heat.
This is not medical advice. If cold or damp is making you unwell, follow your local health agency.