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In late September when the weather started cooling down here in Surrey BC Canada, we started to see morning condensation on our windows (newly installed last year):

Bedroom windows

My wife and I and our son sleep in the room, so presumably it is due to our breathing. I should double-check the humidity in the room when it happens again tomorrow, but I think it is about 60%. We do have a dehumidifier, but we find it too noisy to run during the night (even with a timer), so we just run it after we wake up.

Questions:

  1. Is the humidity/condensation in the windows and walls a concern for mold growth, or is it sufficient to run the dehumidifier after we wake up and rely on the sun to dry up the windows?
  2. How to prevent excessive humidity/condensation in the bedroom? It is cold, so we don't want to leave our windows partially open all night. And the dehumidifier is too noisy for us to run during the night. Would a silent moisture absorbing product like DampRid help? I heard that it won't help much.

I read that the key to solving humidity problems is improved ventilation. But how to improve ventilation in a bedroom with a closed door? The bathroom fan won't help because the door is closed. Opening a window won't work because it is cold outside. Is our only option an expensive Heat Recovery Ventilator that will vent to the outside while conserving heat? But aren't those as noisy as a dehumidifier?

I saw a similar question here (Why does significant condensation gather on my bedroom windows overnight?) but it just suggests opening the windows, using a dehumidifier, keeping the blinds open, putting bubble wrap on the windows (won't solve moisture getting into the walls though), and not worrying about it.

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Indoor humidity levels are high in the fall, making window condensation more likely. Where I am, we have to wipe our windows each morning for the first few weeks of cold weather. After that, it's less of a problem. It's important to exhaust moist air using bathroom and kitchen fans to reduce this effect.

Mold is a slight concern, but not as much so as during warmer months. More of a concern is liquid water damage. If water collects on the sills the wood will begin to swell and decay and the finish will degrade. This is your primary concern. If you wipe them each morning you'll mitigate the problem.

If you still have regular condensation a few weeks down the road, look into the source of the moisture and whether you can improve ventilation or room-to-room air mixing (possibly using a fan-only cycle on your HVAC system). The appropriate indoor relative humidity level depends on the outdoor air temperature, so it needs to decline during colder weather.

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Don't over look the possibility the windows were installed incorrectly. If they are bowing any or otherwise out of alignment, there could be just enough room for outside air to get in around seals. You may not even be able to see any misalignment.

I'd suggest using isherwood's answer first and if it's still a problem later, consider having the installation inspected/double-checked in case there's something wrong.

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