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Dehumidifier in Winter?

Benedict Waters | Posted in General Questions on

I have a second home in Vermont (North East) that I recently resided adding 2″ of EPS foam as well. I can already feel how much “tighter” (cool during those hot summer months and keeping the daytime heat at night) the house feels so now I’m on to trying to make sure the air is OK in the house for us and the wall system.

I keep the setpoints on my thermastats (1st and second floor) at between 45 – 50 degrees when not there. I can monitor the temperature and humidity both in and outside

Ideally, should I try to keep the inside of the house at some humidity level in relation to the outside temperature? And if so where should I place the humidifier?

Any ideas would be appreciated.

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  1. Doug McEvers | | #1

    The tighter house will have more humidity in winter than before due to reduced infiltration. Ventilation air should be addressed first.

  2. Riversong | | #2

    Your title says "dehumidifier in winter" but your question refers to summer and asks about a "humidifier".

    Which is it? Which season? And why do you think you need more/less humidity?

  3. Benedict Waters | | #3

    "And if so where should I place the humidifier?" Yes I meant dehumidifier sorry.

    I'm only concerned with the upcoming Winter months right now. I noticed more moisture in the air when I was working up there last weekend. In the morning there was some condensation behind the shades on a few windows which I don't remember seeing before.

    I will need to introduce a more overall solution in the future for ventilation but for now I thought I would address the humidity by installing a thermastat with a humidity sensor and monitoring it.

  4. Riversong | | #4


    You should actually check the interior RH before deciding what to do about it. If you're finding window condensation behind closed shades then open the shades, since they keep the interior glass surface colder and encourage condensation.

    If you do use a dehumidifier, I would suggest setting it for 60% RH. If you have a normal 40% interior RH at 70°F and drop the temperature to 45°, the RH will rise to 98% and the dewpoint will be 45.5° which guarantees condensation. At 45° and 60% RH, the dew point will be dropped to 32°.

    Either place the dehumidifier in some central location with all the interior doors open, or wherever you're seeing the most condensation.

    But what any tight house needs is whole-house ventilation, which can be accomplished with a 24-hr programmable timer on the bathroom exhaust fan, with or without passive make-up air inlets (depending on the leakiness of the envelope). You won't have a healthy home unless its ventilated.

  5. Benedict Waters | | #5

    Thanks Robert,
    That's the scenario I was trying to think about.
    -House is at 45 degrees
    -House rises to 65 degrees for a few days
    -House drops back to 45 again

    Average Winter month temp is ~18 I thought that if I got the humidity down which would lower my dewpoint on the sheathing I would be relieving some stress on the house. I'm looking at the exhaust fans now.

    Thanks for the help

  6. Anonymous | | #6

    do i need a dehumidifier in winter with no heat it a summer hang out log cabin in ky.

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