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My home is a single level ranch style. All new windows that are less than 4 yrs old. It has base board heating. During the cold season, when the heat is on, there is an extreme excess of condensation on the inside of the windows in most rooms. In one bedroom, where there is a large bay window and small sliding window, I frequently find pools of water at the base of the bay window. Even the ceiling in one side of that room occasionally has droplets of water in about an area of about 1 foot and shows speckles of mold. I clean using a bleach solution but it comes back every month. This is the worst room in the house.

I have checked the insulation in the attic and it is sparse. Even the walls adjacent to the exterior are cold to the touch in the winter. I have 3 to 3 hanging bags of "Damp Rid" in the room but the problem persists. I have used a Dehumidifier in the past but it really drives up my electric bill.

My question is why is there so much condensation happening? What can be done to prevent or reduce it? Thank you for the feedback.

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    What part of the world do you live in? When was your house built? Does your house have a ventilation system? Are there any unusual sources of moisture in your house? Fish tanks, cooking pasta a lot, long hot showers, etc. – iLikeDirt Dec 10 '15 at 23:58
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    Are the windows single-pane, single-pane with storm windows, (& are the storm windows closed, in that case) double-pane...? – Ecnerwal Dec 11 '15 at 0:10
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You get condensation because the windows (and evidently part of the ceiling, unless that's just a roof leak) are the most poorly insulated part of the building, so they cool below the dewpoint of the interior air.

Bay windows are particularly bad as they are a fairly large expanse of window stuck out into the cold, and not infrequently the non-window parts of the bay are not well-detailed from an insulation point of view. They also have a lot of joints making potential cracks to leak cold air.

Active ventilation can help remove some of the interior moisture (from whatever sources), but since your investigation has shown poor insulation, solving poor insulation is probably a good idea as part of the overall fix.

  • If you happen to be using an unvented gas heater for your heat, that alone will add a huge (generally unacceptably huge) amount of water to the indoor air (and replacing it with a vented heater will help immensely.) Indeed, most houses are quite dry through the winter with normal heat, which is why I mention that, as I half-suspect it.
  • If you have a gas range and your range hood is either not running when you operate the range, or one of those useless range hoods that does not actually exhaust air (merely recirculating it through a filter) that will add water to the air.
  • Bathrooms without fans, or with unused or ineffective fans also add water to the air.
  • Improperly vented clothes dryers or hanging laundry to dry in the house add water to the air...

For a quick, inexpensive approach on the windows, consider using "window shrink film kits" for the winter. They effectively make an interior "storm window" and both reduce air leaks and radiative heat loss. If done carefully they don't look bad.

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