Replacing window fin-pile seals to reduce condensation?
I have vinyl-frame double hung windows throughout my house. Installed in 2006. When it gets cold outside, condensation accumulates at the lower edges/corners, and where the two sashes meet. When it gets REALLY cold, I have seen ice at those spots. You can also see some mold spores in the photos.
The seals I believe are called “finned pile” style seals. Could I / should I replace these with rubber compression gaskets or another style of sweeps?
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I'm not familiar with the term "finned pile seals." While it seams that you are speculating that the cause of the condensation is air leakage through leaky weatherstripping, that may not be the case. You may simply have a humid house and cold windows. (At least one of your photos shows condensation that is nowhere near the weatherstripping.)
You can test the weatherstripping by holding a stick of incense near the cold areas of your windows. If you have air leakage, the incense stick will show it.
If you have ordinary window condensation, there are only two ways to limit it: either lower the indoor relative humidity (in winter, this is done by operating your mechanical ventilation system more frequently), or increase the temperature of the glass (by adding storm windows or keeping the curtains open).
For more information, see "Rating Windows for Condensation Resistance."
Yes, leaky weatherstripping is my hypothesis. I found the term "finned pile seal" here: http://chicagowindowexpert.com/2015/01/06/window-weatherstrips-gaskets/
The author states that bulbs seal better than fins or sweeps:
"All other operable window types utilize compression weatherstripping, such as bulbs or fins. These tend to seal better that sweep-type window weatherstrips because they are actually compressed between sash and frame when the sash is locked in the closed position. "
As far as controlling the indoor environment, there are no curtains over the windows to trap warm air. No mechanical ventilation system in the house (beyond the furnace fan). Currently heating with just the woodstove, haven't turned on propane furnace yet.