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What do recurring frost patches in window corners point to?
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When frost keeps forming at the inside corners of a window, what observations help sort out cold glass from air leaking around the sash or frame? Does it matter whether the frost stays on the glass or also shows up on the sash and frame?
I’d also like to know how much the pattern changes with indoor humidity and the window’s surface temperature. Would frost on a still, very cold night, without an obvious draft, tell you anything useful, or is it hard to interpret without checking the window more closely?
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