Humidity – Air moving from cold outside to warm inside ?
We are having a few issues in our new house including windows with very significant air leaks and extreme differences in humidity throughout the house.
Indoor humidity ranges from about 15% in the scullery hall next to the kitchen to 35% in the loft. Current values are:
Loft = 35%
UL Bedrooms = 21%, UL Master Suite = 29%
ML Living Rm = 24%, ML Kitchen/Scullery Hall = 15%
LL = 26%
The loft is basically a finished attic so we have 4 levels total. Temps range from 66°f – 69°f. I have verified that these are measuring humidity accurately w/ a Gaslab 501. They don’t appear to ever be off by any more than 1%.
We have two air handlers and fans run continuously so we should be getting good air circulation through the house.
Outside is -17°f and 55% RH.
It seems that two things are happening with RH. Thermostats with more window exposure and particularly more western window exposure seem to have much higher humidity. The Kitchen/Scullery Hall thermostat is the most protected from windows and consistently has the lowest humidity. Living Rm thermostat is exposed to a lot of west facing windows.
Just as hot air rises, so does water vapor? The 4th floor loft consistently has the highest humidity. Stack Effect? BTW, stack effect is very noticeable as LL windows have greatest air leaking through to inside, ML is next. UL you can’t feel much of anything and in the loft you can feel air moving outward. I’m guessing the neutral pressure plane is just above the ML windows.
HOWEVER, would air infiltrating through the windows (and you can feel a lot of it and in some cases see daylight between sash & frame) raise or lower the humidity in these rooms? My limited understanding is that air w/ 55% RH @ -15°f will have a lot less water in it than air of perhaps 20% humidity @ +7-°f. Correct? Or could this outside air be increasing the humidity?
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