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Old 02-21-19, 04:05 PM   #13
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Originally Posted by jeff5may View Post
There seems to be a misconception about relative humidity here. Your 35 degree saturated outdoor air contains less than 30% relative humidity at 68 degrees. It's all about dew point.
That is true but not the whole story. That 35* air is the low at night. What happens is that during the day it is in the 60s ish and the humidity averages around 70% but often as high as the high 80s. So that humid air during the day is very close to interior temps then as it cools down at night the cooler air can't carry the moisture so it creates dew on everything. Then in the morning everything is soaken wet and as it warms up the air picks up that moisture again.

So yes for a few hours at night everything is in your favor to lower interior humidity but for the majority of the day you can't make headway. Also this is why it's common for commercial properties like restaurants to run the AC at the same time as the furnace int he winter to heat but also dry the air.

So yeah if you look at the narrow point of the humidity % being high when temps are at their lows then yeah using air from outside will lower interior humidity but that time period is very short here. It warms up very quickly in the morning here. It's not uncommon to start out below freezing and end up at 80* after noon.
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