Do Outdoor Temperatures Affect Indoor Humidity Levels?
Indoor air humidification is essential to maintaining an optimal RH in cold climates.
Admitting cold outdoor air into a space will lower the indoor RH. When the lower temperature outdoor air is brought indoors and heated, it loses moisture and reduces the overall RH.
For example: if the outdoor temperature is 0°F and 50% RH and the air comes indoors and is heated to 70°F, the residual moisture after heating the outdoor air will only be about 3% RH. Even on a nice, sunny 35°F and 50% RH day, the residual indoor RH will only be about 14%.