Just got the 2nd msg about heater types.
If you use propane heat in your house without exhausting the gasses outside, a direct vent model, this is 100% your problem.
If you use wood fire as heat it will be not likely to cause an issue.
The reason most heaters actually raise humidity is because the main byproducts of combustion are carbon, oxygen, and h20 (water.)
Propanes main byproduct in high efficiency units is water.
This next one is harder to grasp.
The reason you get higher RH in warmer temperatures is because the air molecules have a greater potwntial to hold moisture in the air.
This is why temperature is soooo important for RH and not many people go into it.
50% RH at 50 degrees F is not the same amount of water in the air as 50% RH at 90 degrees F, it is way less. I cant really explain it more simply or in depth without making my eyes cross. Just know that in actuality you have been fooling yourself by going only by RH.
Found a nice table to demonstrate.
Temp. Water holding capacity of vapor in grams
As you can see the holding capacity is not a lineqr function snd is actually a bell curve. Meaning the rate of water holding capacity does not increase evenky with temperature, it exponentially holds more moisture.
Talk from anyone from alabama or brazil they will confirm hot does not reduce moosture in air…it makes it horrible.