Does a house heating system affect indoor air humidity? Or to be more precise, does it affect your perception of how dry the air in the house feels (for instance dry is your mouth waking up)?
(I searched for this but could only find explanations from furnace company websites)
Every (lay)person I ask this seems to think house furnaces make the air drier (at least the perceived dryness). One friend claims that the air gets even dryer than the outside air.
My intuition is that heating can only increase the evaporation inside the house (from the little surface liquid water sources (shower, taps) there may be), therefore making humidity go up.
I suspect people think this because furnaces are only on in the winter when the outside air is dry leading to dry air inside as air exchanges. Thus it could be due to this spurious correlation.
Another possible explanation is that the higher air temperature increases the air's water carrying capacity, which in the absence of an abundant water source, extracts water from your body faster. Therefore increasing perceived dryness. Even if these two countervailing effects are true, can we use first principles to bund which effect dominates?
EDIT (after seeing the answers and discussions below): Perhaps perceived humidity is too loose to define. What if we define the water loss of a human over a period as our measure? But my ideal answer would have two numbers to compare:
- Baseline_loss = how much water does a person looses sleeping in a cold sealed room (say at 1C temperature) with 100% relative humidity and no air movement.
- Total_loss = how much water does a person loses if the same sealed room was heated up to 22C (a nice in-home temperature).
Then Heating_induced_loss = Total_loss- Baseline_loss