"sweaty windows" I wondered whether this had anything to do with computers...

"moist heat" - Hydrogen from the hydrocarbon fuel combines with Oxygen in the air to burn and produce H2O - water - the carbon -> CO2. Coal or coke fires produce less water vapor than wood or gas fires.

The old wood stoves (which vent outside) produce 'dry heat' - they elevate the temperature thus reducing the humidity. Humans need some humidity, totally dry air is not good for us and can promote illness - so one often has some water boiling on the old wood stove.