Sam, I think those are mainly cases where you have like a deep litter or large open water pans from which the heat makes moisture evaporate more quickly. If the ventilation is working and the ceiling is properly insulated so that condensation doesn't build, the heat would only lower the relative humidity. In addition, if you've got intake valves placed low in the coop and exhaust valves high up, the stack effect created by the heat would increase ventilation.