It is the duct leakage and air leakage caused by supply and return pressure
imbalances that cause increased air change rates in forced air houses. Two
buildings could have the same blower door equivalent leakage areas, but
different actual leakage rates due to the driving forces of the HVAC
equipment, if the ducts leak and/or there are pressure imbalances. Forced
air systems don't dry air except through leakage.
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