I have a new home (less than 3 years) three stories and 2 hvac units. One is a forced air that handles the basement and first floor, the second is a heat pump that handles the second floor. I have found over time that when the upstairs unit and downstairs unit run at the same time it creates a draft that pulls under the doors that could put out a match. The units also appear to pull a strong draft from the basement door. Is my house this leaky or are my units pulling too much air? I am tired of being cold in the winter with a draft that only exist when the units are on.