Discussion Starter · #1 ·
I have a one-zone HVAC system in my two story house. The furnace and air-conditioning unit are in the basement. When I turn on the fan at the thermostat control, with both the heating and air-conditioning off, I can feel a strong draft under the door at the top of basement stairway. The draft stops when the fan is off. I don't understand the negative pressure in the basement when the fan is running in a closed duct system. Does that mean the duct leak on the return side is much greater, so the basement air is sucked into the duct system?