furnace is running
AJ is your furnace oil if it is it can suck the exhast

My air make unit is three 7 inch hole in the ceiling .I call it my poor mans air make up unit .It work great I ajusted the flow its pretty balanced IT NEVERE GET BELOW -3 CELIUS HERE.If your not carefully you can put a strain on your motor for the fan. Its like a straw sucking plug the hole or make the straw opening to big it doesn;t work properly

Thats why if your moving its important to do the research on a spay boths can be the most expensive investment in a cabinet shop/Did we mention spriklers