This is absolutely true. Have had customers come to me and say their chimney is messed up and their wood is back drafting. So I go to investigate and the stove is working fine until the HRV comes on, I know they’re supposed to replace the vented air with an equal amount of fresh air but that only if the guy that installed it has dialed it in properly. Or a kitchen fan or bathroom. The way houses are sealed up now a wood stove installation needs a fresh air intake located somewhere near the stove to supply the draft in the chimney. But I don’t think Fred’s shop will be that sealed up and at -30 when he uses the fan he shortly know where all the air leaks in his shop are.