In a previous posting I mentioned running into an issue with our water heater failing to draft when all the exhaust fans and clothes dryer running. I did some research and through testing I thought the entire issue could be resolved by adding more “make-up air”. Thus I added a 6″ duct into our mechanical room. This was in addition to our existing 5″. You would think that after having ~48″ sq.

Over Thanksgiving I discovered a torrent of cold air pouring behind our shower in the basement and tracked it to a large opening in our attic. That same day I went and picked up some additional insulation and proceeded to close the opening. Problem solved right? Nope, instead I found out by sealing this rather large hole I made our home too tight. The problem is that in worst case testing (all exhaust fans running and the clothes dryer) a significant enough negative pressure was created which prevented our water heater from drafting correctly.