thankyou fan in a can.....
sprayfoamed insulated house as tight as tight can be,home owner disconnected carbon monoxide alarm as it annoyed him when it went off.sealed boiler room,200,000 btu boiler .fresh air was via a 10"x3" duct.i put a pieceof paper on boiler and it got blown back from chimney backdraft.our temporary solution was a 6" line from outside house into boiler room hooked up to fiel control cas-4 fan in a can.my first time using it and am very impressed.
Those can be a big help!
Outside combustion air is often needed, especially in the tight"energy efficient" homes. People need fresh air, too, and Energy/heat recovery ventilators work for them.