Water heater exhausting inside house

Question

I have this I think standard gap between water heater and chimney. Due to house being colder inside than outside in summer time, I think the pressure difference is not allowing the exhaust to go up the chimney. If I open a window it helps...really helps if I open sliding door and window but we can't do that when we are gone and I hate coming home to a house full of exhaust.

What do others do about this problem? I have thought about drilling a hole from the garage into that room and put a fan on a timer to run during the day when there is a pressure difference (note: doesn't happen at night when it's much cooler outside...we live in the mountains) to blow air into the room forcing it out the chimney. Thoughts?

Answer 1

What you've described is a very serious carbon monoxide hazard called chimney backdraft.

You likely need to explicitly provide a fresh air intake so that chimney stack can work properly.

That water heater room needs non-blockable fresh air source year-round ASAP. Two 4-inch holes or one 6-inch hole could potentially suffice.

Warm air from the burners rises out the chimney so fresh air from the outdoors is supposed to replace it.

That vent relies on your house's natural breathability. Your house, or at least this room in particular is unable to pull in enough fresh air from the outdoors to replace the hot air trying to escape out of the chimney.

Your other option would be to upgrade to high-efficiency units which have an active blower. However, you would still need to ensure that enough fresh air makes it to the burners.

Above all else, install a carbon monoxide detector in that room.

Answer 2

Proper venting of a gas appliance should have nothing to do with the temperature indoors or out: the exhaust gas is hotter than either of those. It should naturally rise (draft) up the chimney (or "flue") regardless of the indoor and outdoor temperature conditions. There's something more amiss here. Any kind of "helper fan" is a dangerous cover-up that avoids finding and fixing the real problem.

So long as the chimney is clear, there's an adequate source of make-up air, and the room is not under negative pressure, the draft should function as expected.

You mentioned summer time -- outdoors being warmer than indoors. That implies to me that you have air conditioning. I suggest you have a good look at that the blower and duct work in that system, especially the air return portion. If the blower is not able to draw air through the normal return path, due to the inlet grill being covered, an air filter being dirty, a cover panel being removed, etc then the blower may pull air out of its own room instead. This could create a negative pressure zone in that room -- and air may be drawn down through the flue.