Why is water heater going out when attic fan turned on.?

Question

Somehow when the attic fan sucks air up into the attic, it is making its way back down through the flu ducting of the water heater and furnace, even blowing out the pilot light on the water heater. The flue pipes run inside a chimney and we can't figure out how this air is back-drafting down these ducts. You can feel a back-draft breeze through the ducts in the basement when the attic fan is on.

Answer 1

This is what is happening. When your attic fan kicks on, your home must be fairly tight and sealed up. For an attic fan to work properly and not overworked you need a source of make - up air coming into the house, otherwise the attic fan will pull air in from places you don't want it to - like your flue pipe. It is sucking air down from the chimney which runs to the top of your water heater, and down to the pilot light.

First put some weatherstrip on the basement door and maybe a threshold at the bottom. This will stop the pilot light problem, but now you have to allow some make-up air to enter your home to supply the suction to the attic fan. I would open a couple of windows, one on each side of the house, experiment to see if that is enough, if not open them further or open a couple more. It's hard on the attic fan motor if you don't allow some air to come in. It's like sucking on a straw with your hand over the other end.

Answer 2

Get a builder in.

You really need to sort  this out...

If air from the attic is getting to the water heater, then flue gases could be getting into the house....which can kill.

Answer 3

The way you describe it, sounds like a big fan in your ceiling to the attic, right?  That would properly be a whole-house fan, and then you certainly need to open up windows throughout the house to have it work effectively.  Basically, DON'T try to use it as an attic fan only with windows closed.

Otherwise, as ted.... says, you'll be sucking air down thru your chimney into and out your water heater, blowing the pilot out.  And not a good thing if the heater was running you'd be sucking the flue gasses thru your house.