Originally posted by fourth year:
You do not have a problem when the burner is operating, so unless you also installed a damper in the flue, which would be illegal under a lot of codes, a blower would not help your problem. You have an illegal flue, since it is supposed to rise to a point above the roof line, but in any case not terminate through a side wall. Do you have a Belmont cap on the flue and a draft diverter on the water heater?
I don’t know what the Belmont cap or the draft diverter is? I have a standard cap on the outside wall that prevents rain from getting in the top. The top of the heater has a adapter that is wider than the ehaust ducting, I think this is standard. I had asked the inspector about exhausting on the side wall and they approved it. May be they did not know that this should not be done.
If the burner is operating and there is some back flow, I believe some of the exhast gases may be coming in the house until the flow reverses after about 5 minutes or less.