downdraft problme on my 90 HEF

Empire_2

That's good to know. I haven't heard of that practice. I guess all the manufacturers have their own specs...

Tom_68

downdraft problem on my HEF

On very windy days my furnace shuts down. The code tells me either pressure switch (Checked myself and doesn't seem to be the cause) IDM (clean and running well) or a flue downdraft problem. I am a technician and I checked all of the pressure switch tubes for blockage and the motor seems to be ok too. My flu vents to the roof. There is a cap on the exhaust flu, but the cap has a hole on the top and all the cap does is reduce the size from 2" to maybe 1 1/2 ", Shouldn't the cap be solid on top to prevent downdrafts from happening? This only happens on very windy days. Any help would be appreciated

Empire_2

I assume hi Eff right?

Would help if we had a pic of flue termination. Also, flue should not reduced and should not have a hole in the middle. How many elbows, 45's and total length of pvc pipe, size of furnace, brand and anything else you can give us would help us answer your Q:

Darin(in Michigan)

High Efficiency

The only way to truly troubleshoot a pressure switch is with a magnahelic or a U tube manometer. You should know the make and break pressures of the switch as well. Carrier has a sheet with all the pressures of their PSs for each residential model they sell. If you have a BDP derivative I could give those to you if you know your model. If you plan to be in the field for a long time, you should get a tool for checking the switch pressure.

Glenn Harrison_2

Actually...

Lennox was infamous for specifying the exhaust be reduced one size at the termination (3" to 2" of 2" to 1 1/2").