Furnance help

[djcoop52]

Here is the problem with the high winds yesterday furnace would not stay running to much air is coming back down the outside exhaust vent and fan can't overcome it and shuts down. The back story I built house in 1993 old furnace installed at that time had an exhaust vent that went straight out thru rim board with a 90 degree elbow facing straight down ran that way for 20 years no issues. New furnace installed in 2013 used the existing outside exhaust no problems until Feb of 2018 when one really cold very windy day furnace would not stay running furnace has 10 year warranty had vendor out everything checked out only problem they could come up with was so much air coming back down exhaust when the furnace went from 1st stage to second stage fan could not compete with the air flow. Tech put furnace in one stage mode and ran without issue. Couple days later they came up with a fix for the vent turned it up a couple of feet then two 90s turned back down and put furnace back in 2 stage mode no issues rest of winter and no problems this year, until last night single digit temps 25 mph winds with gusts to 30 and same issue. Called installer, sent tech out different tech than in the past I explained past issue he checked out the furnace everything good we tried removing the 2 90s on exhaust, ran for awhile and again stopped he put furnace in one stage mode and has been running since. First stage, fan pulls 6 amps when it goes to second stage pulls 3 amps which is what it is supposed to do. I live in open farm country exhaust goes out west side of house and I live on top of a hill. They are going to come back out first of week and maybe have a solution. Anybody know how to get an exhaust vent that will not let extreme winds have this kind of effect on the furnace

[yarcraft91]

Did the techs consider running the exhaust pipe horizontally and capping the end with a tee, with the open ends facing straight up and straight down?

Our high-efficiency furnace exhausts through the roof, pointing straight up. Not a single problem with it in 30+ years.

[Hot Runr Guy]

Is the pipe diameter larger than it needs to be? maybe put a reducing fitting over the end?

HRG

[djcoop52]

Never thought about that concept but in my mind sound like it might work will mention it to them when they come back next week. Maybe would help or maybe would double surface area for wind to catch Im no engineer (no dummy either) people above my pay grade figure these things out. Was hoping maybe somebody else has encountered this issue. Any and all ideas are welcomed.

[djcoop52]

3 inch pipe. What I cant wrap my mind around is that it worked for years without this happening we have had many very windy winter days with no issues I keep questioning if the fan is weak and they keep telling me no that it is running as designed. The times it has happened wind is out of the west south west. Not the first time that has happened either that is the direction we normally have our winds from.

[Potatoe]

Try a wind block some 3/4 inch plywood mounted on some 2 x 4 with some weight so it does not take off.


Test the scenario with a good carpet fan, blow it right at the elbow with and without the wind block. Try to simulate the condition you are having.

[yarcraft91]

FWIW, I had a new 80% Ruud furnace installed in our cottage and had a problem similar to the one you describe. Turned out to be a bad pressure switch, the one sensing pressure in the exhaust stack. I found reports on the internet of the same problem in Ruud furnaces.

[kzoofisher]

May also have a drainage problem. At cold temperature the first stage can run for a long time and never satisfy the stat but never cool off enough to bring in second stage. Condensate builds up, air switch trips and you’re in alarm. Can the furnace be set to go to second stage after 10 minutes of run time?

Check the pitch of the exhaust pipe. Pressure switches are very sensitive. A little droop could cause it. Increase the pitch slightly and add the vertical tee.

[NailsWI]

Originally Posted by yarcraft91

FWIW, I had a new 80% Ruud furnace installed in our cottage and had a problem similar to the one you describe. Turned out to be a bad pressure switch, the one sensing pressure in the exhaust stack. I found reports on the internet of the same problem in Ruud furnaces.

I've gotta agree with the pressure switch being the likely culprit. If the furnace has run trouble free since 2013 until just recently I doubt that it's a venting issue. Tech should definitely change the switch out as it is relatively inexpensive and easy to change.