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High winds cancel the system's call for heat.


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I have a Rheem Classic Series Super Quiet 80 gas furnace. The unit is not quite three years old and every winter I have the same problem. When the winds get up and start to gust over 30 mph, this causes the heater to cut off and/or lock out until the winds die down. Once the winds are steady, and die down the heater turns on and returns to normal.

The local technicians cannot identify any hardware malfunction. The owner’s manual lists several safety features. One of which is the pressure switch that monitors pressure conditions within the furnace vent system during the heating cycle. Further, it states that there are several reasons for the pressure switch not to close. Item number four - "Severe downdrafts cancelling the draft from the inducer fan."

The technician believes there could be a downdraft problem that may be causing the pressure switch to open. The technician replaced the pressure switch and installed a high wind flue cap. The condition is still the same. Do you have any thoughts?

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Hi,

Those look like they might be more than 3ft. above the roofline - aren't those puppies supposed to be supported by guy wires when they're more than 3ft. above the roof (maybe it's 4ft. - I can't recall off the top of my head.

I'm thinking some kind of mechanical anti-backdraft damper is needed on that guy. It slams shut when the wind gusts up, but seconds later when the gust drops off, it swings open and lets the exhaust out. If they don't make such a turkey, perhaps a power vent up in the attic that's interlocked to the furnace. Furnace comes on, the power vent comes on and prevents backdrafting. Furnace shuts down, power vent goes off; I know they make those 'cuz I've seen them before.

ONE TEAM - ONE FIGHT!!!

Mike

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HVAC isn't my strongest suit, but I'd have to wonder why this otherwise normal set-up would require anything non-normal like an extra power vent? Nixond already posted "The technician believes there could be a downdraft problem that may be causing the pressure switch to open. The technician replaced the pressure switch and installed a high wind flue cap.". I think it's quite logical to have suspected a overly sensitive pressure sensor. Evidently, that's been replaced and that does look like a Simpson high wind vent cap.

Next, I would suspect something about the shape of this roof and/or the neighboring structure/roof causing an unusual high pressure vortex in the region of the termination. It might need a taller, not shorter flue. That would be very difficult to diagnose unless you happened to have the tech there at the right time.

Nixond, it seems like your HVAC tech is actually a knowledgable guy. He tried the obvious. It didn't work, but I think you would get better advice on further options from him than what we can offer "off-the-cuff" from afar.

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A steep roof like that will cause winds to spill and downdraft sharply as they cross the ridge; it's one of the reason that pilots are taught not to fly too close to the downwind sides of the crests of mountains.

ONE TEAM - ONE FIGHT!!!

Mike

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First, I would like to thank everyone for their replies. Just FYI, the furnace was part of an original install for my new home. My home is nearing three years old now. I have had three contractors/technicians look at this unique problem, and they are all stumped as to the root cause. I will try to include some pictures of the furnace as time permits.

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Shorten the flue two feet and the problem will go away. Thats my guess from this limited info. Get back to us and tell us what the tech said. The only condition that changes (fluctuates) is the out side air , WIND. As posted above when the wind picks up and the location of the flue in relationship to the top of the roof create an effect that wind is throwing air down the flue. When the wind is less than the 30 mph gusts as you said, the terminal throw (sorta) is dissipated by other wind currents, it loses it's strength. So my guess is that the flue is cut in to close to the peak or the flue is too high..

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  • 2 weeks later...

The problem could be that high wind conditions may be actually causing a high draft condition rather than a down draft and closing the pressure switch before a call for heat is initiated. The ignition control box is doing what it's supposed to do. One option Trane gave us on one install was to install a double action barometric damper with spill switch. Contact Rheem/Ruud about this possibility.

If however it is downdrafting and preventing the pressure switch from closing I would use the Field Controls Star Kap. It is much better at keeping a draft than the photo of the one installed. http://www.fieldcontrols.com/starkap.php StarKap2004.jpg

Another option is to vent the furnace with a side wall venting system by Tjernlund or Field Controls or a chimney top venter.

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