Heating, Air Conditioning, Fridge, HVAC/Frozen furnace vent


Hello Craig,
My high efficiency gas furnace was installed in 2010. I have no air conditioning unit. The furnace vent clogged with ice from the outside in the dead of winter in 2014.
I was gone about a month so my house froze and flooded. I was told by the HVAC installer it happened because I set my thermostat under 60 degrees when I left. I always lower my temp to 50 or 55 degrees when gone for a long period. I have seen ice form on the pipe when my temp is set above 60 so I do not think that is the reason.
Intake and exhaust vent into one pipe and I have what is called a "mushroom cap" on the outside wall.
Please advise. I want to fix the problem.

I live in the South, so freezing weather and pipes is not big here, though it does get cold enough a few days a year to make ice outside.

I have hard time believing the indoor set point is the problem.  Although the lower the set point the shorter the unit runs creating less heat and might not melt all of the ice.  It seems to me there is an issue with the way the vent line was installed and the installer is not wanting to take any blame for the issue or they are just clueless and should not be installing HE furnaces.  The manufacture has specific installation instructions to prevent the ice from forming.  I would contact other service companies for a second or third opinion.  You might reach out to the manufacture to see if there are any other installers in the area.  If you find it was installed improperly, then get it fixed.  At that point you might have a case against the installer and can contact the local or state licensing board or take them to court.


Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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