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I have a gmpn-80 janitrol 90% eff gas furnace,it is only 15 months old,my condisation tray is melting and cracked do to heat in which case leaks water all over....why would this be happening?

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  • ride017 Jun 28, 2008

    I had a tech from the company who istalled the unit check the gas pressure and fan speed,he said they checked out properly.My warranty ended three months ago so they are trying to avoid fixing it.....I say it was an improper install or manufacture default.In your opinion ,do you think a problem in the existing duct could cause this problem as far as air draw?thx for the help



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Most likely the cause is that the furnace is firing too hot. When a furnace is installed and set up, the manifold gas pressure and fan speed has to be set by the technician so that the temperature rise through the furnace is a maximum of 50 deg F (i.e. if air enters the furnace at 68 deg F it come out no hotter than 118). The target temperature rise on any gas furnace is anywhere between 30 and 50 deg F. If the furnace runs too hot, either the manifold gas pressure must be turned down or the fan speed must be turned up to keep in this range.

Posted on Jun 28, 2008

  • Chris Lyon
    Chris Lyon Jun 29, 2008

    That is a possability. The big key is to measure the temperature difference through the furnace. Take a temp reading at the return vent and then take a reading at the closest vent to the furnace. Turn the furnace on and allow it to run for about 10min before checking temps so that the heat exchangers and duct work can get completely up to temp. If you are in the 30-50 range, then you are looking at install problem, mfr defect, or improperly paired equipment. Gas pressure doesn't really mean much if you are over temp. Natural gas normally runs at 3.5" water column in the manifold. I have a propane furnace. Propane runs at 10.5"wc in the manifold, but I fire my furnace at 8.5" to achieve the proper temperature rise.



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