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oversized heater

ray hickethier
ray hickethier Member Posts: 26
I have a friend that had a condensing gas furnace installed last year and then the guy went out of business. He keeps getting a high limit code blinking. The temp rise is 75-80 degrees. The btu value is 78,000 output for a small 1st floor home. He has a separate furnace for the 2nd floor. My question is can one of the 4 burners be eliminated to lower the btu's rather than replacing the oversized furnace? If not, why not?


  • clammy
    clammy Member Posts: 3,113
    Thats really a no no there s alot alot of issue one of which is the manafactures usually never condone the removal of a burner .You may be able to change the orifices in the gas mainifold or low the manifold pressure but this should be left to a professinal with a combustion anyzler.Have you made sure the return filter is clean and the blower itself is clean ,also chk that all and return registers are open .Have you done a heat lose to confine that the unit is over sized .Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • Ironman
    Ironman Member Posts: 7,379
    It's illegal to do it and voids the certification of the furnace.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • unclejohn
    unclejohn Member Posts: 1,833
    Is there a A/C coil above the furnace. Make sure it's clean and does not block the outlet of the furnace. Some older coils have a very small inlet area.
    JUGHNE Member Posts: 11,077
    It is probably not so much that the unit is oversized for the house, most probably are. The issue is more likely that the ductwork is undersized for the heating unit.
    Been there and have the T-shirt. Customer/Owner insisted on up sizing from an 80 to a 100,000 because he had a leaky house. The billing indicates that upsize requested. The unit went for 15 years until I added a by-pass humidifier and suggested pleated filters. Between the two, the added air flow restriction of filters and the hot air by passing into the return caused the hi limit to trip and eventually not auto reset. The filters were the main culprit and going back to standard filters kept the temp rise down enough to avoid high limit.
    And this is with the blower set on high speed for heating. Also the burner NG pressure was set down to the minimum for just a little less fire, may have helped a little.

    Your friend could try a higher blower speed if that has not been done already. It will get rid of the heat quicker, heat the house quicker and continue to short cycle as it probably does anyway. But off on hi limit is not good, overheats heat exchangers and will wear out the limit switch eventually. Also causes excessive use of start components...ignition module and HSI or sparker.