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  1. #1
    Join Date
    Mar 2007
    Posts
    23

    Lennox G71 Furnace problems with stand by geneators

    I installed a gardian generator 10KW three years ago, my costomer forgot i sold furnaces a local competitor installed a G71 in Dec. They had a power outage last week everything worked but the furnace. I was there last week the generatoer would provide 119-120 volt 58.9HZ the furnace would not reset utility power comes on 122v 59-60 HZ furnace runs. The transformers
    secondary with the generator 27.6 volts thought it was a little high with the utility we had 28.7volts. Has any one heard if Lennox G71 are having problems with generators

  2. #2
    Join Date
    Apr 2002
    Location
    Omaha, NE
    Posts
    1,561
    Quote Originally Posted by dex1 View Post
    I installed a gardian generator 10KW three years ago, my costomer forgot i sold furnaces a local competitor installed a G71 in Dec. They had a power outage last week everything worked but the furnace. I was there last week the generatoer would provide 119-120 volt 58.9HZ the furnace would not reset utility power comes on 122v 59-60 HZ furnace runs. The transformers
    secondary with the generator 27.6 volts thought it was a little high with the utility we had 28.7volts. Has any one heard if Lennox G71 are having problems with generators
    It's possible the generator puts out a sine wave with too much Total Harmonic Distortion (THD) and the furnace locks out. See link:

    http://support.fluke.com/find-sales/...12_ENG_A_W.PDF
    B.O. = B.S.

  3. #3
    Join Date
    Feb 2007
    Posts
    999
    Great article, although I have to admit, I did some skimming.

    Years ago, I worked for a pharmacy chain that had NG backup generators in all of their stores. Some of the stores near the shore would have violent thunderstorms and would frequently loose power. At other times, and in other areas, power would be lost, randomly.

    When power was lost, those babies would start right up and the computer equipment wouldn't miss a beat. Only downside was the noise, as they were located in the back room.

    As far as I recall, they were 100% reliable, as they were automatically started weekly for 10 minutes, and the crankcase oil was changed routinely..

    In retrospect, I can't recall either freezing or sweating during the outages, so I guess the HVAC was covered.

    Amp

  4. #4
    Join Date
    Jul 2009
    Posts
    247
    I work with my dad to install generac guardians now. Your frequency looks a tad bit on the low side. All of the ones i've put in have always been in the 59.8 to 60.2hz range. Not too familiar with the older ones yet (just started a few months ago), but the voltage and frequency should be adjustable.

  5. #5
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,741
    Lennox had a service note out last year regarding running units on backup generators.

    units had no problem handling power supply in the 57-63hz range, biggest problem was reversed polarity or poor ground.

    flame rectification systems in these units require a proper ground or they just won't work.

  6. #6
    Join Date
    Jan 2010
    Location
    over here
    Posts
    458
    This might be totally un related. I found a lennox this year that wouldnt run with a generator. The generator was taking up too much of the gas supply and the burners wouldnt ignite. When the generator ran it took nearly all the pressure away from the furnace.

  7. #7
    Join Date
    Jul 2009
    Posts
    247
    Quote Originally Posted by JJDH View Post
    This might be totally un related. I found a lennox this year that wouldnt run with a generator. The generator was taking up too much of the gas supply and the burners wouldnt ignite. When the generator ran it took nearly all the pressure away from the furnace.
    That, my friend, is the result of improperly sized gas piping and/or gas meter.

    I currently have a 17kw Generac guardian (220k BTU), a lennox G61 (70k BTU), a Rheem RGFD Mod (66k BTU), and gas hot water (35k BTU). All run just fine when the generator is running, and both furnaces are backed up by the gen.

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