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garage heater install

Bigsteve Member Posts: 5
Just installed a mr. heater 125,000 btu natural gas heater in my garage. per mfr. instructions I used stainless steel 4" class III venting. I used a one foot section off the furnace, a ninety degree, then three- 3 foot sections to outside. Vented horizontally through the wall and it ends with a tee that is screened. The tee is 18" from outside wall. I followed all directions, including the 1/4" slope per foot. Overall length is within mfr recommendations. 25 foot for longest run minus 10 foot for the ninety leaves 15 and i am only at about 9 feet. The pipe itself seems to get exceptionally hot. I have dealt with double walled on a wood stove before, but never this stuff. The double wall never got this hot.
Is this normal or am I missing something? If not what should I check? Thanks for any help and response.


  • newagedawn
    newagedawn Member Posts: 586
    is insulated?
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • Bigsteve
    Bigsteve Member Posts: 5
    The garage itself is insulated well, 2 by 6 construction with blown in cellulose. The vent piping is not enclosed, well except where it goes through the wall thimble...
  • clammy
    clammy Member Posts: 2,983
    edited April 2018
    I hope for your own safety that the boiler was installed on a raised non combustiable base being most areas codes require any heating appliance to have its burner at least 18 or 19 inch above floor level due to possible flamable vapor concontractes when installed in a garage . Unless the boiler is sealed combustion ,Usually most fan assisted direct vents flues are very hot being it is only single wall .Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • Bigsteve
    Bigsteve Member Posts: 5
    Of course, It is hung from ceiling with threaded rods and proper hangers. All flammables are now stored elsewhere. Meaning gas, kerosene and propane....All spray cans of stuff like wd40, qts of oil etc. are at least 30 feet away from furnace.
    "Usually most fan assisted direct vents flues are very hot being it is only single wall"---thank you, now I know....