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90 plus furnace in unconditioned space.

Hi all, for a nice rebate in NJ I need to install a 90% plus furnace, does anyone have a good way to install one in a unconditioned attic? with out having the p-trap freeze?

Are there any other concerns with installing a condensing furnace in a unconditioned space?

Comments

  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    Not being as efficient and duct losses.
  • NJ, Designer
    NJ, Designer Member Posts: 53
    I would never put a furnace in a unconditioned space if I had another option, My question is how do I make sure I won't have any call backs,
  • Tinman
    Tinman Member Posts: 2,808
    Yes, it's a condensing furnace in an unconditioned space! It's not only the trap you need to be concerned with but the secondary heat exchanger also. If there's a prolonged "no heat" situation with a partially clogged drain, the condensate could freeze and crack the secondary heat exchanger. I've seen it happen.

    In order to install a condensing furnace in an unconditioned space in my area, you have to enclose it in a small insulated room and have a secondary heat source provide heat to it. And that makes perfect sense to me. For many attic installations, that's not as big a deal as it sounds. 2x4's, 3/4" plywood, batts of R13, and some drywall don't cost all that much.
    Steve Minnich
    icesailor
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    And what's the secondary heat source?
  • Tinman
    Tinman Member Posts: 2,808
    On the new construction jobs I've been on in that situation, there was always at least one other furnace in the house, usually the basement. We'd run one 6" round/oval duct up to a sidewall register in the new furnace room. It's the only way we'd pass inspection.
    Steve Minnich
  • Tinman
    Tinman Member Posts: 2,808
    It was either that or they'd have to give us a small mechanical room on the second floor or put all the equipment in the basement.
    Steve Minnich
  • clammy
    clammy Member Posts: 3,103
    steve hit the nail on the head .Ive seen it done by one of my hvac buddies in his own home he put a small electric fan coil to keep it way above freezing and tthe heck out every thing .That heat lose from the duct work is a big one for me even with r 10 wrap properly done and not compressed w all joints sealed and r 10 flex w your cieling cans insulated and lets not forget the return duct work .For myself i hate it but there is certainly alot of it happening around my area espically with the add a levels its competive plus toss acoil n condenser and u got ac what general contractor wouldn t be happier and i must admit i ve tossed many in in my past life where my name was not attached to the shingle that hung on the building and they where 80 not 90 s but have seen it done and seen the damages .Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • NJ, Designer
    NJ, Designer Member Posts: 53
    Stephen Minnich, thanks for your input,

    Does heated pipe tape, work?
  • Furnacelady
    Furnacelady Member Posts: 29
    edited February 2015
    We do it all the time. We must use pans, insulated ductwork and we put a supply vent in the area. We add freeze tape to the trap. If you are going horizontal and have A/C make sure your pvc drain from the evap coil uses a separate trap than the furnace or else the AC trap will evaporate and blow air into the furnace trap which is open on top, to the air, to pervent a vacuum from sucking out the trap water. You will get water blowing all over the place or you won't get the proper vacuum to operate the pressure switches and the furnace won't come on. We tell the customer to never go lower than 55 degrees, just like the instructions read. I am in lower Michigan and have one in my garage attic. It's now 2 degrees out. I have 3000 sft, 3 furnaces 1st, 2nd flr and 80K in garage. Gas bill runs $300 in the coldest months. Carrier 98% Modulating.
  • Tinman
    Tinman Member Posts: 2,808
    @NJ Designer - the pipe heating cable will work well on the trap and the drain pipe but it won't protect the secondary heat exchanger in a no heat situation.
    Steve Minnich
  • Abracadabra
    Abracadabra Member Posts: 1,948
    Is there pipe heating cable you can use on PVC? I must admit I'm not too up to date on pipe heating cables, but many I've seen specifically state not to use on PVC..
  • unclejohn
    unclejohn Member Posts: 1,833
    The heat tape will work until it fails. I have had so many frozen discharge drain lines from the pump I can't count them this year. And on all but one there was a laundry tub 20' away. I would never put a condensing furnace in a attic.