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Proper way to vent a condensing forced air furnace?

Lou S.Lou S. Member Posts: 5
I'm looking to buy a new.."used" home built around 1993. After checking the mechanicals out, I found the 80 plus furnace vented a different way than I seen on some other homes that I've visited in the past. First, the intake seems right,coming in from outside on the horizontal,and feeding the furnace, but the exhaust goes straight up and through the roof. Is this the right way to do this? It has a tee at the furnace to catch the condensate and a small barb with a hose to drain away the collected liquid.Plus there's no "jap cap" at the roof..just an open 2"pipe. Doesn't this need to be two street ells making a loop and looking downward to keep out the rain?
After calling my furnace tech buddy, he suggested to eliminate the fresh air intake and let it injest the room air, then use the old abandoned air intake and use it as an exhaust? Good or bad idea? Your input is appreciated..By the way, the furnace is a Temp Star brand, which I've never heard of..AND..It's piped to the roof with schedule 40 PVC..


  • TonyTony Member Posts: 608
    what type of pipe

    is the vent ? To go horizontal you'll need SS. Eliminating the combustion air intake will increase the infiltration of your house, increasing the heatloss. If it's SS through the roof I'd leave it be. If it's Plex-vent or Ultra-vent (plastic, but NOT sch. 40) it's gotta go ASAP.
  • Steve MillerSteve Miller Member Posts: 115
    proper way to vent

    The proper way to vent it is to find the owner's manual and do it they way they want. Every manufacturer is different and here in El Paso County in Colorado, the manufacturer instructions trump the UMC.

  • Paul MitchellPaul Mitchell Member Posts: 266
    90plus is what it is actually

    Most of the time we try to terminate where we intake. But if system has been operating fine then ok. I would NEVER get rid of the intake....Why? Using outside air is much better. Best deal is to find a Tempstar dealer in our area to check things out.

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  • DaleDale Member Posts: 1,317
    Roof venting

    First, the only way to vent anything except a catagory 1 is by manufacturers instructions. If you look at the name plate you'll see catagory 4 I hope. If it isn't 4 the pvc is a hazard. It is perfectly acceptable and IMHO much better to vent straight up through the roof just the way you describe it, if a tiny amt of water gets in so what, it is designed to drain back to the furnace. What may not be OK is the intake in a different pressure zone that the exhaust, you'll have to look at the install instructions, manufacturers usually like them in the same pressure zone. The modern roof system is concentric vent pvc.
  • Mike BMike B Member Posts: 155
    Tempstar is a division

    of ICP. FYI. Get the manual. Most 80% furnaces are not sealed combustion. Most likely a fresh air intake due to limited combustion air supply. Vent at roof if it is a 90%+ condensing is not a problem as the unit would be connected to a drain. Plastic on an 80% is a big NO-NO. The information you give is conflicting. High temp plastic for 80+ is 3" usually.
    Good luck.

  • AdamAdam Member Posts: 400

    ICP stands for International Comfort Products (, in order to get hold of the manual or help, you have to call one of their authorized distributors and ask to speak to the TSA (Technical Service Advisor), they are trained on all equipment and can help you. The factory won't speak with you! I just installed a 90+ scorched air system in a vacation home so the client wouldn't have to worry about freezing up a hydronic system. We put in a Heil (made by ICP) and it's really very nicely designed and well built. I was impressed. Good luck!
  • JonJon Member Posts: 109

    I installed a 90+ (not an 80+)furnace in my in-laws venting it that way. But a 80+ furnace does not allow the use of pvc for venting...........
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