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Thread: Furnace Question

  1. #1
    Plumber Cass's Avatar
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    Default Furnace Question

    Can anyone tell me the equivelent length of a 3" PVC short and long 90 on a 90% furnace exaust vent.

    I am being asked to lengthen the pipe by 7' and add 1 / 90 on the exterior of the house because it is dumping out next to a new hot tub.

    The max length of the run can be 70'.

    There is 31' of pipe 2 / 90s and 1 / 45 right now.

    Thanks

  2. #2
    Plumber/Gasfitter dubldare's Avatar
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    As far as I know, there is no generic standard for venting of 90+ furnaces. There are limitations on where intakes and vents terminate which are prescribed by code, and are standard. The actual sizing of vents and the equivalent losses for fittings varies by the manufacturer. When dealing with venting of these appliances, nearly all codes digress to 'installed per manufacturers specifications'.

    Hope the customer has the literature/installation manual for the furnace.

    That being said, I do know that you will not find an equivalent for a short sweep 90. I've yet to see or hear of a manufacturer allowing them.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    Depends on the specific restrictions on that particular brand. Just looked at a Weil-Mclain vent install manual...max of 2 elbows allowed. On the particular one I looked at (Ultra-80), the max length of straight pipe was 100', so that shouldn't be a problem with the added length (again, though it is up to the specific unit you have). They specify long-radius elbows to keep the back pressure down.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Plumber Cass's Avatar
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    Trane XL 90 Mod.# TVC120c96 o or 0 B6
    Last edited by Cass; 01-05-2006 at 06:47 PM.

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