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Thread: New Tankless Water Heater

  1. #1
    DIY Junior Member tonyc37's Avatar
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    Mar 2013
    Lenexa, KS

    Default New Tankless Water Heater

    I need a new water heater and I am thinking about a tankless unit.What I want to know is can I vent it through the existing vent from my old water heater or do I have to run a new vent.

  2. #2
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Aug 2009


    Tank-less heaters need a 4" vent. Most tank type heaters are 3". Plus you may need a larger gas line. Tank-less are 3/4" and tank type are 1/2".


  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
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    A tankless water heater is much more efficient which means more moisture in the exhaust. You "can not" use the old chimney.

    You will need either a new plastic or a new stainless. Most are being done with plastic.
    The old galvanized steel won't cut it.
    Last edited by Terry; 03-03-2013 at 02:00 PM.

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