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power vented boiler into chimney with water heater,Icesailor thoughts?

jonny88 Member Posts: 1,139
Hi guys,I got a call.Fan on boiler is shot.I was under the impression that you could not vent a power vented boiler with an atmospheric draft water heater into a chimney.I called weil mc lein and got two different answers.I asked a heating consultant I know and he said absolutly not as you can back draft water heater.Thanks for your help.


  • JStar
    JStar Member Posts: 2,752
    edited September 2014
    What model boiler? If it's forced draft, then I would be concerned. If it's just induced draft, then there's no problem.

    You can power-vent BOTH appliances with a Tjerlund or Field Controls fan.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    Yes, the terminology "power vent" indicates a different animal than a typical draft induced boiler or furnasty. Which, like JStar said, can have an atomospheric WH venting in the common pipe to a chimney.
  • Bob Harper
    Bob Harper Member Posts: 922
    Venting for positive flue gas pressure must be listed as such. No chimney is listed for positive vent pressure (the UL STP is considering it). If you common vent using aftermarket devices, you really are supposed to get approval from your AHJ but regardless, those devices cannot be at the appliance where they generate positive flue gas pressure going into a chimney. Even if common vented with AL29-4C listed ss venting, to common vent under positive pressure means it can blow back out the unit at standby. Putting a fan right at the vent termination places the entire vent under negative pressure and thus would be the only acceptable configuration.
  • Tim McElwain
    Tim McElwain Member Posts: 4,515
    If the equipment in question is marked as a Category I venting appliance and the water heater is Category I then it is okay. The furnace or boiler in that case would be classified as Fan Assisted which means the pressure in the flue would be negative on both appliances. I would however make the connection for the two appliances with a wye rather than a straight tee. The purpose of the fan on the heating appliance (fan assisted) functions as an induced draft overcoming the internal resistance of the furnace heat exchanger or boiler sections as an example. These are not sealed combustion chamber appliances but typically are atmospheric equipment, getting their air for combustion from within the space in which they are located.

    If you go to the venting tables in NFPA 54 National Fuel Gas Code or the International Fuel Gas Code they are listed as "NAT"/"FAN" for sizing.