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Weil HE common venting....

kcoppkcopp Member Posts: 3,497
I did a service call on a 27 +/- yr old Weil Mclain HE-4 Nat gas boiler. Power vented. It was vented in 3" galvy sheetmetal into a 5" B-vent chimney. Also vented into the B vent was a 40 gallon std. atmospheric water heater. Boiler is in good shape. What bothered me is that I didn't think you could put a power vented unit into a common chimney w/ a std vent appliance. I looked at the brochure from 30 years ago and it says that this is acceptable... that is news to me...Or so I thought. Your thoughts? I am probably going to suggest a new indirect water heater.


  • icesailoricesailor Member Posts: 7,265
    I never thought it was OK then, I know it is not acceptable now.

    If it was a VHE, that galvanized smoke pipe would be rusted cheese by now.
  • Tim McElwainTim McElwain Member Posts: 4,362
    NFPA 54 allows natural draft appliances to be vented into the same flue as fan assisted. The key word is "fan assisted" not power vented. The difference is fan assisted has a negative pressure at the breach, power vented is positive pressure and must be isolated and sealed. It is the incorrect use of terms as folks call everything with a blower power vented that is not so. The blower on fan assisted equipment is to overcome the internal resistance of the boiler or furnace and will have negative pressure in the vent just like any atmospheric equipment. The other thing you will notice with fan assisted is the burners get their air for combustion from within the room in which the equipment is installed.

    We also some times confuse sidewall vented equipment by using wrong terms, all side wall vented equipment is not mechanical exhausting (different rules) some is direct vented (another set of rules).
  • kcoppkcopp Member Posts: 3,497
    I don't think this is a "fan Assist".... as in a Power gas burner.
    How does the term induced draft figure in?
    Please help me differentiate.
    I did get the strong gas odor as I opened the basement door.
    Makes me wonder if the WH is venting into the basement when the boiler is firing.

    Here is the manual....
  • Tim McElwainTim McElwain Member Posts: 4,362
    The term fan assisted is the same as induced draft. They are not however classified as Power Burners. The HE along with some other boilers from Weil McLain that came along later (CGA, CGS) could be installed into a chimney by increasing the flue connector size or they could be sidewall vented using a smaller vent (see the HE installation manual you attached) On page nine (9) under chimney draft venting gives the following in the second paragraph To vent with another appliance, see National Fuel Gas Code, ANSI Z223.1 Appendix G for sizing.

    Is this vented into a lined chimney if so it an be connected with another appliance
  • Tim McElwainTim McElwain Member Posts: 4,362
    As for the odor of gas make sure there are no leaks in the piping as I am sure you know. Then fire all the equipment together and test with a combustion analyzer to make sure you are getting a stable draft with all equipment operating. The code allows them to be flued together but that does not mean that it will always work correctly. Fan Assisted with natural draft using the same common vent connector the connection should be made with a "wye" connection not a regular tee. If the appliances are separate into the common "B" vent then it should be the smaller (water Heater) above the larger.

    The connector by the way from the HE going into the vertical "B" vent should be 5".
  • Tim McElwainTim McElwain Member Posts: 4,362
    Make sure the flap inside the Transition Assembly/Blower Cabinet is not sticking as that will cause delayed ignition and could be the cause of gas odor.
  • kcoppkcopp Member Posts: 3,497
    When I said power burner I was thinking conversion burner...Carlin EZ gas or a Midco economite.
    I guess the odd thing is why install a HE into a B vent instead of a nat draft unit?
    Thanks for the explanation and the tips.
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