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Thread: Properly venting a Wei-McLain CGi-4E boiler into a flue?

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  1. #1

    Default Properly venting a Wei-McLain CGi-4E boiler into a flue?

    I had licensed plumbers install a Wei-McLain CGi-4E a few weeks ago. The venting problem was it goes into a flue along with a standard 50gal water heater. With my old boiler (an HE3), the 3" went into a 4" manifold that received the WH in a wye, and this worked fine. This new boiler is more powerful and they used just a Tee to connect the WH, now the boiler exhaust is coming out the WH hood.

    I've contacted them about this, but since they're obviously challenged by this, I'd like to hear some ideas about how it really should be done, short of the obvious solution of cutting a separate hole into the brick flue for the WH. There so much piping right there that's a big hassle.


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    Any pictures? What do you have to work with?

  3. #3


    Quote Originally Posted by dcelite View Post
    Any pictures? What do you have to work with?
    Hope these clarify. This goes into a 15' cinderblock flue on the blank side of my brownstone type building. I know it's not to code, but it's the way we bought it 12 years ago and apparently is grandfathered in. Street grade is a couple of inches above the bottom of the joists. My confidence is not too high in these guys, I watched the journeyman who actually installed the boiler bleed the crap out of expansion tank, and when I asked why, he said it was to get the air out of the system!! The other thing I'm not sure is right is how the vent rises straight out of the fan, so the condensation between there and the drip tee he installed drips back into the fan. The old boiler ran horizontal into a tee so condensation ended up in the dead end of the tee.

  4. #4
    DIY Member export!'s Avatar
    Join Date
    Oct 2009
    Ontario, Canada


    I don't know enough to call it right or wrong but I do know that I would want a CO detector in the area until I sorted it out. If you don't have one install one today.
    (I Am Not A Licensed Plumber)

  5. #5
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    You can't vent an atmospheric-drafted appliance into the same flue as a forced-draft unit like a CGi-4E without exactly this problem! You might have thought you were getting away with it with the HE3, but in all likelihood the same issue was present, just less obvious. Unless you're tapping into a separate flue, banging a separate hole for the WH solves nothing- just moves the Tee from the metal vent to the masonry.

    And at the 85% AFUE efficiency of the 4E a condensation tolerant flue liner or side-venting (not using the flue) might be necessary, if it's not already lined. (83% combustion efficiency is about the limit before flue condensation becomes a real issue.) If you side vent it you'd then be stuck with an "orphaned hot water heater" problem (google it.) But if it's lined with clay liner only (or unline) you may be in for extensive chimney repair in short years.

    Whether the CGi is side-vented or vented into a properly lined flue, the "right" solution to the venting of the hot water tank is probably to de-commission the tank and install an indirect-fired HW heater run as a separate zone off the CGi when all is said & done. It won't be cheap, but it should last forever in low water-hardness areas with minimal maintenance, and improve your overall AFUE.

  6. #6
    Previous member
    Join Date
    Jul 2009
    North of the Mason dixon Line


    Besides Dana's timely comments, You are NEVER grandfathered for installing gas appliances into an unlined flue. Whoever installed that abortion should be hauled before a judge. I can't believe you paid them for that mess. There is so much wrong there I can't even begin to list it all without getting a headache. Call your lawyer!


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