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What size hole needed for two water heaters?

noobbathroom
noobbathroom Member Posts: 6
edited June 2021 in Domestic Hot Water
We currently have a 50 gallon AO smith water heater venting directly into the chimney through a 7 inch square hole in the masonry but a 4 inch hole in the chimney.

We are wanting to update to two 98 gallon AO BT-100 water heaters which combined would use a max of 150k BTU. We're having a hard time get the info we need on whether we can do it. The chimney is 7'x7'20. The hole would be about 8ft high going into the masonry and then the chimney. It would be underneath the beam which we are told by the mason shouldn't be a big problem.

Here's the installation manual fro the BT-100:

http://productcatalog.sheret.com:8080/DocServer/DSAnonDownloadServlet?action=download&type=product-artifacts&key=DS069ff973-f277-4b0d-bc61-88962bfe2127

Here are photos of the area we are dealing with and what the previous hole looked like. The new hole would go under neath the bricks. Thanks for your help!!











Comments

  • Steamhead
    Steamhead Member Posts: 17,387
    Are there any other units exhausting into that chimney?
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  • noobbathroom
    noobbathroom Member Posts: 6
    Steamhead said:

    Are there any other units exhausting into that chimney?

    Nothing else vents out the chimney, although there is a fireplace so I guess that does vent out the chimney.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Fireplace can’t be in that flue.
    I’d wait for @Bob Harper but I think you should line the chimney with a properly sized smooth wall liner, stainless steel wye into the room, reduced to proper sized flue pipe to each appliance. I’d also would like to ditch the draft hoods and use double acting baros with spill switches

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  • noobbathroom
    noobbathroom Member Posts: 6
    STEVEusaPA said:

    Fireplace can’t be in that flue.
    I’d wait for @Bob Harper but I think you should line the chimney with a properly sized smooth wall liner, stainless steel wye into the room, reduced to proper sized flue pipe to each appliance. I’d also would like to ditch the draft hoods and use double acting baros with spill switches

    I'm thinking there are two flues. Maybe the fireplace goes into it's own flue.
  • Bob Harper
    Bob Harper Member Posts: 1,091
    Looks like a nominal 8x8 for the heater flue and a 13x13 for the fpl. I'd go with a 5" smoothwall or 5.5" corrugated. You can use a ss tee at the base to make that turn but since it's CMU block I'd bust out enough to make a broad radius sweep at the base with a ss wye cemented into the wall with the breach at the top. This renders the leg as a condensate trap/ inspection/ sweep port. The cap can act as a trash can. You shouldn't have much condensate with draft hoods and I agree on the baros instead. One thing you need to do is pack the cells of those CMU blocks with rockwool or cement. They'll act as chimneys and channel heat right up to that combustible mudsill and pyrolyze it.
    You want the shortest water heaters you can get so you'll gain the maximum vent rise. Make sure the water heaters are as close to the chimney as possible. The code limits it based upon the vent connector size. You can manifold the vent connectors before entering the liner. Just size the common vent connector. Use a 'wye' fitting instead of a tee where possible. Actually, they're a 'Siamese' but the industry uses the term wye. A Siamese merges two into one whereas a wye splits one into two. We're bass-ackwards.
    HTH
  • JUGHNE
    JUGHNE Member Posts: 11,279
    Bob, so you see no problem with bringing the flex out of the chimney as the "hockey stick" configuration?
    How about then using the tail of the flex to make the first 90 for the horizontal run?

    Or would a standard 90 ell be better?
  • Bob Harper
    Bob Harper Member Posts: 1,091
    You can do a "pull-through" broad radius ell into the room a few inches, which provides better flow. However, a tee is often easier to install and provides a cleanout/ condensate trap. I wouldn't use a 90 as the seams collect condensate. I use them below a 90 if I'm sweeping the cleanout into the room. I'll do the tee, then adjustable ell to about 45 degrees, possibly an extension, then a removable cap. This may terminate in the wall behind a cleanout door or I may sweep the cleanout into the room where it is accessible. On wood and oil, I try to incorporate a short section secured to the cap so all the crud stays in the cap like a trash can for disposal. However, where I'm concerned with condensate or soot removal and I have the room, my favorite is a custom made wye fitting so it's all one piece and both the exhaust through the upper branch and the cleanout/ inspection port just flow smoothly. HTH

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