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Proper flue sizing

olpalbud Member Posts: 3
I am looking to add an oil fired hot water heater to the same flue that my oil fired furnace is using (masonry chimney tile lined). I am looking for the formula you use to determine if the flue is adequate for such an installation. Thank You.


  • Al Letellier_21
    Al Letellier_21 Member Posts: 402
    combo flue

    Don't know where you are, but here in Maine, we can only due what you are planning if the chimney flue is large enough for the larger of the two units, and we have to install a priority controller to keep the two units from running at the same time. Also, adding a second unit will require lining the chimney if it isn't lined.

    It's done all the time and quite successfully. We use a Taco or equal relay with priority and give the domestic heater priority.
  • Big Ed_4
    Big Ed_4 Member Posts: 1,901
    edited September 2010
    Flue Sizing

    Google chimney sizing chart , sure a good one would pop up... Chimney size , hight , horozontal run and total btu input all makes a difference... most towns follow the federal standards but can supersead , call the town ....
    I have enough experience to know , that I dont know it all
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