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Thread: Replaceing Oil Boiler and Electric Hot Water Heater w/ Gas

  1. #1
    DoD Army bjferri's Avatar
    Join Date
    Jun 2007

    Question Replaceing Oil Boiler and Electric Hot Water Heater w/ Gas

    I need help making this decision please…looking at it from a long term economical stand point.

    A) Do I purchase a hot water heater and boiler and vent through the chimney? If so, I’ll need to spend $2000 for a stainless steel liner to re-line the chimney.

    B) Or, do I spend a little more for high efficiency boiler and direct vent to outside and not use chimney?

    If I go with Option B, what do I do about the hot water heater? I was told I could use an indirect water heater with the boiler…is this a good idea?

    Thanks in advance… any ideas would be helpful.

  2. #2
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010


    Option B and the indirect.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  3. #3
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    What Tom said. By the time you factor in the cost of an SS flue liner it's cheaper to buy a condensing boiler.

    Depending on your actual heat load there's a middle-ground. Power drafted 85-88% AFUE cast iron boilers exist (some sealed-combustion, others not), and may be a suitable alternative. But the smallest of them are 2-plate units with ~40-45KBTU of output. If your heat load is well under 30KBTU at design condition you'll get much better peformance out of the smallest-in-class modulating-condensing boilers. And if you can't park the thing next to a wall you'll be into some fairly expensive stainless steel side-venting, if local code prevents you from using B-vent even as a chimney liner. (Some places will allow B-vent as a liner for gas boilers, but not for oil.)

    By the time it's said & done, with any federal/state/local subsidy for going with a mod-con it may be cheaper & better up front to go with the higher efficiency. Just be sure to buy the smallest unit that actually meets your design-day heat load- a 3-4x oversized mod-con will cost more up front and likely short-cycle itself into an early grave.

    Be sure to seal up the unused flue, otherwise it'll be driving air-infiltration 24/365. With a sealed-combustion mod-con you can make the place super-tight without fear of backdrafting issues, and doing so will lower your heating AND air conditioning bills.

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