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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


    The advantage of an indirect hot water tank are:

    1) You only have to purchase/maintain a single burner
    2) The boiler is used 12 months a year, reducing the problems associated with an inactive boiler for 6 months
    3) As you noted, a single stack

    I use an Weil-McClain 40 gallon (36 DHW, 6 for boiler circulation) indirect. I have 3 full baths in my house, me, my wife and three teenagers. We have never (ever) run out of hot water, even while running the dishwasher and clothes washer.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Go with a higher efficiency unit, vent out the sidewall and an indirect and don't look back. Modern condensing boilers are designed for cold starts and an indirect is insulated as well as or better than your electric unit. If you pick something like a SuperStor Ultra, it should last for a very long time (mostly SS). You can generally get by with a smaller indirect than a stand-alone unit as the boiler is generally a larger heat source to recovery/maintenance to produce hot water is better. While an electric WH is close to 100% efficient, gas, per BTU is cheaper, and a good boiler can be in the 90% efficiency range. Plus, most utilities are giving rebates for efficient units, lowering your overall cost upfront, and forever.

    The biggest issue is to size the thing properly. It would be a rare occurance that you actually need the same size boiler as what is there. Oversizing means lower efficiency and shorter life. Get a good analysis done. You can determine your heating load fairly accurately by comparing your oil useage to the heating degree day history information adjusted to the efficiency of the boiler you have now. It is likely that the actual load is in the order of 1/3 of what you have. This saves money all the way around as longer cycles are much more efficient than short ones and cycles kills the equipment.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DoD Army bjferri's Avatar
    Join Date
    Jun 2007


    Absolutely correct - I guarentee you I won't look back. I like this set up!

    Last edited by bjferri; 09-12-2011 at 01:45 PM. Reason: forgot to say thank you :)

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