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Thread: Indirect Hot Water Tank vs. Hot Water Storage Tank

  1. #1
    DIY Junior Member
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    Default Indirect Hot Water Tank vs. Hot Water Storage Tank

    I have an oil fueled boiler that supplies the hot water by coil (currently no stand alone hot water tank). It simply can not maintain constant temps or supply enough hot water. So I'm thinking of installing either an indirect hot water tank that abandons the boiler coil for the coil surrounding the new tank OR just a hot water storage tank that will be replenished by the existing boiler coil. Looking to get a feel for the pro's and con's for each to make a decision.

    Any comment or experience with one or the other would be helpful.

    Thanks.

  2. #2
    In the Trades Bob NH's Avatar
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    I had your setup and made the following change which has been very satisfactory.

    The boiler was using a lot of oil in the summer just to make up for heat that goes up the stack while the boiler stays hot for when hot water was required. It was costing more for the oil than it would have cost for the electricity.

    I installed a 40 gallon electric water heater that is fed by the tankless coil to the inlet of the water heater. I turn off the boiler in the summer and let the water heater take over. The electric heater is set at 130 F. When the boiler is operating, it supplies hot makeup water to the heater and the electric elements don't come on.

    The system stabilizes the temperature between winter high demand times such as when you are taking a shower.

    The system will work just as well with a gas water heater.

    I found that the saving of oil, which is now about $2.20/gallon, is about twice what it cost me for electricity to heat the water in the summer. In the winter when the feed water is cold (municipal water is from a lake), the water is heated by less expensive oil.
    Last edited by Bob NH; 01-25-2006 at 07:00 PM.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    Some of the newest condensing boilers are 94% or more efficient. Unless you use an electric HWH (essentially 100% efficient), electric is more efficient - then it comes down to the relative costs of the energy. A gas hwh may be in the 70% efficient range? (I haven't looked recently - you'd need to check). On an older boiler, it is hard to say which is more efficient, vs a standalone gas hwh. Most of the newest high efficiency boilers only have a few quarts of water in them, if that, so they have a quick heat up and low standby losses. So, you need to take into account your system's design and its age; no one answer will work out best for all.

    When I replace my system, I'm going to go with an indirect tank with a high efficiency condensing boiler (or at least that is the plan).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Junior Member
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    Thanks both for your thoughts / insights... much appreciated.

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