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Thread: Indirect domestic HW from heating boiler

  1. #1
    DIY Junior Member John in herndon's Avatar
    Join Date
    May 2007

    Default Indirect domestic HW from heating boiler

    My cousin is installing a new boiler (high efficiency) in his house and will need to change out his old HW tank heater at the same time. The fuel is natural gas.

    I suggested that he use an indirect heater (such an an Amtrol) for the domestic HW. Any downside to this approach? The boiler location is being moved to another location in the basement and the new unit will be PVC vented. Since another tank HW heater would need a flue, I suggested the indirect tank.

    Things to avoid? Brand names?

  2. #2
    DIY Member msgale's Avatar
    Join Date
    Sep 2006


    indirect is best for efficiency, long life, no need for flue.
    overall, your best water heater option by far

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


    Don't oversize either the boiler or the tank, but if need to upsize one, make it the indirect. If the boiler is already a given, and it's 100KBTU+, even a 28-30gallon indirect will have more capacity than a 50 gallon standalone if run as a "priority zone". If the boiler is smallest-of-the-line 50-60KBTU, you may have to add some capacity to the tank to be able to pull back-to-back long showers. You only need truly large indirects if you have small boiler and big spa to fill, and want to do so in a reasonable amount of time. (At even 100KBTU of burner it can take awhile to fill an 80 gallon spa.) I've seen many a 50gallon+ indirect in houses where they had no business being, given the sizes of the boilers & hot water demands of the houses, just adding to the expense for no good reason.

    Efficiency-wise and longevity wise an indirect on a high-efficiency boiler beats all other options during the heating season, and beats standalone tanks during the summer season. Most will go several decades with little or no maintenance.

  4. #4
    Previous member
    Join Date
    Jul 2009
    North of the Mason dixon Line


    If you do the indirect thing (and you should) look into installing an outside temperature, boiler re-set control also. It will save you tons of money.

  5. #5
    DIY Junior Member juror58's Avatar
    Join Date
    Jan 2010
    Central NY State


    I have had an indirect hw heater for 20 years. It is a 40 gal SuperStore connected to a 96k Peerless HW gas boiler. I generally like it but...

    For the first 10 yrs of the installation there was just me in the house, and only 2 of us since then. Especially in the summer there are extended times when there is no draw on the tank, and therefore the boiler cools to ambient. If I come home from work and take a shower I often find the tank has cooled down (but not enough to trigger the aquastat) and the water turns cold after a short time under the shower. Since the boiler water is at ambient it has to warm up before it can warm up the domestic water, and the shower is finished quickly.

    If the boiler is warm (as it is apt to be in the winter) it can keep up with the draw with no problem.

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