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Thread: Replacing an Indirect Water Heater

  1. #1

    Default Replacing an Indirect Water Heater

    I have an Amtrol WH-7L indirect water heater connected to my boiler. The boiler seems to be working fine, but the water heater tank has been slowly leaking for a couple of weeks (it took me a while to find the leak since it was coming out the bottom of the tank). Recently the leak started increasing and I can now hear and see that it is coming out the bottom of the tank because it is rusted through.

    I'm assuming the tank is done and I need to replace it quickly before it gives out entirely. I am wondering if I need to make any changes to my system or if I can find a cheaper replacement than buying a new indirect water heater??

    I just bought this house in December and I haven't seen it run in the summer where it is supposed to save on the boiler. I have been told by a friend that that they have a boiler and a well insulated storage tank that does not heat the water but just keeps it hot. I am wondering if I could convert from an indirect heater to just a water storage?

    The other problem I have is that my house is a 3-family with 3 bathrooms and a total of 6 bedrooms and I currently have a 41 gallon tank. I will probably have to increase the size of my tank or find a more efficient system because in the morning we occasionally run out of hot water.

    Is an Amtrol indirect heater the best on the market for performance, initial cost and lifecycle savings? Any help would be greatly appreciated as we don't have time to comparison shop correctly and don't have the money to replace the whole boiler/heater system. Thanks

  2. #2
    In the Trades Bob NH's Avatar
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    I have a boiler with tankless coil for hot water. I was using so much oil in the summer to keep the boiler hot that it cost more than if I heated the water in the summer with electricity.

    I installed an electric water heater in series with the tankless coil.

    In the winter, the water passes through the tankless coil and into the water heater. The water heater is set below the temperature from the boiler, so it uses no electricity.

    In the summer, I shut off the boiler and the electric heater takes over automatically.

    You can buy an electric water heater for a lot less than an indirect heater. Unless you have a gas boiler with condensing unit, you will probably cost more for fuel to keep the boiler warm than it will cost to heat with electricity. Feed water is warmer in the summer if the source is surface water. It doesn't vary much if you are on a well.

    If you put in at least an 80 gallon heater, you can sometimes get a special rate from the electric utility if you allow them to control the heating hours.

    If you are using natural gas, you may want to use a gas heater, with or without power-vent. I don't have any experience with that, but others on this board may suggest something.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    The indirect tank relies on the boiler all year to heat water. They come in various sizes. For the number of people, yours might be too small. SuperStor makes some nice tanks. I had one installed earlier this year. The tank is stainless steel, so it should last a long time. You are looking for two specs: first hour available hot water, and the standby loss (i.e., how fast it cools off - how good the insulation is).

    One thing that can help your first hour available use is to make the WH a priority zone, if it isn't already. This means that when the tank is too cool and needs heat, it shuts all other heating zones off and directs all of the boiler's heat into the task of reheating the water. Once it is hot, it returns to "normal". depending on how well insulated the house is, and how cold it is outside, you may never notice this switch in priority. If you have an old drafty house, it could cool off while it is heating the water while everyone is taking showers/baths.

    The alternative is to replace it and install a conventional WH. These do NOT have the capacity or recovery rate of a typical indirect, so you would need a much larger tank.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Like an engineer alternety's Avatar
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    A few things will help in your decision process.

    Is the boiler a modern condensing gas unit with a very low amount of water in the boiler (a gallon or two).

    A modern condensing boiler (almost all gas) can get up to 98% (or a teeny bit more if you believe some ads). That is better than you can get from any other fuel consuming heat source. An indirect tank is a good solution for this situation.

    If the boiler is not one of these you might consider upgrading the boiler at the same time. Look at up-front cost vs fuel savings. Depending on what you have it could be 20-30% or more less efficient that a modulating condensing boiler.

    Boilers can provide much more heat/minute than hot water heaters (electric is the worst, and you have to have adequete power and wiring available). Rate of heat generation equates to recovery time for hot water. If configured properly you can have "unlimited" hot water with an indirect tank.

    That is what I built. Modcon (modulating/condensing) boiler and stainless steel indirect tank.

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