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Thread: Electric Water Heater into Oil Fired Coil??

  1. #1
    DIY Junior Member capercanuck's Avatar
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    Default Electric Water Heater into Oil Fired Coil??

    Hi,
    I have a question which might be weird.

    I have some rental properties that have heating and domestic hot water supplied from oil hot water furnaces. Domestic hot water is through the coil of the furnace.

    One duplex is complaining of a lack of domestic hot water. My furnace guy has recommended either replacing the coil, or going with an indirect hot water heater (water tank heated by the coil).

    I'm not sure if it matters, but Kwh here is .$12347.

    I'm looking at the cost of the indirect, versus installing a 30 gallon electric hot water tank as a "pre-boost" to the existing coil.

    The electric option on the front side is much less expensive.

    Is it even possible to do this? I'm an electrical contractor and the material/labour costs will be minimal, but I'm wondering will this work?

    Thanks in advance!
    Last edited by capercanuck; 02-16-2011 at 12:31 PM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Most coils can provide only limited heat gains or relatively small volumes. Now, some commercial units could provide what you need, but you'd have to look at the specs. Also, if the coils haven't been demineralized, they may not be working at their optimum (depending on the system, it might need to be done annually).

    A small electric WH would run out of capacity relatively shortly (you only get maybe 80%, so 24-gallons on what you were considering), and then you'd be back to the same situation as it not being there at all until usage stopped, and the electric WH could catch up.

    An indirect is more reliable and, if sized properly, should be able to provide ample water as it would have the entire boiler to recover with (assuming you ran it as a priority zone - may not be necessary but would give the most output and fastest recovery). Depending on your gas costs, it typically is a lot less expensive to do an indirect verses a properly sized electric.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member capercanuck's Avatar
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    Hi jadnashau,

    Thanks for the reply.

    We have oil here, not gas. I wish we did have gas though.

    Oil prices are rising and that is one of the reasons I'm considering the electric option.

    One of the reasons I'd like to explore the electric with oil option is that I thought I would be able to shut the oil furnace down during summer months, and run strictly electric.

    Also, since I'm in the electrical field, I was thinking of installing a timer controlled relay for the hot water tank which would allow me to shut the electric tank down from 10pm till 7am (example).

    I've got tons of control gear kicking around that I'd like to use. I've got a 365 day timer that I could control the oil furnace with, in conjunction with an external thermostat for the exterior of the house. As an example, shut the oil furnace down from July 1 - September 1 on days the outdoor temperature is above 70 degrees.

    The apartments have a maximum of two people in each, with what I would consider a relatively low hot water consumption.

    Again, these are just thoughts I'm considering. I know I can do the control end of it and it will work, it's the plumbing/boiler theory that has me stumped.

    Thanks fort he input.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Put the electric tank after the coil, and install a bypass around the boiler for when you want to shut the boiler down. This way, the heated water will go into the tank and the tank will only need to maintain the heat, not generally heat it. For a duplex, you are going to need more than a 30-gallon tank, though! That would give about one 10-minute shower with nothing else going on, and then take a half-hour or more to reheat when the boiler wasn't running, not counting someone else running any hot water for anything else at the same time. Code probably defines a minimum size for this situation, but I don't have the references.

    Doing it this way, there'd be no timers needed, but you'd have to turn a couple of valves to bypass the boiler.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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