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Considerations in adding an indirect tank to a combi system

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jeanc
jeanc Member Posts: 18
I am looking for the most cost effective way to add a tank to my system. I was sold on a combi (triangle tube 125) and to go tankless. We eventually got used to the low GPM .But I'm about to sell my house and I feel I should address this issue so it doesn't come as a surprise as most homeowners like me don't understand these details. All you have to do is try to run two faucets at the same time to see the issue. The general consensus from posts here and a few plumbers I've spoken to is to add an indirect. For long term efficiency, I get it. Certainly 1 gas fired appliance is better than 2. But if you put efficiency aside and think about install costs(I know blasphemy but bear with me), how does an indirect compare to an electric tank or direct?

There are 2 main concerns/questions: 1) What is the impact of the indirect on the heating system? I'm thinking about a 30-40 gallon tank. Does it take a long time to heat the water? Right now, a 10 minute shower doesn't create a noticeable effect in the heating with the combi. But if it takes 1 hour to generate water for the tank, it could be a problem 2) Given I'm not going to be in the house long, is going with a direct or electric, a bad idea?

Jean

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  • hot_rod
    hot_rod Member Posts: 22,266
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    With an electric downstream of the Combi, you are still covering load with the gas fired appliance. I would guess a 40 gallon electric would be much less $$ than an indirect. If you plan on selling, that is the route I would take.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    kcopp
  • Paul48
    Paul48 Member Posts: 4,469
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    @hot rod

    How about a cheap 40 gal electric, not wired? icesailor use to talk about using the bottom t-stat to control a circ.
  • SWEI
    SWEI Member Posts: 7,356
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    Don't really need an indirect, since the combi already handles the separation. You can use the electric as a buffer tank by adding a small circ and using the tank thermostat to control it.
    njtommykcopp
  • jeanc
    jeanc Member Posts: 18
    edited April 2016
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    Thank you. Now a stupid question -- is an 'indirect' referring to a special appliance that has a tank and input coming from the boiler vs a 'buffer tank' which is simply a tank that keeps the water warm? Are the two generally vastly different in price for the tank and the labor more tedious with an indirect? Or the other way around. I'm not quite clear on what the indirect does that is special other than being less expensive than an electric tank.

    Came across this article which talks about supplementing a tankless heater with a small electric tank. http://www.chandlerdesignbuild.com/files/fhbDecJan08.pdf

    Curious if this is what the suggestions above are indicating. The tank is simply keeping a supply of hot water. It's accomplishing the same thing as the indirect but using less efficient electricity (rather than gas of the indirect) to keep the water warm. Is that correct?

    One other question - A plumber told me that to do the indirect, it would require removing the use of Outdoor reset since the boiler would need to run to 180 degrees. that sounded really odd to me. I may have misunderstood. Does the boiler need to run at 180 in an indirect configuration?

    Finally would it make any sense simply to get a electric hot water heater to keep it completely separate from the boiler?
  • SWEI
    SWEI Member Posts: 7,356
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    jeanc said:

    is an 'indirect' referring to a special appliance that has a tank and input coming from the boiler vs a 'buffer tank' which is simply a tank that keeps the water warm? Are the two generally vastly different in price for the tank and the labor more tedious with an indirect?

    An indirect water heater has a coil inside (in place of a burner or heating element that) carries boiler water to heat the domestic water. An electric tank water heater costs about 1/3rd as much. It won't last as long as a quality indirect will, but for the money...
    Came across this article which talks about supplementing a tankless heater with a small electric tank. http://www.chandlerdesignbuild.com/files/fhbDecJan08.pdf

    Curious if this is what the suggestions above are indicating. The tank is simply keeping a supply of hot water. It's accomplishing the same thing as the indirect but using less efficient electricity (rather than gas of the indirect) to keep the water warm. Is that correct?
    #1 is a small (under 10 gallon) electric tank which helps with small draws and recirc systems. #2 is what I described.
    A plumber told me that to do the indirect, it would require removing the use of Outdoor reset since the boiler would need to run to 180 degrees. that sounded really odd to me. I may have misunderstood. Does the boiler need to run at 180 in an indirect configuration?
    The boiler will switch from ODR to full output (180°F or whatever you set) when there is a DHW call.
    >would it make any sense simply to get a electric hot water heater to keep it completely separate from the boiler?
    That depends completely on your energy costs and use patterns. Remember that a typical tank type electric water heater only has about 15,300 BTU/hr of heating capacity.
  • Leon82
    Leon82 Member Posts: 684
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    Since you are selling the house you may not see a complete return on investment for an indirect.
    The electric would be the easiest.
    you could do nothing and credit them at the closing also.
    Assuming the install is acceptable you are doing nothing wrong from leaving it as it is now.
  • jeanc
    jeanc Member Posts: 18
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    Leon82 - Install is good. I had thought that a good inspector should catch that and make a note and I could give a credit. So that's a good point. I suppose it would be a little risk if that held up anything.

    Thank you SWEI for the explanation. In looking at general costs, it appears that that the cost of on electric is $X and gas indirect $4X. Is the installation of each different... one more laborious than the other?

    The other part I didn't quite understand is the difference between that configuration #2 in the article of attaching the tank to the boiler vs. a completely separate heater. It sounds like from the thread that the the standalone electric may not have the same recovery since there is less BTU?

    But finally, the other big concern is the tax of anything attached to the boiler is how that effects heating. My boiler runs near constantly when it's cold. How long would the boiler go off approximately to heat 40 gallons?
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,542
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    On LI with 23c Kwh, no one wants an electric HWH in any form
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Paul48
    Paul48 Member Posts: 4,469
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    In CT, we had to pay for shutting ours down, after they ran it into the ground. We also had to pay for bad investments they made. Those were concessions our lawmakers made to them, so they wouldn't fight de-regulation. Hmmm......I wonder why we pay on a KW/H basis for them to deliver my electricity. It's not like there's a guy riding back-and-forth on a bicycle.
  • SWEI
    SWEI Member Posts: 7,356
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    jeanc said:

    In looking at general costs, it appears that that the cost of on electric is $X and gas indirect $4X. Is the installation of each different... one more laborious than the other?

    An indirect water heater is not "gas" per se -- it just takes its heat from the boiler water and uses that to heat the domestic water.
    The other part I didn't quite understand is the difference between that configuration #2 in the article of attaching the tank to the boiler vs. a completely separate heater. It sounds like from the thread that the the standalone electric may not have the same recovery since there is less BTU?
    I think for what you have that an electric tank water heater repurposed as a buffer tank is probably the best option.
    My boiler runs near constantly when it's cold. How long would the boiler go off approximately to heat 40 gallons?
    Without knowing the specifics of your house and the boiler, I can't really answer that in detail. The average additional load on the boiler will only be to cover the standby losses in the tank, which are quite small. It will provide a much better experience for the residents and (assuming you're not buying very expensive propane) cost far less than an electric tank will to own.