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Will a larger tankless coil fit in my boiler?

Big EdBig Ed Member Posts: 1,117
A bigger coil will not produce any more with out higher btu input..140000 btu input will produce 2 gallons per min..Give and take .If you want 5 gallons per min you better be firing 350000 btu input. and that's with out putting out to heat your home..A bigger coil will be useless.

You need a storage tank or hot water heater.


  • CharlesCharles Member Posts: 74
    It's a Burnham V7-5

    My old coil is very corroded and rusty, at least externally, and I'm probably going to replace it rather than aggressively clean it and risk a pinhole leak later. Anyway it's not keeping up with my shower, and I have a new aquastat that is working properly.

    I can't read what's left of the label but the manual for my boiler (Burnham V7-5) says it's supposed to be a V1-2 rated at 3.25 gpm. That would be enough when new, but as the scale and crud accumulates over the years I'd like a little reserve.

    Will a larger coil (V1-3 or -4) fit in the boiler? Do the higher capacity ones get longer, or have more fins/tubes in the same space?

  • Call these guys, they are the best..........
  • Jeff LawrenceJeff Lawrence Member Posts: 746
    I don't know

    if that's a HW or steam boiler, but using an indirect is a possibility.

    John's idea is good too.
  • CharlesCharles Member Posts: 74

    it's a one-pipe steam boiler.

    I just got an email back from TFI Everhot saying they only sell through wholesalers and distributors, and recommending a V1-5 which seems bigger than I'd need. I also asked about the fit of that larger coil, but haven't got a reply yet. May have to resort to the phone :)

  • CosmoCosmo Member Posts: 845
    I agree w/ Ed

    Though the bigger coil will give you more heat transfer as compared to a smaller coil after they both get full of crud. Is it worth it? Who knows......

  • NoelNoel Member Posts: 125
    Keep in mind this rule of thumbs

    For each GPM of coil output, you need 50,000 btuh of boiler OUTPUT. A bigger coil isn't the same thing as a bigger fire.

    As Dan says, "It's like the ATM machine... You can't take out more than you put in."

  • CharlesCharles Member Posts: 74
    Thanks for the figures...

    > Though the bigger coil will give you more heat

    > transfer as compared to a smaller coil after they

    > both get full of crud. Is it worth it? Who

    > knows......


    > Cosmo

    At what temperature differential is that 50k BTU/hr/gpm?
    The water coming into the coil is pretty cold in winter, say 50 degrees this time of year. But is the output temp specified at 120, 140, or what?

    I was indeed looking to improve the heat transfer as the coil cruds up with age, but hadn't considered that the fire size itself might be the limiting factor!

    If I take the output of the coil and feed it into a storage tank, how do I keep it hot - a connection back to the coil? If I need to hook up electricity (such as a conventional water heater) I might as well do away with the tankless coil entirely. The water heater would probably be as cheap as the coil anyhow...

  • CosmoCosmo Member Posts: 845
    what I meant

    was that given the same boiler btu's when they both start to get dirty on the outside, the larger one will have a larger heat exchanger and may give you the same gpm hot water as the smaller model but may do so even when kinda dirty.

    You and the rest of the world are better off installing indirect water heaters. Forget about the (dang good fer nothin except that its cheaper) coil.

  • Big EdBig Ed Member Posts: 170
    Thanks For The Up Date

    Thanks Noel for the reminder . I forgot your rule of thumb for newer boiler outputs.

    Noel , you still working up in Greenvale ?
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