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Installing Tankless Coil on Hot-Water Boiler to bypass Water Heater

AlexPetronAlexPetron Posts: 13Member
Hello. On a 25-year old gas-fired hot water boiler, as is the one seen in the attached picture, which serves a radiant heating system, is it possible to install a tankless coil providing domestic hot water in order to bypass the existing Rheem water heater?


Comments

  • HVACNUTHVACNUT Posts: 1,600Member
    Tankless coil in the boiler? No. You do an indirect water heater as another zone, or a tank piped using a plate HX.
    Re piping must be done.

    It is that flue reduced to a power vent? Can't tell.
  • IronmanIronman Posts: 4,585Member
    If you wanna see your fuel bill increase 40%, then you could do a tankless coil. The block would have to have provision and you'd need a triple aquastat.

    Go with an indirect if you wanna get rid of the water heater.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • bob eckbob eck Posts: 777Member
    How old is the boiler? Do you have natural gas or LP gas?
    If that is a cast iron gas boiler most likely it will not have an opening for a domestic coil and if it does bad way to make domestic hot water because the boiler water will need to be kept hot 24/7/365 just to take an shower. Not very efficient way to make domestic hot water.
    You could do and indirect water heater with this boiler. Vaughn has a indirect water heater that you can get electric elements in the IDWH that way you could use the boiler to make hot water or electric.
    If the boiler is 25 to 30 years old you could look at installing a condensing combi boiler that will do heating and domestic hot water all in one unit and it vents sidewall with PVC, CPVC SCH 80 or Polypropylene vent pipe. You could also install an condensing gas boiler with an IDWH tank.
    If you have natural gas is your gas utility company or the state that you live in offering any type of rebate to home owners?
  • EBEBRATT-EdEBEBRATT-Ed Posts: 4,512Member
    your boiler has no opening for a tank less coil and you don't want an external tank less. install an indirect tank
  • EbenSEbenS Posts: 4Member
    I have a similar question - I'm probably replacing my boiler (Weil-McLain CGa-4) and wondered if I should pony-up the extra to shift to a system with 'domestic' or a combi-unit? I live in southern Virginia if that makes any difference.
  • bob eckbob eck Posts: 777Member
    How old is your current boiler? Is it leaking? How do you make you hot water?
    You could replace the boiler with a similar gas boiler or you could use an combi boiler.
    Get a heat loss done on the house so you get the correct size boiler installed because if the boiler is to large the boiler will short cycle.
    If you put a condensing combi boiler in and if the boiler does not condense using low water temps to heat your house the condensing boiler is not the one to go with.
    Find a professional heating contractor that does boilers in your area and they should be able to give you options.
    Good luck.
  • IronmanIronman Posts: 4,585Member
    A mod/con with an indirect water heater is almost always a better option vs. a combi unit.

    I'm near Staunton, where are you?
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • bob eckbob eck Posts: 777Member
    Ironman why do you consider an condensing gas boiler with an indirect water heater better than an combi boiler?
  • IronmanIronman Posts: 4,585Member
    bob eck said:

    Ironman why do you consider an condensing gas boiler with an indirect water heater better than an combi boiler?

    Several reasons, but the two that come to mind first:
    1. It's usually very difficult to find a combi that meats BOTH the demand of space heating and domestic. If sized properly for domestic, it's usually severely over-sized for space heating.
    2. Combi heat exchangers clogg quickly in places with hard water. This is what most of our ares has - hard water. By the time a HO has to pay for descaling a couple times a year, the combi is not such a great bargain. Water softeners are not good for the human body and by the time that's added to the cost of a combi, they could have had a properly sized boiler and indirect.

    I try to make sure that any system that I design and install has as minimal amount off issues as possible.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • bob eckbob eck Posts: 777Member
    Ironman have you used the Aquapure AP430SS filter in the domestic cold water inlet side of combi boiler when there is hard water? This filter helps keep the domestic side of an combi boiler from building up with lime scale.
    The Lochinvar Noble combi boiler on the heating side you can derate the boiler to meet the house BTU load for heating and when the boiler fires it will go to high fire to make sure the boiler is firing hard enough to produce domestic hot water.

    There is nothing wrong with an condensing boiler with an indirect water heater.

    I wonder if any contractors that are installing condensing boilers, regular gas boilers, or oil boilers and use an indirect water heater are they installing any type indirect water heater with electric elements in the tank so when the boiler breaks down the electric elements can still heat the water while the home owner is getting an contractor to fix the boiler. At least the home owner will still have domestic hot water.
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