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DHW Options

ChrisL Member Posts: 121
I am looking to replace a 100 gallon 199,000 btu hwh. I am looking into more efficient options than the typical gas fired hwh. I am looking into the tankless water heaters, which have the nice advantage of no standby flue losses. However, I have the hot water lines on almost constant recirculation since its a multi-unit apartment building. It seems to me this would result in short cycling on a tankless since there is no storage buffer. Has anyone dealt with this issue? I suppose I could put a 40 gal tank in the circuit. Anyone have any real life experience with $$ savings with a setup like this?


Chris L


  • John@Reliable
    John@Reliable Member Posts: 379
    Sounds like you should ,

    look into some indirect water heater(s)
  • James_2
    James_2 Member Posts: 24
    Most of the apartments are

    using copper-fin boilers with storage tanks. Definitely an improvement over tank style water heaters. If your planning a long term investment look at the Munchkin boiler with an indirect tank.
  • ChrisL
    ChrisL Member Posts: 121

    Thanks guys. I am considering a Munchkin/Indirect combo. Its just that for strictly making DHW, the condensing efficiency of the Munchkin is wasted since it will have to run boiler temps in the 160-180 degree range. It seems to me an instantaneous water heater setup would be a little better from the standpoint of cost, assuming I can include some storage of water for buffering.

    Chris L
  • Dan Peel
    Dan Peel Member Posts: 431
    Do the math

    If your peak flows @ temperature can be met by the wall hung selected alone then fine, if not you'll need storage. The wall hung can still ramp and condense if it's shooting for 180 - just give it a taste of the cold input water and work through a buffering tank instead of going the indirect route. Enjoy.....Dan

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  • JackFre
    JackFre Member Posts: 225
    Rinnai Continuums

    First the disclaimer, I represent Rinnai. Definite bias but let's let the numbers do the talking. The Continuum will modulate from 15,000-180,000 btu. Minimum flow rate of .5gpm to max of 8.5gpm. Energy factor 82 on nat'l and 87 on LP. Sealed combustion, direct vent. A 60degree temp rise will yield 5.2gpm, 70 deg yields 4.5gpm...all day long! Night too.

    How many apts? What is the layout of the building? Gas type? What fixtures are in each apt? Laundry? How many machines? Rinnai's can be used singly or manifolded together to increase flow capacity. Can be used to heat storage also, if you desire. Recirc is not a problem.

  • ChrisL
    ChrisL Member Posts: 121
    re: Rinnai

    Thanks for the reply Jack...just the person to answer my questions. This would be for a 10 unit apartment building, all with 2br. apartments. There are 2 washers for laundry.

    Since this job would probably require more than 1 unit, what sort of controls are available for piggybacking? Also, would the burner modulation eliminate the need for a buffer tank when the recirculating pump is on?


    Chris L
  • corey
    corey Member Posts: 45
    maybe not wasted

    I recently asked HTP about this.
    The Munchkin still runs at 92 percent efficiency with 180 degree supply and 140 degree return. This is still somewhat better than near condensing. Unfortunately, they were not able to provide any hard numbers for other operating temps, just that efficiency would improve for lower temps. For the record, I run mine at 160 degrees, and still get substantial condensate out of the drain.
    I wonder if for DHW only, something like a Polaris 50 gallon 199,000 btu condensing water heater(or similar) might be easier and cheaper to implement than an indirect scheme.
    6.4 GPM Recovery Continuous @60degree rise.
    7.0 GPM First hour @60degree rise.
    If 50 gallons is too little reserve, a storage tank could be added.

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