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DHW - new tankless or from boiler?

Scott Denny
Scott Denny Member Posts: 124
I have a Rinnai question. If both the 3532 and the 3520 have a maximumn burner rating of 180MBTU, how can the 3532 produce substancially more hot water than the 3520?


  • Pete_18
    Pete_18 Member Posts: 197
    NG tankless vs. using steam boiler

    I have an original Bosch Aquastar tankless unit and while I love the unit, I would like something with more capacity (mine is a smaller unit that can really only handle 1 fixture at a time). I would like to eliminate the standing pilot.

    I have never been a big fan of hot water tanks, so I was thinking of going with a Rinnai 2532 tankless unit.

    Would I be be better off with using the steam boiler instead w/ tankless / indirect?

    I know it isn't great for the boiler to cold start, but at the same time, it pains me to think that I would need to waste oil all summer long for a relatively small amount of DHW.

    Important factors would of course be upfront cost, annual cost to run, life expectancy and amount of hot water output.

    If it matters at all in the mix, I would like to eventually add a radiant floor zone w/ a heat exchanger to the boiler.

  • Al Letellier_9
    Al Letellier_9 Member Posts: 929

    You can't get much more efficient than a tankless gas heater for making hot water. The unit you mentioned is an excellent piece and we install lots of them. It only heats water when you need it, will provide up to 8 GPM of continuous hot water ( 3- 2.5 shower heads non-stop ) and will not put a load on the boiler in the off-heating season. The less fuel you use the better. The Rinnai would be my choice...a no brainer !!

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  • JackFre
    JackFre Member Posts: 225
    As to the output...

    I represent Rinnai in New England. The 2532 (R85)is an excellent unit and is capable of 8.5 gal max output. The less expensive 2520 (R53)has a max flow thru the unit of 5.3gpm. You must check your ground water temp however to see what your rated/true output will be. Both units have the same size burner. At a 70f temp rise (50-120) both will make 4.5gpm all day long. You will not realize the higher flow capability of the R85 unless you live further south where the ground water temp is higher and hence the temp rise requirrement is less. For instance in FL you get almost 80F ground water so the Rinnai will only need to bump the temp 40F. You will see 8gpm in that case. If you live in the north, buy the less expensive 2520. Check with utilities for rebates and there is a Fed tax rebate for those who qualify.

    Al, you going to be in Hartford this week? See you there?
  • JackFre
    JackFre Member Posts: 225
    Given that both burners are identical

    it is a matter of flow and temp rise. (on anyones on-demand it is all flow and temp rise...always) The 2532 HX was designed to allow a cold water mix with the HX outlet water to arrive at higher flows...but then, necessarily lower temp rises. Check out www.rinnaisolutions.com for some good engineering data.
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