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indirect water heater sizing

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Rob_30
Rob_30 Member Posts: 7
1) I see the Phase 3 has a 1" supply/return. If it was instead, say, 3/4", would there be any benefit in running the same diameter as the header (say 1" to 1.25") right to the indirect?

2) With larger capacity tanks for dump loads and higher gpm flows, won't the recovery time really stretch out for a small boiler with a largish indirect? Or is the idea to so fully cover the dump load that you don't get tepid water during recovery or soon after the dump load? (ok, that's three questions...). My mind's eye is seeing a 60 gal tank full of ~80F water needing a long time to get back to 120-140F if a small boiler. Want to understand better. Thanks!

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  • ddenny
    ddenny Member Posts: 75
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    indirect water heater sizing

    has anyone put in anything smaller than a 30 gallon water heater in a single family house. seems like no one wants anything smaller than a 30 but that seems like a little overkill to me. especially for people who have been satisfied for years with a tankless coil. anyone had good results with a 20 gallon capacity. I know there isn't much difference in cost between a 20 and 30 gallon but it's got to be a little more expensive to run yes? no?

  • kevin coppinger_4
    kevin coppinger_4 Member Posts: 2,124
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    Amtrol has....

    26 gallon that has worked ok for some. It all depends on your water usage. I know a former employer tried to do the 20 gallon SS w/ a mixing valve...didn't work out so hot. My parents have a 30 and it works fine...

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  • ScottMP
    ScottMP Member Posts: 5,884
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    I would'nt go any

    lower than a 30 with a tempering valve. One bath home with a small family. For tha added cost I don't think a 40 is that much of a change

    Scott

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  • 1974bobcat
    1974bobcat Member Posts: 18
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    Think about this

    Ok so you have a 20 gal tank and lets assume all the water is hot. Now you hop into the shower with your 2.5 gpm shower head and get an 8 minute shower. Here's the best part no one else can shower after you because the tank is still trying to recover. I never put in a tank smaller than 45 gal on an indirect. The superstor only looses 1 degree an hour.

    Bob
  • hot_rod
    hot_rod Member Posts: 22,158
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    I have a 32 gallon Phase 3

    in my home, powered by a 80,000 Lochinvar Knight. It provides an endless supply of DHW to my shower.

    Keep in mind my well doesn't fall below 60F as input water temperature is important for DHW production.

    It must be piped to allow the full output of the boiler. Generally 1-1/4" maybe 1" if the run is short and fitting free :)

    I like this better then the instantanous heaters for efficiency, longevity, and a bit of storage should the power go down.

    Larger capacity tanks will provide dump loads, if that is important. Large gpm flows, etc.

    hot rod

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 22,158
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    yes, there is no free lunch

    DHW is a load just like the heating system. The larger the tank, the longer the recovery.

    It's not uncommon with todays well insulated homes and hot water hungry Americans :) to see the DHW load numbers exceed the heat load numbers.

    You need to size the boiler to the largest load, regardless.

    But the first step will ALWAYS be to define the loads, both the heating and the DHW.

    Define how many gpms of DHW, the length of time, and how much dump to fill a large tank.

    Then either store that much, or generate it at the rate you use it.

    Perhaps a large tub dump load could be easier handled with a point of use instantanous. Then size the indirect for the remaing load.

    It's all hypothetical until you put some numbers to the question.

    I'd also highly recommend solar DHW preheat be added. Several manufactures now build dual coil indirects for solar and boiler inputs. If you have large DHW loads solar payback could be short, under 5 years then money in the bank :)

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • CC.Rob_3
    CC.Rob_3 Member Posts: 33
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    excellent

    Thanks. Solar DHW/preheat (and possibly heating integration) would definitely be the next step here. Have always been curious about the basic indirect design philosophy in general, though.
  • Chris_82
    Chris_82 Member Posts: 321
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    We have replaced many smaller units with larger units throughout the years. Never the other way!
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