Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Why pipe indirect hwh with 1.25\" if fittings are 1\"?

hrhr Member Posts: 6,106
in many indirects that limit how many btu's you can safely push through. Most manufactures have this info in their installation, and often websites. Not a lot of sense in over piping if the limitation is in the coil. Ideally you would calculate the pipe size based on flow, distance, fittings, etc.

Some indirects can handle larger fows. tank in tank or the reverse indirects like Ergomax and Thermomax can handle larger flows. You will see these with 1-1/2 or larger connections.

A `circulator with an built in flow check is another way to prevent ghost flow. depending on the piping arrangement, you may need a check on both supply and return. Generally it is a good idea to use both checks with PS piping.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"


  • David107David107 Member Posts: 1,189
    I know it's supposed to get more flow but

    some installers have said, "fitting is only 1 inch; what's the point?"

    Also is it standard to install a swing check (or flow check?) and a Hydrotrol on the supply and return of the indirect tank to prevent gravity circulation?(and piping standby losses in non-heating season?)


  • MitchMitch Member Posts: 549
    pipe size

    If I get your question right you are asking why run a larger pipe up to a devise with a smaller tapping.

    Answer is restriction over distance.

    Think of a 100 foot power cord to a tool and 25 foot cord of the same gage, if you run the tool alot the 100 foot cord gets hotter than the 25. Same principle in piping.

    Mitch S.

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Brad WhiteBrad White Member Posts: 11
    I would

    go "conection size plus one", absent other direction. As Mitch suggests and to paraphrase as I may, why eat up delivery energy on the trip? Save it for the device. In short, the running pipe size should be based on flow and assumed velocity and pressure drop as for any pipe in your system. If the connection side falls in that range, great. My experience is to kick it up a size, but always check against flow rate just the same. Short runs are one thing of course; a few feet may not matter. But check you must.

  • David107David107 Member Posts: 1,189
    this was for Buderus ST-200

    which has these stats:
    1-Boiler water flow rate: 17.6 gal/min
    2-Coil Pressure Drop: 4.3ft of head;
    3-Boiler water supply and return: 1"
    4-Domestic HW outlet: 1"
    5-Cold water feed/dom HW drain: 1.25"
    6-P&T Recirculation return: 3/4"

    Doesn't say coil diameter. I guess I'll assume it's 1". Can't say any long distances are involved; I guess installers try to make run as short as possible. I assume the 'connection plus size one' here would be for boiler water supply and return. The small house involved probably has a domestic supply size of 3/4 or 1" maximum.

    Thanks as always, gentlemen.

  • Brad WhiteBrad White Member Posts: 4
    That would cement in my mind

    using at least 1-1/4" piping. My design charts and experience would have that at 1-1/2" for that flow rate.

    1-1/4" type L copper pipe at 17.6 GPM would have a velocity of about 4.5 FPS and a pressure drop of 7.7 feet per 100 feet of pipe. Say you have 25 equivalent feet (some pipe and several fittings), that is about 2 feet of loss right there.

    If 1-1/2", velocity drops to 3.0 FPS (nice) and pressure drop is reduced to 3.35 feet per 100 feet of pipe. All things being equal your pressure drop is less than a foot.

    Borderline, your call. You pay for the copper only once, remember.
  • David107David107 Member Posts: 1,189
    Muchisimas Gracias, Se
  • hrhr Member Posts: 6,106
    Do you have enough boiler hp to drive those numbers?

    If the boiler cannot drive that flow rate, not much sense in useing large diameter tube. Priced type L copper lately?

    Isn't the ST200 a 53 gallon tank? What kind of recovery do you need?

    hot rod

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • David107David107 Member Posts: 1,189
    sorry should have given full info before--it's for buderus

    G-115-21, which fires at 84K, outputs at 74Kbtu and nets at 64Kbtu. ST-200 tables says at 194deg boiler water temp, continuous rating (with inlet at 50deg, outlet 140) tank can give 199 gph @149K btu/hr. This is where alot of installers have told me, well look how high your HW heating load is--using the 149K figure--you need a big boiler. To which I say--hopefully having learned correctly from the wall--"that would be for hot water on demand without storage. I need not oversize the boiler to fulfill hot water needs; size boiler on heat loss--47K/100K gain and use storage to give HW." This house has two bathrooms--one has shower, the other a tub/shower, kit, basement sinks, washer, dishwasher. house currently has single occupant who has company over once in awhile. The worst case scenario will never happen--simultaneous bath and shower, dish and washloads, though at some point a family may buy it we know.

    I believe the contractor, in order to keep things simple, specked the large 53 gallon in order to be keep the HWH temp at 125 and go staight into the domestic supply at that temp to avoid having a mixing valve. (probably not a great idea, both re: Legionella or hot water capacity sake.)


  • hrhr Member Posts: 6,106
    Save your copper dollars

    1" copper will move all the btus that boiler can muster to the indirect. Run a 30 degree delta T and 3/4" would be adequate.

    Yes, you would be wise to run the indirect tempersature higher for extended DHW and legionella issues. Use an approved mixer if you go above 140 for scald protection. 53 gallons of 120 water doesn't go far.

    hot rod

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • David107David107 Member Posts: 1,189
    you mean 30 deg delta T between tank water temp and domestic

    supply? or between boiler supply temp and indirect aquastat setting?

    also type M copper is acceptable,yes?


  • Brad WhiteBrad White Member Posts: 188
    Type M

    Would be acceptable, David. The recent price escalation had me taking that option for the first time. Type L was always my way until now. Slightly better flow characteristics (thinner wall = larger ID). And the cost is a bit less painful.

    Hot Rod brought up an excellent point on looking at the "system", not just the heater itself. Your drop in capacity means longer warm-up times to temperature, that's all.
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!