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Return water temp on indirect water heater

Should I install a 4 way mixing valve on the boiler return water from my indirect water heater? The indirect is located 60' from the boiler. 1" supply and return lines will be insulated and travel through cold basement areas (45-50 degrees during winter months). My concern is that when the water heater has no demand and sits for hours before calling to maintain temperature that the circulation lines will have cooled down substantially enough to cause flue gas condensation. I would think that the return water will reach 140 degrees in less than a minute of circulating, would running it like this be bad for the boiler in terms of flue gas condensation?

Thanks

Comments

  • Zman
    Zman Member Posts: 7,328
    Any cold start boiler will condense a bit at start up. As long as the cycle is long enough to dry the flue it won't be a problem.
    In cases were the indirect is over sized the boiler, you can have condensation damage do to long exposure to condensing temps.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • HVACNUT
    HVACNUT Member Posts: 4,590
    edited December 2017
    I
  • jac70
    jac70 Member Posts: 3
    Thanks for the reply Zman.

    I don't have a cold start boiler. Traditional cast iron boiler maintaining 160-180 degree water temp.

    According to the tekmar specs (741 actuator) on the 4 way mixing valve, it takes 65 seconds to fully open. I'm guessing the return water temp will be at 140 by the time the valve opens enough to allow for a proper mixing temp.

    Maybe I'm completely off on this and the temperature in the well insulated supply and return lines won't drop below 140.







  • HVACNUT
    HVACNUT Member Posts: 4,590
    Is the aquastat a dual or triple acting?
    Dual will maintain the high limit, the triple will maintain low limit and cycle to high limit on a heat demand.
    If the piping is well insulated, it shouldn't be a problem.

    Somebody please clarify.
    I thought the problem of condensing flue gasses in a CI boiler was sulphur oxide.
    Now with ULSD, it's not a concern anymore.
    IMO, a cold start aquastat if fine on a CI boiler, if it has an indirect.
    I dont know if they still do, but Slant Fin used to supply an L8148A with the Liberty.
    Zman
  • Zman
    Zman Member Posts: 7,328
    I would not be concerned about condensing in your case, even if the water in those lines gets cold. Sustained condensing is the issue.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 11,989
    Nothing to worry about. Only the return line water will be cold and just what the return line contains.

    The cold boiler supply water pipe it's contents will be heated by the indirect (by reverse) & since your boiler is maintain temperature it will not be a problem mixing in a little cool water
  • jac70
    jac70 Member Posts: 3
    Thanks everyone for the advice!