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Indirect Water Heater

If anything, I'd be inclined to increase the storage capacity of the indirect before I increased the size of the boiler.

The proportion of surface area (where heat loss occurs in an indirect) doesn't grow as fast as volume, but the efficiency "hit" from a higher low-end modulation rate grows more rapidly the farther away it is from the point where you need no heat in the structure.


  • Tim B.
    Tim B. Member Posts: 1
    Indirect Water Heaters

    Hi Everyone. We have a new radiant floor staple up with plates install. The system also has some baseboard in the garage and sun room. Baseboard will run 180 max on outdoor reset. Some brand of condensing gas boiler will be installed, so far, I like Munchkin the best. Radiant floors will be mixed down to 115 max and they will of course be on outdoor reset as well. An indirect will be installed for DHW. Now, Munchkin boiler are self-modulating. However, if a boiler wasn't and your heatloss was right on the line between two boilers, how do you add size to a boiler to allow for an indirect?
  • hr
    hr Member Posts: 6,106
    I guess it would depend

    on how wide the spread was. If the load is 75K and the choice would be a 60 or a 100K non modulating, I'd go with a larger and a buffer tank, maybe a combo buffer/ DHW, like an Ergomax to get double duty.

    It is possible, in some areas, to be at, or maybe below, design temperatures for days or weeks. You don't want to cut too close unless you have a supplemental system, like FA.

    hot rod

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