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One boiler or two?

Tweets55
Tweets55 Member Posts: 4
edited September 2020 in Gas Heating
Hi, I'm looking for advice on which is better: one boiler (285K BTU/gas) for two, 60 gallon indirect water heater tanks OR
two boilers (each 199K BTU/gas) for two, 40 gallon indirect water heater tanks. We have 5 1/2 bathrooms.
Thanks very much for any help!!

Comments

  • STEVEusaPA
    STEVEusaPA Member Posts: 5,321
    edited September 2020
    Is this just for domestic hot water? Whether it's one or two boilers, probably just one larger indirect. Unless the house is so big that the bathrooms are on opposite ends of the house.
    steve
  • mattmia2
    mattmia2 Member Posts: 3,991
    2 boilers cascaded gives you redundancy so you still have some hot water if one fails. They could also possibly be smaller that way.
  • Tweets55
    Tweets55 Member Posts: 4
    sTEVEusaPA Yes, domestic hot water. And yes, the bathrooms are all over the place. So sounds like two boilers might be best.
  • Tweets55
    Tweets55 Member Posts: 4
    mattmia2 I don't know what Cascaded means.
  • mattmia2
    mattmia2 Member Posts: 3,991
    Both boilers supply common heating piping, if the load is low enough for one boiler to pick it up, only that boiler fires, if one boiler can't produce the needed capacity the other boiler fires. That does require piping between both boilers and tanks but it means if one of the boilers fails the other one can supply both tanks at reduced peak capacity. It can be done with modulating or conventional boilers. Most modulating boilers have the control built in to connect 2 together. Usually there is a primary loop that all of the devices connect to with separate circualtors and the circulator for that boiler or water heater only runs when it is active.

    This is the general idea using low loss headers to combine the boilers and different loads together:
    https://baxi-public.partsarena.com/Documents//DOC_004996/920D230CD6B831FD7D2FA3BDC19476858662C03AE023A60B5EBDBD574D8FEF9AE77ECD357AA3758B1A2FCEF8C13A303D4D55DCD5B8A4EE872DE73729181E6B7F.gif
  • Tweets55
    Tweets55 Member Posts: 4
    edited September 2020
    STEVEeusaPA and mattmia2 - THANK YOU both for your comments. We've just talked it all over with the family and we've decided to go with two boilers and two water heater tanks! All the best. Tweets
  • HVACNUT
    HVACNUT Member Posts: 4,209
    So in one hour and twenty five minutes you posted a question, had a family meeting, and made a decision. Excellent job! Does anyone in the family happen to be a heating contractor? He or she might have some input. What are you using for space heating? I frequently service 20+K sq ft homes and the necessity for a dedicated boiler strictly for domestic is extremely rare. However, all large tubs and rain heads have their own heaters.
    mattmia2STEVEusaPAAlan (California Radiant) Forbes
  • mattmia2
    mattmia2 Member Posts: 3,991
    edited September 2020
    I thought about pointing out that one or 2 large commercial water heaters will cost them far less than any energy savings they will ever get by using a boiler and indirect in this situation...

    In fact HTP makes a number of both large and high efficiency water heaters.
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,321
    I wouldn’t put in boilers an indirect just for domestic hot water in a home.
    steve
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,355
    The first step is the step that is missing.

    calculate the hot water demand
    mattmia2