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Indirect tank in the summer question

russiand Member Posts: 73
I am seeing a condition with my indirect that I don't quite know how to address. In the warm months when there is no call for heat from any zones other than the indirect, boiler water can get significantly colder than water in the tank. When the aquastat in the indirect calls for heat, there is a period of time when cold boiler water circulates through the indirect's heat exchanger, effectively robbing the indirect of its heat. In a mater of mintures boiler water obviously warms up and everything works as normal. Is there a way to delay circulation of water through a zone untill boiler water reaches a certain temp? In the winter this is not an issue since boiler water on average stays pretty hot. I am uzing a Taco ZVC with priority for the tank.

Thanks in advance.


  • Ron Jr._3
    Ron Jr._3 Member Posts: 603
    Very good question

    And one I used to battle with in the summer months with my Plus 30 indirect ( lotsa women in my home :)  )  .

    What type of aquastat do you have on the boiler ? What type of boiler ?  Worst case - you could add a single aquastat to the boiler to delay the indirect zone valve from opeining till the boiler water is hot . But you get the risk of running out of hot water that way also ........
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Indirect tank in the summer

    Before you spend any money solving this problem, make sure it is a problem. N.B.: I am not a professional heating contractor.

    I have an Ultra Plus 40 indirect-fired hot water tank. This holds a little less than 40 gallons of domestic hot water, and the water jacket holds 6 gallons. The boiler holds about 3 quarts of water and the piping between the two hold perhaps a gallon or so. Call the whole thing 8 gallons. Unless I use a lot of hot water (I rarely do), this means the boiler fires once or twice a day for less than 10 minutes each time.

    The way my boiler is set up, the domestic hot water heater is primary, but it does not matter in the summer. The boiler is set to run 160F water into the water heater that is trying to maintain 125F hot water. When the heater asks for water, the circulator turns on immediately and the fire comes on pretty quickly. Since the boiler consumes 80,000 BTU/hour input, it can heat the gallon or two of cold water pretty quickly. Meanwhile, of course, the cold water is going into the hot water heater, but the heat from the hot water heater is not really wasted, since it means the boiler water comes up to temperature all that much quicker. (The pipes between the boiler and the hot water heater are insulated.) So I would imagine the only heat wasted would be that lost from the boiler itself, and it is pretty small (holding less than a gallon of water). Also, due to the design of my boiler, the manufacturer  insists on running the circulator anytime the boiler is firing.

    Last summer I burned 3.15 therms per month for my boiler and (nominal) 40 gallon hot water heater, but I do not use a lot of hot water (no women in the house).
  • Steamhead
    Steamhead Member Posts: 16,893
    If your boiler is piped primary-secondary

    you can put an aquastat on the primary loop that will cut off the indirect circ until the primary is up to 110 degrees or so. 
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • 1maytech
    1maytech Member Posts: 1
    System 2000

    You can install a System 2000 boiler. It will not circulate water until it reaches 140 degrees. Also it will probably cut your heating bills by at least 30%. Now you can add on a solar package for domestic hot water and save even more and get rebates to boot!

  • russiand
    russiand Member Posts: 73
    I have a regular L7224U on the boiler

    With low diff disabled. The boiler is not piped primary secondary.
  • toilburn
    toilburn Member Posts: 44

This discussion has been closed.