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Aquastat on a steam boiler

Greetings,

I heat my home with an oil burning steam boiler, by which I am trying to indicate that it is steam going to my radiators, not water. I also run my hot water off of the boiler.

At what temperature should I be setting the aquastat? What are the pros and cons of setting it higher or lower?

Thanks,

George

Comments

  • Jamie HallJamie Hall Posts: 8,374Member
    The aquastat is controlling the temperature of the hot water -- not the steam (that is controlled by a pressure controller on the boiler -- which should be set to no more than 1.5 psi). If this is a hot water coil in the boiler itself (that is, no indirect tank) you need to have a mixing valve on the hot water output, to avoid scalding people. The aquastat itself should probably be around 140, in my opinion -- if you have the mixing valve.
    Jamie



    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.



    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • LanceLance Posts: 93Member
    You may set your aqua stat like a water heater. the advantage you have is if you add or have a mixing control and flow regulation you can maximize your hot water coil output supply to meet your needs. Probably achieve an unlimited supply of hot water at least 3 GPM. BTU input and coil size will determine maximum potential.
  • Jamie HallJamie Hall Posts: 8,374Member
    I might add to all this -- you need the mixing valve. Period. Regardless of what you set the aquastat to. Reason being that when the boiler is actually making steam, the hot water coming out of that coil will be really hot, and very dangerous.
    Jamie



    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.



    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • EBEBRATT-EdEBEBRATT-Ed Posts: 4,080Member
    Set the aquastat as low as possible to minimize fuel consumption. If your shower is cold turn it up 5 degrees at a time until your happy. The hotter the boiler water the more hot water you get but the more fuel you will burn.

    The mixing valve is very important. Set the aquastat at 140 for starters as @Jamie Hall mentioned with a 5-deg differential (if it's adjustable) and the mixing valve to provide 120 deg water
  • georgede54georgede54 Posts: 5Member
    Thanks to one and all for your responses.
    It is a hot water coil in the boiler itself. I have no separate tank that delivers hot water in the house.
    Believe it or not, I have been told that I do not have a mixing valve.
    My system has been set up so that right at the boiler the hot water pipe coming from the boiler is joined with a cold water pipe, which I guess enters the house from the street.
    There is a lever that allows me to determine how much cold water gets mixed with the hot water coming the boiler before the mixture heads up to the apartments.
    A contractor friend of mine told me that this is NOT a mixing valve.
  • gfrbrooklinegfrbrookline Posts: 96Member
    Sorry to but into this thread but I have a similar set up except the coil feeds a hot water loop and a take off feeds a Superstor tank. Should I also set it at 140? I always thought I had to keep it higher to fend off bacteria. I do have a mixing valve and keep it at 160.
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