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Steam boiler: aquastat setting?

pils Member Posts: 6
Hi folks

I have a one-pipe steam radiator system using oil in New England. Until this summer, the boiler also provided on-demand hot water; however, we installed a Steibel Eltron heat pump system to get off oil for hot water.

We recently had the yearly maintenance on our system and the tech ended up disconnecting the aquastat that controlled the temp for hot water. My question is: In terms of energy efficiency, is it better to have the water temp maintained at certain temp even though we don't need the boiler for hot water? And if so, at what temp?

It seems that the boiler is running longer to make steam than it was when the aquastat was hooked up - which makes sense since the water is likely not as hot. So - ss it more energy efficient to maintain a certain water temp (the burning turning on occasionally to heat water although our thermostat is not calling for heat) or to heat the water from a lower temp for steam ONLY when our thermostat calls for heat.

Many thanks!


  • Jamie Hall
    Jamie Hall Member Posts: 23,526
    It's a toss up, and depends a lot on the mass of the boiler, the amount of water in there, the insulation of the boiler, and how often the thermostat calls. You would have to accurately measure the running time of the burner at several different outside temperatures (which affect how often the thermostat calls) with it set up both ways to find out. There won't be a cut and dried answer.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUT Member Posts: 5,870
    IMO, leaving the aquastat disconnected during the heating season will extend the burner cycles, making it more efficient.
    I would however leave the aquastat, disconnect one wire only (low volt right?), and reconnect it during the non heating season, setting it at 150 degrees with a 20 degree diff. I only suggest this because it's oil fired. If the boiler sits cold all summer, the flue passages become a mucky wet mess, and very hard to clean.
    EBEBRATT-Ed Member Posts: 15,721
    Your point will bring many answers and not many will agree with one another.

    Personally I would leave it disconnected. If your technician reports any problems on your next yearly service you can always have it reconnected. Minimum temp 130 deg (no one will agree on this either)