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Oil Boiler - Summer/Winter Aquastat Settings

amin1992 Member Posts: 46
Hey guys, without going into crazy detail I have an older cast iron Oil boiler that provides both heat to the home and domestic hot water with an indirect coil.

Winter time, I've got the settings down pretty good on the original Honeywell Aquastat: HI 185F, LO 165F, and the DIFF at 15. Heats the house well and provides ample hot water.

When summer comes and I won't need heat, what do you think I should set this to to keep the hot water flowing for showers and such? I was thinking I could set it to HI 150, LO 130, and DIFF 25.

I just want to make sure the hot water can keep up, but also don't want to waste oil and don't want to damage the boiler by not keeping it hot enough.

Appreciate the help.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Confusion...I think the diff @ 25 and the 20° spread could be an issue in an older triple aquastat. The temperatures aren't always accurate.
    Bump the high limit up to 160° (it shouldn't hit it anyway) and see how it goes.
    I'd personally would want the temp over 140° and mixed down to prevent scalding.
    Insulate the hot water pipes.

    I'd also check that the boiler gauge, and the temperature of the water, and the setting on the aquastat are all the same, IOW, when the boiler hits the high limit, say 185°, does the boiler gauge and the water temperature match.

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