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aquastat setting with both fin tube and cast iron radiators

I have a 2800 sq ft three level converted barn home with four zones of hydronic heat. The boiler is a 28 year old New Yorker FR-122-W with a Honeywell LB124A aquastat. I have a summer/winter hookup.
When we built the house we were not able to find vintage cast iron radiators that met our budget and we didn't realize how much more comfortable radiant heat is. So ten years later when we finished the basement we found cast iron radiators and we loved it. Recently I came across vintage radiators for free and so I changed the main living zone from fin tube to radiant heat. Everything went well and we love the heat.
My question is: can we or should we change the temperature settings on the aquastat? Is there any saving to be had by doing so? During the heating season I set the aquastat at 180/160 .
The other two zones are used less frequently and heated by fin tube baseboard.


  • Jamie Hall
    Jamie Hall Member Posts: 22,887
    Probably no need to change the settings. Different temperatures will give you different heat output from the radiators -- but also change how much the boiler cycles on and off. If it's working for you, leave it be.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gilmorrie
    Gilmorrie Member Posts: 185
    What temp setting have you been using? If it has been running O.K I would leave it alone.

    A problem with mixing cast-iron and fin tube heat emitters arises because they have significantly different heat storage characteristics. Cast-iron baseboard units will continue to emit stored heat for a considerable time after a call for heat - resulting in more steady heat. Fin-tube units will stop heating the room quickly after the call for heat ends. Fiddling with the aquastat setpoint probably won't make much difference, either way, but you can try it. The optimum solution is to put the two types of heat emitters on separate zones - each with its own thermostat - which you already have done!

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,501
    edited October 2022
    You set the aquastat at 160° and 180°. Can I assume from that statement, you have a domestic hot water coil inside the boiler. We used to call that a Summer/Winter hookup because the oil burner would operate in the summer and the winter. The technical term is a "tankless coil". You will want to leave the low (160°) at the current setting. Any lower and you may end up getting cold showers. You always want the High Limit to be 20° higher than the Low Limit. so 180° is just right.

    I agree with @Jamie Hall and @Gilmorrie. "If it ain't broke... You know the rest
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics