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Possible to use old cast iron radiators for low temp?

weil_fail
weil_fail Member Posts: 84
edited December 2023 in Radiant Heating
Are there any calculations for fans/airflow you need to get equivalent heat out of a cast iron radiator with water heated to 170F? For different water temps around 120F? Is it possible?

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,302
    If you are talking about cast iron radiators yes there are charts that show the output at lower water temps but fans have nothing to do with that. When you say "cast iron water heater" what do you mean?
  • PC7060
    PC7060 Member Posts: 1,135
    No need for active convection.  Just need enough radiators and tight enough envelope. I run a low temp system (116F SWT @ 11F outside temp) using original radiators in a 100 yo home.  
    MikeAmannRich_49
  • weil_fail
    weil_fail Member Posts: 84
    edited December 2023
    EBEBRATT-Ed, sorry for the confusing wording. I edited it. 

    I'm trying to how much fans add to the heat output of a radiator. Like, is it possible to add fans and lower water temp and get the same btu output 

    PC7060, I'm thinking of about the idea of lowering the temp in an existing system
  • PC7060
    PC7060 Member Posts: 1,135
    edited December 2023
    weil_fail said:
    PC7060, I'm thinking of about the idea of lowering the temp in an existing system
    Have you assessed the heat loss/gain of your house?  Determining the max BTU required on coldest day is the first step. 

    What type of boiler is currently in the system?  Condensing boilers work well in this application but cast iron boiler may require tempering of the return water to prevent corrosive condensation of exhaust gases in boiler or flue. 

    The changes in my system were limited to new modcon and additions of TRV for each radiator. 
  • Jamie Hall
    Jamie Hall Member Posts: 22,897
    weil_fail said:

    EBEBRATT-Ed, sorry for the confusing wording. I edited it. 

    I'm trying to how much fans add to the heat output of a radiator. Like, is it possible to add fans and lower water temp and get the same btu output 

    PC7060, I'm thinking of about the idea of lowering the temp in an existing system

    Well, yes it is -- but you have to direct the airflow over the radiator with shrouds to get any significant increase, and the work would be experimental. I know of no standard equations, never mind tables or designs. A fan blowing at an unshrouded radiator will have minimal impact.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    kcopp
  • weil_fail
    weil_fail Member Posts: 84
    PC7060, I'm just thinking generally about replacing high temp water boiler with lower temp heat pump

    Jamie Hall, unfortunate that there aren't guidelines 
  • jesmed1
    jesmed1 Member Posts: 551
    edited December 2023
    How do you know how much heat output you need? Just because the previous boiler ran high water temps doesn't necessarily mean you need to match that heat output. Many old houses with cast iron rads only need 120 degree water or less, because there's so much installed radiation. I live in one such old house where we can heat with sub-120 water throught the original cast iron rads. So do a heat loss calculation first.
    PC7060
  • hot_rod
    hot_rod Member Posts: 21,835