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Temp of Cast Iron Radiator

derbyct Member Posts: 4
I have a hot water radiator heating system. I am measuring the temperature of each individual radiator. Some of the radiators are lukewarm, barely 80. What should the temperature of a properly working, fully heated cast iron radiator be?


  • Weezbo
    Weezbo Member Posts: 6,232
    edited November 2013

    on a great deal of other information.

    when you have iron it rolls from whatever to where ever ...

    if you are unhappy today with the temp then maybe it is because it is colder out side if you are unhappy tomorrow maybe its warmer outside , if its 90 outside maybe you might not even want it turned on at all.

    for an example.

    This is an on going discussion that may help you wrap your mind around the subject a litle bit more .

  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    Radiator temp

    A cast iron radiator in a hot water system should only be as warm as necessary to meet the heating load at a given outdoor temperature. Since this type of radiator has a high thermal mass, it takes a long time to heat up but then it continues to give off heat long after the boiler has stopped firing.

    If the system is maintaining a constant indoor temperature at the thermostat setpoint, then the radiators are as warm as they need to be.

    On a mild winter day, an 80 degree radiator temperature would not be unusual. I think you will find as the outdoor temperature gets colder, the radiator temperature will increase as necessary to maintain the indoor temperature at the thermostat setting.
  • derbyct
    derbyct Member Posts: 4
    Cranked up

    I understand it will heat up as necessary. But if I have it cranked up so boiler is forced to be constantly on, what would you expect the temp measured at the radiator to be? Well over 100 Im guessing since anything below is same as human body temp which hardly heats the room.
  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    Max tmp

    Usually, systems are designed for a max water temp of 140 to 180 degrees. So on the coldest day the system was designed for (design temperature) the radiators might approach those max temperatures, but typically under normal conditions it will be much less.
  • Paul48
    Paul48 Member Posts: 4,469
    edited November 2013

    Have you bled all the radiators? With the cold we've had here in CT ( West Haven),your radiators should be getting hot. With my 90 yr old colonial, the thermostat placement is not very good anymore. There have been additions put on the house that now change the heat loss for the area. If you're having trouble getting the heat to the rooms farthest from the thermostat, try shutting off the valve to the radiator in the room with the thermostat. Oh....and thermostats behind and over a TV will really screw up the comfort in the rest of the house.The TV will keep that thermostat at around 72 degrees, while the rest of the house gets down to about 60. Just a thought.
  • Weezbo
    Weezbo Member Posts: 6,232
    edited November 2013
    Paul , Habby ThanksGiving.


    that is an excellent point , twice i recall having very odd calls about radiant not working.

    Once i arrived to see , a toaster , was placed under a thermostat who would dream that could ever occur?

    Another time , one of those oil filled electric radiators cranked up on high sitting directly beneath the Tstat .

    : )

    the TV idea reminds me of like a bank of battery chargers and various transformers that crank out heat for computers ,

    that TV idea is somewhat like the lady who was having a cold "Hot",water problem., she had hung a picture of her granny or something over the hrv controller because it was flashing all the time ... lol the block of ice i found inside the hrv explained what was going on .


    some very fancy outdoor reset programs can be given some different design info to make them work better for comfort , this may stir up some debate buh here goes ,

    instead of design degree day being 30 below try - 10 instead , it will still do all the fancy stuff it will just arrive at what you told it to a little quicker , it is backward thinking

    that for maximum eff, however it should respond a little sooner for heat that way ...

    the TRV acts like a bypass right there at the rad so the boiler is "moved" from the basement to each individual radiator, that speeds up delivery also ,

    adding in some aluminium conduction plates on those pex runs to and from the radiators can provide some added ; floor , wall , beam, post , ceiling heat . i have added short sections of baseboard too,.. that seems to change the complexion of a room . while not exactly bumping the iron radiators up those are some ideas... that one or two may come in handy on the comfort side of the deal .

This discussion has been closed.