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Sizing Cast iron radiators: Question

Ted_9 Member Posts: 1,718
I'm sizing a house for a customer that wants a modern boiler. They have cast iron Radiators on the first floor, monoflo. House was built in the 50's we beleive. Now he says the house has been cool since he bought it 4 years ago.

I'd like to do the heatloss and size the radiators to make sure that they are not under sized. This is what he beleives. To his credit, i did find one room that someone removed one of two radiators.

Anyway i measure and sized the rads and Ive got my sq foot of radiation for each rad. Now what do I do with that? Am i expected to use that number and the sq feet of the rooms? Doesnt make sense since each house has a differant loss. I just figured out one room and its already half of whats needed.

Any guidence here would be great. And I did get the radiator info from the Library on this site.



  • Victor H Plank
    Victor H Plank Member Posts: 17
    Radiator Sizing


    Square Foot EDR needs to be multiplied x 180 btus/hr for hot water
    or by 240 btus/hr for steam
    or divide your room by room heat loss by 180 or 240 to get EDR required

    Hope that is the question you are asking...dont forget about piping losses

  • Mike Kraft_2
    Mike Kraft_2 Member Posts: 398
    Entering water temp

    You should use 170° for your multiplier.This will be the average temperature through the circut.180° will be the temerature entering the first rad.You do need to figure your drop through the loop.Also make sure that the monoflow tees are removed from the loop where the radiators were installed.Or at the very least tie them together.

  • Ted_9
    Ted_9 Member Posts: 1,718
    Sizing Cast iron radiators: Question

    OH Mike thats it. That why that side of the house feels cool. The owner said that the rads were cooler there. The monoflo tees are just pluged.

    Ill work on those calcs tonight.
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