Sizing replacement cast iron radiators

bob eck

Good evening
How do you size a replacement cast iron radiator?
I was told to get the following info.
How many tubes.
How high.
Width.
Number of sections.
I needed to bid a job of radiators that froze and broke.
My rep told me just give him the demenitions from center to center of the supply and return pipe.

RJMCTAFO

Room by room heatloss. Then size the radiators from that. If you copy what is there you will most likely be over radiated.

STEAM DOCTOR

Are you replacing all of the radiators? If yes then first step is room by room heat loss.
If you are only replacing some radiators then it gets a bit tricky. There is a case to be made that you should replace old rads with new rads of similar BTU output. Idea is to keep all rooms balanced. You might be better off with all rads proportionately oversized rather than having some properly sized and some oversized. Of course, a heat loas and rad survey will give you precise info.