Pipe Sizing for hot water radiators

ExcuseMonster

I am currently doing home renovations and have acquired two new cast iron radiators to replace the existing baseboard hydronic radiators in my living room and dining room. I have sized them based on the marks left on the floor from prior. I will also be looking to replace a few of the isolation valves with thermostatic radiator valves (for the few in the bedrooms). With the new cast iron radiators installed I will have a total of 9 cast iron radiators (7 on the first floor, 2 on the second). The existing baseboard radiators appear to be on one zone, the cast iron on another. Based on the manufacturer catalog the total for all radiators add up to 282 EDR (approximately 50k BTU’s I think). The existing supply pipe is 2” steel. The 1” supply to baseboards is tapped off that. Then both with separate returns back into circulating pumps and back into the boiler. My question is, if I were to redo the supply and return pipe for the entire system (as I will already have to run new lines for the new cast iron radiators I’m adding), what size pipe would the supply (and branch lines) need to be as well as the return lines? I am just learning the system and operations so forgive me if my math is completely wrong and please help me make sense of this or if I am missing information. Would a 1” supply with 1/2” branch lines be sufficient for the entire system? I can provide a break down of all radiator sizes and rooms if needed.

EBEBRATT-Ed

From your description I can't quite make out what your doing. Can you post a sketch?

282 EDR would need 4.3 gpm which is with 170 average water temp. 180 supply 160 return and the GPM would be 4.3 gallons/min.

3/4" pipe or tubing would do this if the length of run and the fittings are not too excessive

Sizing radiators based on the marks on the floor is not the best method.

mattmia2

note that if your edr calculations are correct, that boiler produces about twice as much heat as your emitters can absorb.