Adding radiators for a second zone on first floor

ivanator2

I had a Unico System install, including hot water coil and a new boiler. It was all undersized. Contractor installed a Slant Fin 140K Finally got contractor to perform load calc and after much back and forth, he agrees it's too small.



He's agreed to install larger boiler and I pay cost difference. He also agreed to put in a second zone, which would be piping to connect radiators on the first floor. I find and buy the radiators.



I will try and match the BTU output of the old radiators. There were six on the first floor. Each had an EDR of about 12,500.



I need to make sure the piping is done right. Should it be 3/4 " to a supply manifold and 1/2 " pex supplies to the radiators, and 1/2 " returns to a return manifold, then 3/4 " back to boiler?



This would be a separate zone with zone valves and a separate thermostat.

furnacefigher15

12,500 edr?

12,500 edr at 180 supply water = 21,250,000 btu



do you mean 12,500 btu each?



If 12,500 btu, then 1/2 inch ID pipe to each is fine. I would run 1 inch ID to the manifold. 3/4 is right on the cusp.

Paul48

heat loss

Do the heat loss for each room and size the radiators accordingly. It's easier to do it right the first time.