Cast Iron Radiator Copper Feed

[Dennis6969]

Hi looking for a little help with plumbing my cast iron rads. I have 2 cast iron rads that are free standing 9” wide, 22” tall and 25 sections. From any data I can see each works out to 75 sq ft, at approx 170 degrees for water temp each will push 11,250 BTUs. I plan on doing a home run system, manifold piped to individual rads. I am going to do it out of Copper (my preference) starting from a Grundflos 15-58 3 speed pump to an 1 1/4” manifold with outlets. I’ll have shut off on the supply side and balance valves on the return. My question is I’m in the air about using 1/2” or 3/4” copper for the runs. The runs are about 50’ of pipe. I know 1/2” is good for 15000 btu but I’m not sure if the volume is there for rads of this size. I don’t want to starve them of hot water flow and take longer to heat up. Also I am working with an existing system so don’t want to reinvent too much. Thanks in advance

 

[John Gayewski]

Use 3/4. It'll be easier on the system.

Are you using a pre-made manifold?

Generally nowadays people use pex to run to and from the boiler and the near boiler piping is copper. I would probably use pex for most of the piping and definitely use 3/4.

 

[Sponsor]

 

[Dennis6969]

Use 3/4. It'll be easier on the system.

Are you using a pre-made manifold?

Generally nowadays people use pex to run to and from the boiler and the near boiler piping is copper. I would probably use pex for most of the piping and definitely use 3/4.

Either a pre made Manifold or I may just make one. I don’t mind using pex but my preference is copper. It’s not that difficult of a run. I enjoy sweating pipes for some crazy reason.

 

[Sylvan]

I strictly use copper never smaller than 3/4 Type L.

Also make sure the FPS does not exceed 5 FPS and allow for the coefficient of expansion per degree with expansion joints

 

[Fitter30]

3/4" copper tubing 110° rise in temp 1.3" per 100' expansion.