Cast Iron Radiator Piping

denn6969

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 am going to have more than 2 outlets for future connections. I’ll have shut offs 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. Would 1/2” copper work well? Also I am working with an existing system so don’t want to reinvent too much. Thanks in advance

Ironman

Are there other rads and existing piping that will remain in the system?

EdTheHeaterMan

1.5 GPM will move 15,000 BTUh when there is a 20° temperature difference. So, 1/2" copper to the radiator will work just fine. What may be confusing to some is that old gravity flow systems needed oversized piping because the did not include circulator pumps. so that radiator (if found in a old radiator recycler) might have 3/4" or 1" pipe openings since it came from a gravity system. When you have a pump involved that is when that 1/2" = 15,000 BTUh rule applies.

EdTheHeaterMan

Are you going to use the same pump for the new radiator manifold as the circulator pump for the remainder of the system?

That may cause a balancing problem. Since the old gravity system has large pipes, that is the path of least resistance for that pump, and therefore tho old system will get more BTUs flowing there and less to the more restrictive radiator piping.

If however the new manifold gets the boiler water fed by a separate pump (separate zone) than there is no problem.

denn6969

so I have 3 zones all fed by separate pumps controlled by a taco zone panel from a 1 1/4” iron pipe manifold off the boiler. This is only one zone. My other zone is cast iron baseboard fed by 3/4 copper in a series loop and the last one is slant fin 3/4” pex fed series loop. I know most say series loop with cast iron is taboo but my base board is Baseray and they actually recommend it for the baseboard. I refuse to do it with these monsters though which is why I want to do home run piping. My Rads do have a 1” bushing in them that I don’t care to try and remove so for aesthetics I may keep it 1” brass for the above floor portion and reduce it just below the floor. Also this is a first floor, the piping is rising maybe 2’ max.

EdTheHeaterMan

Good to know that you have a handle on the zoning situation. You dont know how many times I have arrived as a home that has Cast Iron standing radiators with a copper/fin baseboard in the location of an old CI that was removed. And the folks don't know why that room is so cold…

You sound like you have your 💩 together. Good luck with your project.

Aesthetically, the 1" valve might look good then reduce under the floor, but you can always have a Brass 1" x 1/2" bushing polished on the flat and hex sides to match the brass radiator valves and return bend unions.

denn6969

Glad I posted. Thank you for the help. I really appreciate it.

mattmia2

You could also just paint the piping the same color as the radiator. Black iron is fine for the piping functionally, it won't rust appreciably in the closed heating system.

EBEBRATT-Ed

If your connecting both rads to the same supply and return use 3/4" otherwise 1/2" should do it

denn6969

https://forum.heatinghelp.com/discussion/comment/1814681#Comment_1814681

can u explain this further. The manifold will be 1 1/4” with 1/2” outlets in both supply and return. With balance valves on the return side I should be able to get equal flow to each rad on the zone.