Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Pipe sizes for radiator panel heating

nickmg555nickmg555 Posts: 4Member
Good morning everyone,

I’m currently renovating one of my units in a 4 unit building and would like to slowly begin the process of switching to a centralized heating system. It’s a 1920 building and each unit is overall roughly 24x28 while the sub level unit is a bit smaller to allow for a utility room which the new heater will be housed. I have all the tools needed to do the plumbing but can’t get any definitive answers on pipe sizes. The system will be a high efficiency condensing unit running at 140 degrees to 4 panels in each unit with a thermostat controlled valve for each unit. I understand most of you will just say to hire the proper contractor but I’m not installing the entire system now just the sections that I can while I have the ceiling open for renovation in one of the units. My thoughts were to run 1” pex from a main that runs the 3 levels and then branch off with either 3/4 or 1/2 to each radiator and back to another 1” return to the main return. The feed and return pipes that run up through the building I would like to use the iron pipe but not sure if what size to feed the building. I would assume at least 1 1/4 if not more. I’m not hooking up any gas or electric or anything dangerous simply doing some plumbing here to get it ready as I renovate units. Any input on pipe sizes would be greatly appreciated


  • IronmanIronman Posts: 5,107Member
    edited May 4
    Pipe sizes are determined by the btus required.

    Generally speaking, here's a chart:

    Stay in the middle, between minimum and maximum. Which means:

    1/2" = 2 gpm
    3/4" = 4 gpm
    1" = 8 gpm

    You need to FIRST do a scientific heat loss calculation to determine what size equipment, radiators, piping and pumps are needed.

    SlantFin has a free app that you can download. Disregard any quick, square footage calculators that you may find. They're worthless.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!