Supply line size for cast iron radiator

Mariusz

Hello, I am moving some of the supply and return lines in my hot water cast iron radiator system and I wanted to ask if I can replace my current galvanized 1 inch pipe with 3/4 copper without affecting the performance I would insulate to copper pipe to minimize heat loss

ChrisJ

A bit difficult to answer that question without knowing what size the radiator is. How long will the piping be?

Can you share some pictures of the radiator, it's current piping and the boiler?

Steamhead

If this radiator is in an old house, given that pipe size this is probably a system that originally ran on gravity circulation. If that's the case, the answer is NO. You will not get enough circulation with a reduced pipe size.

This is a common mistake. AFAIK it comes from replacing water-supply piping, where galvanized pipe gets partially obstructed from all the fresh water it handles. In a heating system, the water is recirculated, so all the corrosive materials are used up quickly and the pipes stay clear.

Do not reduce the pipe size.

Steamhead

Not if this was originally a gravity system. If it was, and you reduce the pipe size to one radiator (thereby increasing its resistance) the water will simply flow to the other rads, avoiding that higher resistance to flow where the pipe size was reduced.

The OP says he is changing "some" of these pipes, not "all" of them. Unless the entire system is being repiped, reducing pipe sizes on just one part of the system will cause uneven heating.

Steamhead

Hatterasguy said:

1" can easily supply 140K BTUH to CI rads, so, hopefully you have a giant house or you live in Alaska.

We all know that depends on the water temperature. Again, the question whether this was originally a gravity system is everything. If so, it is likely running at much lower temperatures than a newer system, so a 1" pipe in such a system delivers much less than 140K BTUH.

Gordy

My questions are what was galvanized pipe doing in the system if the system was originally gravity?

Moving some pipes entails what?

Size of Radiator?

Your both right. One way keeps original system dynamics. The other requires rebalancing of possibly all rads depending on piping details to insure proper flow to modified rad.


Balancing the system is not all that hard if the OP has an understanding of how to accomplish this. Once done there is no more tinkering.

Solid_Fuel_Man

There is no simple answer, there is not enough information given in the OP to answer.

I piped several CI rads in 1/2 copper reverse return and they perform wonderfully well.... All about BTUs needed, water temps, flow rated etc etc etc....

SFM

Bry_2

I have the same issue but am willing to repipe all the gravity black pipe with 1/2" pex and tie into the rads with unions/fittings . Would that supply enough flow to heat the CI rads? I will cut down all the black pipe and fix the pex to the ceiling to give me extra headroom. Thanks.

Bry_2

Can rebalancing be done with a manifold and valves to even out the flow rates?