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Best way to increase output from 8-fin cast iron steam radiator converted to hot water

chasepgt Member Posts: 6
Hi, so I'm debating with my contractor about how best to proceed on a project involving a bedroom we are revamping.

The major issue at hand is how to improve the output of a 8-fin (not sure if that's a real term, it's a radiator with 8 loops on it?, about 20" wide, 10" deep, 45" high roughly.

The room is small, and is very cold in the winter. Contributing factors we are addressing:

* Lack of insulation under a bay window

* no insulation above in the ceiling or attic

* removing a shelf 1 inch above the existing radiator blocking air flow

* insulating a closet that is facing an exterior wall that had no insulation behind it previously

The radiator itself (besides the shelf above it) also suffers from 2 issues.

1. It's copper supply and return line pass through an exterior wall that has some sparsely settled cellulose insulaation blown in.

2. These copper supply lines are fed by pex supply lines that are fed in a loop from another radiator in another bedroom.

My question from you is this... If you had to break down by percent (best guess) what the contributing factor is for this radiator to not be getting hot enough to heat the room...

Which of the two issues I cited above should I address first? IE, is it 50% due to the radiator being second in a loop? and 50% due to the supply lines for the radiator being in an uninsulated exterior wall?

Our plan is to relocate the radiator to a position where we can run new supply and return lines through an interior wall.


Add a dedicated supply and return line from the boiler manifold for the radiator.

Ideally we do one or the other (due to cost) not both. I get that ideally I should do both, and eventually we probably will but which should I do first?


  • chasepgt
    chasepgt Member Posts: 6
    another note

    Note that the supply/return lines in teh exterior wall have never frozen and this has been plumbed this way for a long time.

    The previous owners just left the bedroom door open and allowed heat from the rest of hteo house circulate into the room.

    We plan on using this room as a nursery and want to be able to close the door so that our older kid doesn't wake the baby when napping, etc.
  • icesailor
    icesailor Member Posts: 7,265
    edited March 2014
    Right & Wrong:

    If there are two radiators in in any or different rooms, and there is a single supply and return for the two radiators, it is wrong. They both must have their own separate supplies and returns. Especially if the bedroom radiator is the second radiator on the series loop. Does the other radiator get hot before the bedroom radiator?

    Unless the radiator is grossly undersized, from what you describe, the radiator should be able to heat the room. If you can get at the copper pipes where the PEX is located, change the PEX to 3/4" and make the room a zone of its own and you can control the room temperature with its own thermostat with the door closed. All you would be doing is correcting some mistakes in the piping.

    A couple of zone valves and you should be in fine shape.

    The shelf above the radiator should not be  serious hindrance.

    As far as the radiator, post how high off the floor it is, how many tubes in a section and how many sections are in the radiator. Post a photo too, if you can. We can tell you the output of the radiator. It isn't the width (10"), it's how many tubes there are in the 10" wide section and the height.
  • SWEI
    SWEI Member Posts: 7,356
    Measure first

    Buy a few clip-on pipe thermometers.  Install them next to each other on the same pipe to verify that they read consistently.  If not, take note of which is off by how much so you can make reasonable measurements with them.  Now move them so you can see the water temps at the inlets and outlets of both radiators.

    Re-piping the two radiators in parallel rather than series will help a lot.  How much will be determined by the measurements above and the size of the pipes feeding them.
  • chasepgt
    chasepgt Member Posts: 6
    edited March 2014
    pics of the radiator

    Well, I don't know how to put a thermometer on the pipe to test but can say that the first radiator in the series gets so hot you can barely hold a a hand on it where as the second one (pictured) gets just a bit warm to the touch.

    I am positive that it is the second radiator in the loop because the loop is visible in the basement. the supply line crosses across the basement ceiling, then up a wall into the second floor first bedroom. It then comes back all the way down into the basement, crosses the basement, and then up the exterior wall I mentioned and into the radiator in the second bedroom on the second floor. The loop in the basement is 3/4 pex but the pipes in the wall are copper.