radiator mystery

Kevin Blair

This is a one pipe steam system.

I have written about it before, but here are the basics and the problem:

This is a 2 unit building with separate 1 pipe systems for each unit. The lower system is in perfect working order.

Both boilers are newer and working fine and were cleaned about 1 year ago.

There are three radiators in the attic, which is finished. 2 of the 3 come on w/o problem and work fine.

In fact every radiator in the house, except one comes on and works fine.

So the mystery: what is up with this one radiator?

Vents: all vents are new and I am trying my 3rd brand new vent on this radiator.

Radiator: All seems fine. I have used a compressor to blow air through the radiator and it seems fine.

Valve: I have removed the valve and cannot see anything wrong with it. It is open and there is no sign that it leaks and it clearly isn't blocked.

pipes: I removed and replaced some piping from the valve to the first elbow in the attic (see picture) and some in the basement at a union (see picture). The piping I removed seemed fine; no sign of any blockage, but I figured I needed to at least see what is up with the pipes. I have blown air through the pipes from the value in the attic to the pipe opening in the basement where I had removed the union w/o problem. I have also poured water from the valve (about 10 oz) and observed it draining from the open pipe at the union in the basement.

So it doesn't appear to be anything with the pipes.

If you look at the picture of the new pipe and union: to the right of the union the pipe is hot, to the left it is barely warm and at the first elbow it goes cold.

So, it appears that only air can be blocking the steam, but if it is air, how is the blockage occurring?

I have to be missing something here, but what? all ideas appreciated!

Phil_17

I'll hazard a guess

That union you show is attached to a Tee which looks like it comes from a main and then goes on to feed other radiators, right?

If the other radiators (fed from the straight-thru shot on that Tee) are well vented (which I think you said is the case) then the momentum of the moving steam will tend to carry it straight across the Tee and into those radiators. It takes energy (aka pressure drop) to make the steam turn a corner and there is none available. To paraphrase Dan, flow always moves to low pressure.

You need to find a way to slow the steam down in order to get it to turn. You can try an experiment with closing off one or more of the other radiators that are being fed from that Tee, and if that gets you heat you might then try using smaller or adjustable vents on those rad's to get more of a balance amongst them.

In a perfect world, you would probably be better off with the feed for the cold radiator coming out of it's own branch on the main, but that's going to be a lot of work to re-pipe...

Unknown

sizing

Measure how many square feet of radiator that pipe is trying to supply, and multiply by 1.33 to get the load on that branch. Check sizing tables to see what size pipe is required for that amount of load.

As was said above, since that branch isn't directly connected to the main, the other radiators will need to fill, close their vents, and cause back pressure enough to redirect the steam (which is flying along at over 30 mph) into your new branch. What steam makes the turn will have to overcome the huge amount of returning condensate from uninsulated piping.

Steam pressure isn't like air pressure, in that it isn't constant along the pipe run,it tapers off as the temperature drops off. In order for more steam to fill the branches, there has to be room for it all, including what collapses and turns to water.

Noel