steam loop not heating up

charliechicago

Hello to all,
I have a customer that has a one pipe steam system that branches out into three main loops. The radiators on one of the loops do not heat properly. It takes a very long time for the heat to get to the radiators and they don't heat to the end. I noticed that the rads are "breathing/panting" they push air out and then suck it back in. Any suggestions?
Thanks, Charlie.

KC_Jones

Panting can be indicative of water laying in the mains, I would start with verifying the pitch of all the pipes as well as ensuring they are straight. A piece of string and a level are your friend here.

Next you need to look at the main venting those mains need to vent as quickly as possible and the rads need to vent slower for control. This isn’t only a question of having main vents it’s also how much there is.

charliechicago

Thanks for the response.
The pipes are pitched correctly and the main air vent seems to be working fine. Nothing has changed with the vents on the rads, but I could check to see how large they are. Wouldn’t water laying in the pipes cause hammer? I’m not getting any. Is it possible there’s a blockage? The pipes are not insulated, but they have been that way for a long time.
Thanks.

Fred

You say "The main air vent" Does that mean there is only one vent, in a single location? If so, each of those branches needs to be vented, after the last radiator run-out. It's not likely there is a blockage in a steam main. Nothing gets in there but steam. The fact that the mains are not insulated isn't helping. Steam could be condensing very quickly in those mains and that condensation can cause the panting. Also, the radiators don't need to heat all the way across, and usually don't unless there is a very long call for heat. The goal is that the thermostat reaches set point and the rooms are comfortable.

Turn the thermostat up 2 or 3 degrees so that the boiler runs longer and see if those radiators get hot. I'm guessing there is an issue with the main venting and a longer heat cycle will push the air out of the mains to get steam to those rads.

KC_Jones

charliechicago said:

Thanks for the response.

The pipes are pitched correctly and the main air vent seems to be working fine.

Thanks.

Again this isn't just about them working it's having the appropriate amount in all the correct locations. If there are 3 mains as you state then there should be 3 different main vent locations with the proper amount of main venting. If you have the pipe lengths and sizes we could recommend how much main venting would be needed.

charliechicago

Thanks again
Fred, each branch has its own main air vent by the boiler. I understand that the rad does not necessarily need to heat all the way across but the room is not warming up properly because the rad is not heating fast enough. When I put the t stat higher it will eventually heat all the way across, but during normal operation the room is cold. I could insulate the piping but I'm still not sure why it would start to have an issue now, the pipes have not had insulation for many years. Also, wouldn't too much condensation cause water hammer?
KC_Jones, are you saying the loop with the issue is venting too fast or too slow?
Thanks again, Charlie.

KC_Jones

The mains should vent such that none of the radiators get steam until the entire main is filled with steam, once that happens then the steam should move to all the radiators at about the same time so everything is even.

How long are the mains and how much venting is on them? If you post the length and pipe size we can recommend the amount of venting you should have.

It is my experience around here that mains are typically way under vented.

Fred

@charliechicago ,Have you tried to balance the radiators across the entire system? Don't limit yourself to the one main. It could be that the other rads are stealing all the steam because they are vented too aggressively.
If this is a new situation and nothing else has changed, Have you clocked the gas meter? It is very possible the boiler isn't firing at the correct rate. May be a gas supplier issue.

Also, be aware that excess condensation in the mains don't always cause hammer. There is some threshold where it will but on a one pipe system, there is always some level of condensation in the mains, headed for a wet return.