Two Pipe radiator plumbed in after the vent on the return

Ted_Ryan

Quick question. Added a new radiator and the return for this radiator connects to the main past the location of the main vent. This return is a wet return if that matters. Should this be corrected or does it not matter. The return run plumbs in about 6 inches past the main vent. Thanks for any input.

Jamie Hall

The return is plumbed to a wet return? No vent? How does the air get out of the radiator?

However, a question: there is no need for a vent on a wet return. Are you saying there is a main vent on a steam main? Depending on the piping, that is probably needed. But on a two pipe system, the returns from the radiators must go into a DRY return, which is vented.

So... what have we here?

EdTheHeaterMan

Let me take a wild guess. That one radiator is not heating as you think it should.

A few pictures or a diagram would be interesting.

Mad Dog_2

Pictures AND diagram. MAD DOG 🐕 

mattmia2

Is the rest of the system 2 pipe? Is there a vent on the radiator?

Ted_Ryan

Thank you very much for the clarifying questions. The system is a two pipe trane vapor system. There are two legs of return mains. The return main in question is a dry return until the very end where due to access and pitch issues, the return drops down to the basement floor for the last 15 feet or so and travels below the boiler water level. The vent for this main is located in the dry portion. Jstar did the work in 2013. The radiator was added afterwards by another contractor.

The return run from the new radiator ties into the return main near the end just before it drops down to the basement floor becoming a wet return. Again, the vent is in the dry portion of the return and the last radiator ties in just after the main vent, but before it becomes a wet return. The radiator heats well, but I am getting some short cycling (Vaporstat cut out) after steaming for a while, and wondered about whether this radiator plumbed after the vent might be messing with the overall venting of this main. In my mind I imagine venting air from all the other radiators running toward the vent from one side and then this one radiator is trying to sneak in from the other side. I run at around 8 ounces. I can try to get a photo if necessary, but it will be tomorrow because it will involve some crawl space crawling!

mattmia2

Do you have a vapor valve or orifice plate or steam trap on the new radiator? Do all of the radiators heat adequately? If anything another radiator would lengthen the cycles. The air doesn't care which way it flows to the vent as long as the path to the vent remains above the water line.

Jamie Hall

If it's working, I'd not worry about it, but...

I'd be mightily surprised if those pipes to which you are referring as "return mains" are actually steam mains. It is far more likely that they are dry returns (no steam, just air and water)

Which leads me to the next obvious question: how are the actual steam mains vented? They either should have main vents at the far end (away from the boiler) or they should have crossover traps (and, possibly, water seals) to the dry returns. Either arrangement will adequately vent the actual steam mains -- but one or the other has to be there. If there isn't that, adding one or the other might help with the cycling -- and will certainly help getting all the radiators hot quickly and evenly.

Ted_Ryan

The radiator has a trap on the return side. As long as there is not significance to the direction of the venting air flow, I think I need to look in another "direction". Regarding the entire setup, the radiators all heat. I leave the thermostat set back at 1.5% before it trips so there is plenty of time for all the radiators to heat before the thermostat is satisfied. Thank you very much for the input. Ted

mattmia2

What @Jamie Hall is getting at is if the mains have to vent through the radiators instead of having their own vents they may build pressure before they completely fill with steam.

Ted_Ryan

I was sloppy in my language. All of the piping I am referring to are dry returns....carrying condensate and air. All of the radiators have their own supply valves (about 1/3 with TRV's) and all with their own traps on the return side (about 2/3rds with traps replaced in 2013).

Appreciate all the input! Ted.

EBEBRATT-Ed

@Ted_Ryan

If it works ok and it likely will there is no need to relocate the vent. If you have a problem just stick a vent on the radiator return close to where it ties into the main return.