Single pipe steam but one rad has a return piped back, purpose?

zooba

The house is single pipe steam, but I am trying to understand why my system has one radiator with a return piped down. I've checked other parts of the piping and it seems 95% correct, with a few errors like some risers joining the main at 90 degrees.

The system is structured as follows: mains split right after the header. Loop 1 services the old part of the house, being a properly sloped loop with risers coming off serving 5 rads. There is a single main vent at the end of the dry return. Loop 2 services the new part of the house, 8 rads, with a separate dry return with its own main vent that only joins the other loop just before going wet, right at the boiler. Part 3, not Loop 3, goes off and services 1 rad just above the boiler and two rads on the second floor. It is pitched back towards the boiler, no return, not a loop. It is one pipe there and back EXCEPT for a return pipe from the first rad that joins Loop 2 just before the boiler. So that one rad can return properly while the other two rads drip back into the header.

Photos of the returns and the rad in question.






House is 1902, addition 1940s(?), boiler is 2019, I bought the house in 2023. It's my first season. I'm trying to learn as much as I can, mainly through the web and I got The Lost Art (Revisited). The system was in horrible shape. The whole house was cold because the rad nearest the thermostat had a leak at the inlet valve acting like a permanently open vent. Other rads had no vent and the steam blowing out destroyed part of the wall and baseboard. Now it is an ok shape to get us through, but there are a lot of problems to get it working like it should.

EBEBRATT-Ed

If the piping is quiet and no water hammer and everything heats that is the goal. Sounds like they made some changes and additions which don't always go well. Not unusual. Sounds like you have 3 rads (part3) that are hooked up counterflow. The rad in the picture I would suspect is a "two pipe air vent system" (very Old"). You mentioned some rads return counterflow into the header that isn't the best situation. Maybe next summer you can cut a tee in that pipe and drip that pipe back into the boiler return connection.

Steamhead

That's a beautiful radiator. Maybe it banged and they figured the steam line was too small for the water to flow back.

Those return lines need to all drop below the boiler's waterline before tying together. Otherwise steam can jump from one to another, messing up steam distribution.

Those main vents are almost certainly too small. How long are the mains and what pipe size?

Where are you located?

zooba

Yeah, the system mostly works, some rads don't get fully hot so I'm trying to optimize at this point. Only one rad of 16 bangs and only on colder nights, I think I just have to tilt it properly. You're right, I don't want to make changes and make it worse!

I'm thinking now the one rad with its own return does two things:
1. That rad will continue heating forever even if its vent is closed
2. That return pipe may raise the pressure in the pipes at the very end of the return, messing up the other two loops. Going header to one rad to return means less of a pressure drop than the longer loops, and so the longer loops see a smaller pressure differential, making them heat slow.

1 means I should really be removing that return line.

2 means even if I fix the leaking inlet valve, the rad will still overheat and mess up the whole system since its the primary rad for the thermostat.

Thanks for the tip on searching up "two pipe air vent system," it helped me to understand how the flow and return should work.

Main loop 1 is about 50 feet of 3" pipe and then 2.5" pipe for the last 15 feet.
Main loop 2 is 32 feet of 2.5" pipe, then 10 feet of 2" pipe, then 25 feet of 1.5" pipe.
The counterflow line, Part 3, is about 16 feet long, 3" pipe.

I tried to estimate the EDR using the guides (like column or tube type, number of tubes, height, number of fins). I got
Main loop 1, 300 EDR
Main loop 2, 200 EDR
Counterflow (3rd mains), 80 EDR

Steamhead

Start with one Gorton #2 vent on each main, and add more if needed.

If the return from that one radiator is piped below the boiler's waterline, steam will not be able to get into it.

zooba

Thank you for the advice. I am going to wait until after this heating season and do the recommended work:

• Add one more main vent to each loop
  
• Change the counterflow line to be a proper loop. Should be easy since it is a straight line along the northeast side of the house.
  
• Make all returns join below the water line. Right now they all join above the water line.