Loop not heating, possible solutions?

jsavage

Our system is one-pipe steam. For our kitchen there was originally a ducted connection to our indirect gravity radiators that was removed. In its place a set of fin tube radiators was installed in the crawl space under the kitchen floor. I tried to depict the layout in the attached drawing. 

This system has never worked for me, and I don’t think it’s worked since it was installed at least 50 yrs ago. It originally had a single vent. When I bought the house, I added a second vent and a check valve when I was venting all of the steam mains. I had the check valve lying around and figured I’d give it a shot. 

I think the steam is coming the wrong way through the check valve, closing the vent, and binding air in the loop. My thought is that replacing the check valve with a loop seal will fix the problem. Is that the best solution? Alternatively, is there a trap that would work? The main is only about 5” above the dry return.

Obviously if there’s something I can just replace the check valve with that would be perfect. I’d need to move some things around to put in a loop seal.

Thoughts?

Jamie Hall

Is that a real dry return, and is it thoroughly vented? If so, lose the check valve. Replace it with a loop seal — if you can get enough depth. Otherwise, you could install a regular trap.

Now.

Your drawing shows a pipe connection from the steam main to the dry return? Say what? If that's for real, then that's not a dry return, but a steam main extension It will have the same pressure in it as the main, and there is no reason for steam to ever get into the fin tubes at all, check valve or no check valve. You might get away with placing a vent on each fin tube at the far end away from the steam connection — provided the fin tube is pitched back to the connection so condensate can drain. On the other hand (and the drawing is not clear to me) if the fin tubes are in series… your only hope is going to be the vent you show between the fin tubes and the check valve, and then a true wet or dry return from there back to the boiler to carry the condensate.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1817492#Comment_1817492

@Jamie Hall would it work with a water seal or a steam trap both at the end of the fin tube and between the main and the return?

There will never be enough pressure in the weight of the water to open the check valve so that will never work. It has to be a water seal that works on the weight of the water or a steam trap that works on the temp of the steam.

The fin tube will never heat the same as the cast iron radiators so having them on the same zone won't work so well. It might make a whole lot more sense to make the fin tube a separate zone off of the condensate in the boiler.

Jamie Hall

Indeed it would, @mattmia2 . And probably not all that hard to do — there are lots of systems out there with an independent hot water zone off a steam boiler. Not off the condensate — there's not enough heat there to make tea — but a pumped loop off the boiler.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1817516#Comment_1817516

I meant the water in the boiler, not the condensate line. Maybe that isn't the right term.

jsavage

@Jamie Hall You are right that the pressure inside the return is the same as in the main. It’s a one pipe system so there is no isolation between the returns and the mains, the return just provides a return pathway for the condensate so it’s not flowing back against the steam.

@mattmia2 the solution of two traps seems to be the right one. My concern with adding one trap was that steam would be able to get to the return side of the trap, which (based on my limited understanding of two-pipe systems) could cause the trap to fail. But using two traps seems to avoid that issue by ensuring no steam gets into the return.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1817613#Comment_1817613

Fair enough. With that fin tube connected at both ends to the same pressure, it's never going to heat without a vent somewhere along the fin tube… and then only so far as the vent.

A so-called "dry return" which isn't strikes again…