Dunham Vapor System Piping

Brirob

Hi All - having a bit of an issue with a few rads on my vapor system and hoping someone can give me some pointers. This is a Dunham Vapor System installed in 1926. The system was originally coal, converted to oil, and converted to gas ~25 years back.

For some background, when we bought the house last year, the 25 year old WM EG-75 near boiler piping was all wrong (included a pic) and after first fire I noticed some moisture on the ground. Pulled the cover and found a nickel sized hole in the top of one of the sections. The wet returns were also completely blocked so not sure how any condensate was making it back to the boiler. The system had seen no maintenance in years. So I bought new a properly sized Crown Bermuda and took the opportunity to redo all the near boiler piping, get the venting sorted out, replace steam traps, install a vapor stat, a low range pressure gauge, and crossover traps. There's about 810ish sf EDR of radiation and the WM boiler was rated for 733sf. The boiler is rated at 833sf steam.

The original part of the system (15 of the 18 rads) that is all fed by 2 mains -one 3" takeoff from the header and one 2.5" branch- are working great. The three rads fed by the second 2.5" main are a bit wonky. This part of the house was hacked up a bit during a kitchen reno some years back. It's a bit hard to describe the piping config but that main runs from the header into a tee. On one side of the tee, before any of the risers, another 2.5" pipe runs back and down to the wet return and there's no crossover trap...weird. On the other side of the tee, the main continues on and feeds the rads for a second floor bathroom and a second floor bedroom before deadending into a 90deg elbow which feeds the kitchen rad on the first floor. The first rad (second floor bathroom) gets barely any steam. The top of the first few sections get a little warm. New steam traps so I don't think it's a venting issue. The other two rads get hot eventually but much slower than any of the rads fed off the other mains. 

Kind of hard to describe so I linked a video of the layout. I'm thinking air is getting stuck in the main and that's what's causing the issue. I think my best option is to cut out the dead ended portion of the main and route it back to that wet return drop and put a crossover trap there. Thoughts?

https://youtu.be/RYzFV4hivPk

Jamie Hall

A deadended main -- with no return, perhaps? -- on a vapour system just isn't going to work. As you have found out.

Is there a dry return associated with that main? The radiators should empty, through traps, into that dry return. The end of the main should have a crossover trap into that dry return. Then, on the dry return somewhere handy there has to be a good sized vent. Then the dry return can drop into a wet return as a drip.

Is that even vaguely what you have?

Brirob

Thanks for the response. That's exactly the system I have - on two of the mains. The mains drop into the wet return with a crossover trap on each going to the dry return. Dry returns vent before dropping down to the wet returns. On the third main, this is not the case. That main runs into a tee. On one side of the tee, it pitches back towards the boiler and drops into the wet return - no crossover trap to the dry return. On the other side of the tee, it runs a few feet and has the risers for the three problem rads. It deadends at the last riser. It also pitches back towards the drop to the wet return so condensate does make it back to the boiler. The problem is that it relies on the radiator steam traps for venting the main. I think this is why these rads are heating so slow. Never seen piping config like this.

pedmec

What I like to do when i get issues with the piping is i put it down all on paper. It helps to be able to see the whole system at once. Clears out all the clutter. While the video is great i really couldn't keep up. By putting it on paper you can simplify the layout. Just the layout of the basement and the location of the radiators that are not getting hot. Post the sketch and you will get better info to help you.

Steamhead

Sounds like whoever the remodeler used for piping work- probably the low bidder- doesn't know Vapor. This is a common problem with remodelers. Any chance of recovering the cost for repairing it?

Brirob

Good idea. I'll sketch it up today and post.

Jamie Hall

This can be recovered, but balancing is going to be really tricky. That one problem main is piped like a one pipe steam system, and will have to be treated like one. To make it more interesting, one pipe systems usually run on slighty higher pressures than you want for the rest of the system.

What is going to be needed is a really big main vent -- maybe two or three Gorton #2s -- on the dead end. Make sure all the pipe pitches are correct for one pipe; if they are counterflow (steam going back to the in the main) the pitch needs to be steeper. The steam main extension (where it loops back without any crossover) needs to drop to a wet return before it joins anything else.

Then -- you will need to vent those three problem radiators very agressively. Also -- just thought of this -- they must be installed as one pipe radiators, with the steam inlet at the BOTTOM of the radiator (the vents a third of the way up at the opposite end).

Brirob

Thanks Jamie. I may be overthinking this a bit. What would be the downside of just adding a crossover trap to the dry return that runs just above this main and venting the end of the main to the crossover>dry return? Condensation already flows back towards the wet return in the opposite direction. So with this method, air has a path back to the dry return vents at the boiler and condensate has a path back to the wet return.

I'll get this sketched up and posted this evening.

Jamie Hall

Brirob said:

Thanks Jamie. I may be overthinking this a bit. What would be the downside of just adding a crossover trap to the dry return that runs just above this main and venting the end of the main to the crossover>dry return? Condensation already flows back towards the wet return in the opposite direction. So with this method, air has a path back to the dry return vents at the boiler and condensate has a path back to the wet return.

I'll get this sketched up and posted this evening.

That will work, provided those problem radiators have a return connection. It's not clear whether they do.

Brirob

Yes, apologies, I wasn't clear about that. These problem rads do have return connections to that dry return I mentioned. I think that's the only reason those problem rads were heating at all. The main was venting air (somewhat anyway) via the rad traps. I have a spare trap and fittings laying around so I'll cut into this week and give it a try. 

On the dry return venting - I'm wondering if there's any real benefit to running this system in a vacuum as it was intended back in the coal days. It had a Hoffman 76 on it when I bought the place but I removed it and added a couple of B&J big mouths for faster venting. I guess I could run a flap check in the horizontal pipe just before the big mouths and get the same effect as the old Hoffman. System runs at a max of about 4oz on longer burns. Usually < 1oz on shorter burns.

Jamie Hall

No advantage, really, to the vacuum. It was wonderful with coal, which died down and gave up some heat for a long time -- but modern burners are either on or off