2 pipe, short cycling, 1.2 psi

ProblemSolver

This is a classic! An upper seal on the original steam boiler was shot (the boiler is in a 3 car garage that heats a living quarters above it with 4 radiators, plus one 1-1/4 x 5 ft. fin/tube type baseboard in garage). A close friend who just semi-retired from this business sold this customer a new boiler and turned it over to me. After removing the old boiler, I felt uncomfortable to start assembling the new 125MBH / 90MBH Weil McLain Boiler. So I measured the connected radiation and came up with 40MBH. I changed out the new boiler for a Weil McLain 75MBH / 47MBH. After getting this new boiler connected and fired-up; I replaced the main steam vent because it would not close. Also, replaced a radiator vent in the garage baseboard. My main problem, after firing up the new boiler, was the radiator in the small bathroom wasn't heating, and this radiator is connected to the main steam line after the main vent, and before the vertical return drop. Also, the other 3 radiators would only heat at the top 4 inches of the radiators. Plus, the baseboard in the garage was banging and the vent was spitting. Now, I am at the part of the job where I can sit back and look at the system as a whole. Here's where it gets good. This 2 pipe system, with a wet return spanning from the farthest radiator & back to the boiler, has been operating, from conception, without air vents in the returns. There are 2 vertical return drops after the radiators; 1 is the bathroom radiator, and the other is connected to the other 3 radiators which all share a main return in the ceiling. And if this wasn't enough! The baseboard in the garage is mounted about 30" off the floor. It is connected to the steam main and the wet return. When the boiler fires-up, it raises the water level in the vertical return drops (Dimension A), and the baseboard is a part of one of those vertical return drops. It's not steam heating this baseboard, it's actually hot water heating it which is why it's vent was spitting. Now this part I really love: the side of the baseboard that is connected to the wet return is actually the supply side, and the side of the baseboard connected to the steam main is the return for this baseboard. When the boiler fires-up and fills the baseboard with water, the baseboard's pipe connected to the steam main, uses the steam main as it's vent. I will be plugging of the baseboard's vent opening; but for right now, I used an adjustable vent and I shut it off. This system has got to be over 75 years old and not one steam technician questioned its poor operation. Just in case you don't understand; the boiler got to 1.2psi within 2 minutes of making steam because the radiators could not bleed the air out (the return piping off the radiators was blocked by the wet returns / with no vents), so the steam would compress the air in the radiators, thus raising the pressure in the system and at the boiler - quickly. I am returning next week to install the vents in the radiator return drops / above dimension A, but about 8" below the return piping at the ceiling. I see no other way of getting return air vents in - plus the vent for the bathroom radiator, I will be using an adjustable verivalve radiator vent, and the vent for the other 3 radiators will be a Hoffman 4A - anyone with thoughts?

KC_Jones

I am a bit confused...if this is a true 2 pipe system, why are you putting any vents on the radiators at all? A true 2 pipe system shouldn't have any vents on the radiators, but should have steam traps on the outlet side of the radiator. The whole systems sounds weird, some pics of what you have would help dramatically.

Steamhead

I think he means he's installing the vents in the dry return. Certainly not the first time I've heard of this situation. The most recent one we encountered was where someone replaced a boiler, removed a Differential Loop and did not vent the dry returns. You can't fix stupid!

Jamie Hall

Oh but differential loops are so so scary!

SWEI

Is there anything fundamentally wrong with venting a dry return?

gcp13

I have an old system I work on,its a two pipe no traps with air vents on each radiator and vents on the returns for each return in the basement before they drop down to a wet return. At the boiler there is a false waterline to keep the return under water.
They are old bundy radiators with regular steam radiator valves on inlet and outlet,
No metering valves or return elbows like a vapor/vacuum system.
In the basement it a maze of 1/2 return lines along the ceiling,each radiator in the house 18 of them, has the return run by itself to the basement into the wet return.
After I replaced the boiler adding a drop header, two risers,added hose bib at the start of wet return so I can hook a hose to it and flush clean,setting the pressure as low as I could with a pressuretrol the system is quiet heats quick an all radiators heat great.

ProblemSolver

You got it Steamhead, on both accounts. The piping for this living space above the garage, use to be connected to the house boiler, and where the return drops (inside the house) there is the air vent for the returns. But then, someone disconnected this piping system in the garage, from the house system, and added a new boiler. Sorry about the confusion KC Jones. I knew this would mess some up. A steam traps only purpose is to keep steam away from condensation. A steam trap is not a vent, although you might assume it acts like one because it stays open until steam hits it. But the air cannot leave the radiator without a way to leave the piping on the return side - after the traps - all the traps. The return piping for 3 of the 4 radiators share a common return header located in the ceiling of this garage. That common return then runs to the corner behind the boiler and drops straight down to the wet return. There is absolutely no way air can leave the radiators or the return piping because it ties directly into a wet return.

ProblemSolver

I couldn't reply on this until now because I have been sick. What I really wanted to get some feed back on was about the baseboard in the garage. After some thought, I think it's best to completely disconnect it from the steam main and install a radiator vent on that side of the baseboard, keeping the vent as high as possible (at the ceiling). Any thoughts?

ProblemSolver

Hears a drawing of what is there now, I didn't label everything because to most it's obvious.

KC_Jones

I am guessing your idea is to get the vent above the water/Dimension A. In my mind though won't that baseboard still be completely filled with water? It just doesn't seem like moving the vent will do a whole lot if everything is filled with water. Basically all you end up with is a hot water baseboard heater with inadequate flow...maybe that's how it should be thought of? Do you think this is original or someones homegrown effort to get heat in the garage?

gcp13

Sorry to run on, I didnt think you had steam traps on the radiators.

Jamie Hall

On your diagram, you must add a vent on the higher level return from the two radiators on the left. About where that line drops down to the wet return. There also needs to be a vent on the single vertical line from the radiator on the right. Ether that or add vents to the radiators themselves.

That radiation on the lower level, which is below the waterline, will never see steam.

ProblemSolver

Like I said, some of this was obvious. There are traps on this 2 pipe system, on the radiators in the living quarters. So it's obvious that the air vents must go on the returns at the ceiling, but because the returns are hugging the ceiling, I will have to throw a tee in on the vertical drop and keep it as high as possible.
Yes KC Jones, the baseboard will still be filled with water. Which I think is a pretty cool way to heat a garage. The problem I have with the way it is connected is the pipe on the steam main side. The steam main is just a vent to this baseboard, and that does cause an occasional hammering. Therefore, I am going to remove the vent that is there now and remove the pipe from the steam main and add a radiator vent to it. Now this baseboard will no longer vent into the steam main.

ProblemSolver

Here is what I am proposing to do.

nicholas bonham-carter

Where would the air come from which would be vented from the baseboard filled with water?
Why not put this baseboard loop on a separate circuit with a pump from the boiler, or at very least, repipe the return so that all the condensate must flow through the baseboard? What would keep the baseboard (full of water) from freezing, if the garage door is open for a while in the winter? If the baseboard were mounted higher, and piped to see steam, that accidental freezing would not be such a problem.--NBC

ProblemSolver

Removing the baseboard from the steam main does not change how it is working now. The only difference is the steam main is no longer the vent. When the boiler is in an off cycle, the baseboard is above the boilers water level, therefore it drains. When the boiler fires up and begins to make steam, the water level rises and fills the baseboard. The wet & dry returns are not insulated, thus they help to heat this garage. The garage is fully insulated with insulated doors, and all the walls and ceiling are plaster. The vent would move the air both ways.
If I did run steam through the baseboard, how would I vent it? That's a lot of work! The baseboard has been heating this garage just fine with water doing the work; actually, like I said, it's a pretty cool idea, and I don't foresee any problems.

nicholas bonham-carter

That could be a lot of water to allow to flow up into the baseboard (starving the boiler), during firing. How far does the waterline drop when this is happening? Wide fluctuations of the waterline can lead to early failure of the boiler sections, due to thermal shock.
Since this is a two-pipe system, the maximum pressure should be in ounces, for economy.--NBC

ProblemSolver

Wow good point, NBC!
Water is flowing into the baseboard now because there is no place for air to leave the radiators, so as steam tries to enter the radiators it compresses the air in the radiators and puts pressure on the wet return, thus raising the water level at the baseboard because that is where the pressure is the lowest in the system. This is why the vent is always spitting out water, especially right after the burner shuts down.
The only thing I can think of for this baseboard is to lower it below the boilers water line and make it a part of the wet return.

ProblemSolver

Here is a revised drawing. the radiators are not the problem here, it's this darn baseboard in the garage. Any more feed back would be great!!!

Jamie Hall

please refer to my comment on your other thread

ProblemSolver

I did