Two-pipe steam radiator w/attached vent

Rob Pickard

What's the likelihood of a pipe snapping? I can't see what these pipes are attached to, but you may have some idea of how a pipe would typically be secured below the floorboards.

Rob Pickard

Should my radiators have vents?

In my condo unit I have 4 two-pipe steam radiators. The pipes are on the bottom of opposite ends of the radiators, and three of the four have an air vent opposite the inlet pipe about 3/4 of the way up the end (above the outlet pipe). Only one of the vents actually works, or appears to, because air will come in and out depending on the point in the cycle. The vent hole on the ventless radiator is closed with a bolt. The three radiators without a working vent seem to make more gurgling noises than the working-vent radiator. These appear to be what Dan refers to as missing-link radiators, but I wanted to get an expert opinion because most of the literature says that one-pipe radiators should have vents and two-pipe radiators should not.
Where would I go to find the correct vent for these radiators?

JK_3

First point is that there should be no vents on two pipe rads. Point two is that because you don't hear the other two vents does not mean they are not working (you should not hear the vents working in a properly set up system). The gurgling sounds could be improperly pitched rads,air being sucked in through one or more vents,even a condensate return pump that is defective depending on the piping configuration. Another possibillity is one or more defective steam traps. More information about the system may prove usefull in determining where the problem(s) lie.

Rob Pickard

JK- I just talked to the heating contractor who services the boiler in our building, and he said that he didn't understand why the vents are there, but that in the past someone probably decided to put them on as a stopgap measure. Do you think I should remove them, as he doesn't think anyone else in the building has them?

I wish that I had more information about the system as a whole, or whether any of the other hardware on the system is not operating properly. The only things I know are that the radiators provide enough heat, they make banging noises mostly at the start of a cycle or when I turn off the regulators (which I think is explained by water in the pipes that is out of my control), and the incoming steam sometimes appears to be entering the radiator unevenly, causing the floor nearby to shake.

JK_3

Since the vents do not belong there that would be my first step. this may correct all the problems or we may find that someone added them in as an attempt to correct a problem which may still need to be corrected properly.

Steamhead (in transit)

Hold it, guys!

This really sounds like "the missing link"- what's known as the two-pipe, air-vent system. In this system the radiators are vented but the return lines are not. This system almost always has shutoff valves on the radiator return connections as well as the supplies.

Rob, if you're not sure what you have, post a few pics before doing anything.



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Rob Pickard

Here are some pictures of the four radiators, one without vents and three with vents. The vent that appears to allow air in and out is the one in the final two pictures (taken from above).

Steamhead (in transit)

Oh boy

it looks like this might have been a 2-pipe air-vent system, and someone has put traps on it in an effort to make the TRVs work.

Next thing to check is where the return lines go. Are they connected to each other above or below the boiler's waterline?

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Rob Pickard

I will ask the guy who currently maintains the boiler to see if he knows. What about this setup makes you think that it's a two-pipe air-vent system and not just a two-pipe system with air vents that shouldn't be there? And what are the names of the valves at the inlet and outlet?
Thanks,
Rob

Garret

Pros can correct me if I'm wrong, but I think seeing supply valves at the bottom is one give-away. A couple of your radiator air vents also look old... if they were added recently, they'd be, er, shiny!

The two-pipe air vent system had valves on both sides of the radiator, usually at the bottom. This was basically a two-pipe, one-pipe steam system... steam originally would drive into the radiator from both the supply and return sides, pushing air out the vent.

After 1903, after the invention of the thermostatic trap, they refined the two-pipe system. The supply side valves moved to the top, the return side got the new thermostatic traps instead of a valve, and the air vents were removed from the radiators and put in the basement, where they were quieter. That's the system I have in my house...

So it looks like an attempt was made to turn your system from the tricky "missing link" air vent system, into the newer style. You have nice thermostatic valves on the supply side, which is potentially a good thing (because they help balance your system by preventing overheating -- important in a multi-unit rental bldg), and they've put new traps on the return side.

I'm not sure about the vents on the radiators. I think it all depends on what the upgraders did to the rest of the system. The air has to go somewhere, or the rads won't heat. I'd be curious to see what the piping looks like in the basement... did the upgraders also install venting in the mains and returns?

-Garret

Rob Pickard

Garret- I think that you've correctly analyzed this. I've learned that about ten years ago after the building converted to condos the owners decided to make the change you've described to the heating system. However, I don't know whether the main vents that presumably were installed are adequate, and the level of water hammer that I hear in the pipes makes me think that something is out of alignment.

My guess is that I probably don't need the vents because the one radiator that doesn't have them heats perfectly well, and no one else appears to have them.

It seems like it might be worth my while to pitch the radiators though, because in the original configuration you've described it seems like pitch would be immaterial because both pipes would've been outlets for the condensed steam. Do you have suggestions for pitching radiators? Would I use a car jack to lift them, and if so, is there danger of the inlet pipe breaking as it gets pulled slightly out of the flooring?

Garret

[duck] Who me?

I'm just a homeowner and steam enthusiast, parroting what I've absorbed from Dan Holohan's Lost Art of Steam book and this site...

Steamhead and other pros will have answers backed with genuine experience to guide you... But if you're game, I'll make things up again.

With your system, I think you should have a little pitch toward the return side. In a typical two-pipe system, you can get away with a level radiator because the supply valve is on the top... but with what you have, you want to make sure the trap is lower than the supply valve, or condensate will try to drain backwards into the supply side.

So grab a level and check that the pitch is always heading toward the return side. I've used some tricky car jack shenanigans before to lift mine to remove carpet... you can lift 1/4" or so, no trouble at all. Just go veeerrrrry slow and carefully so you don't snap a pipe.

Once you get the supply side up high enough, just put some washers or something underneath to shim the feet up. Cast iron rads are incredibly heavy (hundreds of lbs), so be careful.

If you can remove those vents safely, removing them and plugging the holes is an easy thing to try out. Seems to me that if you have traps on your radiators, you don't need vents anymore. Just spray a little pb blaster on the threads first if they seem to have rusted shut, and again, go slowly and cry uncle if it doesn't give easily. Since you don't own the system, you don't want to buy in too far.

-Garret

Steamhead (in transit)

Could be a vacuum problem

If a TRV closes when there's some steam in the rad, the steam will condense and pull a vacuum. If there's any steam in the returns (there should NOT be) it can be pulled into the rad thru the trap. This can cause banging, and is definitely bad for the trap.

I think you can get little vacuum breakers that screw into the 1/8" pipe thread holes where the vents were.

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