Stupid question of the day: is this a 2-pipe radiator?

SteamoPhilips

I think it is, because—try and stay with me here—it visibly has two pipes. Yes, it also has an air vent, which 2-pipe radiators generally don't. But we have some unambiguously 2-pipe radiators in this house—ancient 1874 Bundys...the house itself was built in 1870—which also have air vents. And I know from this site that two-pipe-air-vent steam is a thing.

https://heatinghelp.com/systems-help-center/two-pipe-air-vent-steam-heating/

However, my new steam guy, "Dave"—who has a very forceful manner, and whose level of expertise I'm still trying to determine—swears up and down that this is a one-pipe radiator, because the return pipe, rather than making its own way down to the basement (from the second floor), loops immediately back under the radiator and into the riser that feeds the supply valve. In other words, the outgoing condensate shares a pipe for with the incoming steam for almost all of its journey, in a very one-pipe sort of way.

The question arises because the wife has demanded a way to regulate this radiator's temperature, and doesn't want to hear any nonsense about Gorton No. 2's or Hoffman 40s. She wants a knob she can turn.

If this is a one-pipe radiator, I'll install a Danfoss TRV—as I have successfully on some of our one-pipe units.

If this is a two-pipe radiator, then we should, I think, be able to throttle the heat by turning the supply-valve knob. Is that correct?

Thanks in advance!

Jamie Hall

It is two pipe, and steam, and air vent. All at the same time. Not a stupid question at all. That was one way it was done, before reliable traps or reliable vapour pressure controls were available, and it still works just fine.

Control, however, is a problem. Usually there would be a valve on both the "inlet" and the "outlet"; yours doesn't have that, for reasons I can't determine, and that means that you can't control it as you would a regular two pipe radiator. However, you can still control it with the vent. There was a lengthy thread a couple of weeks ago on the fine art of how vents can control one pipe steam -- which I won't go into again (enough's enough) but the bottom line is that if that radiator will give satisfactory heat with a relatively slow vent, and if the boiler cycles enough either on the thermostat or on pressure or even a timer in extreme situations, you will be able to give your wife very good control with a thermostatically controlled vent. Some o them even have remote control heads with a nice knob!

EBEBRATT-Ed

@SteamoPhilips

Some pictures of the boiler and the piping at the boiler and the basement radiator connections and any vents will help.

I would put a ventrite adjustable venf on that rad for know

SteamoPhilips

Thanks for the speedy reply. I'm always blown away by how generous people are on this forum with their time and advice. You really have to work quite hard to get called an idiot. That said, I have two follow-ups:

1) Are you saying that a Danfoss TRV would, in fact, do the trick, knob-wise?

2) Also, what are the rules for pitching these kinds of radiators? I actually just turned it on for the first time in a year. We had it off because the supply valve rattled and leaked, and it took us that long to have the valve replaced. As of this moment the valve no longer leaks, but the rattle is still there, accompanied by some pretty spectacular water hammer, which I don't remember from before. Could this be a pitching issue? I know (I think) that regular two-pipe radiators don't have to be pitched, but is it different with these two-pipe-air-vent units? If so, I'll attempt some jacking up, though I'm wary of snapping something with the return loop so close under the floor.

ethicalpaul

Another nice control option for your wife would be a wool blanket that she can adjust to cover more or less of the radiator to allow out less or more heat, respectively

SteamoPhilips

Any solution that involves the word "blanket" will, I fear, be poorly received, no matter how sensible. I'm also hoping to avoid "sweater," "scarf" and "hat."

Jamie Hall

That radiator needs to be pitched towards the outlet end -- the end without the valve. Not a whole lot, but enough.

That said, when you replaced the valve did you make sure that the pipes under the floor maintained the correct pitch? Particularly the one going to the end without the valve?

And yes, I think a Danfoss TRV would probably do nicely.

SteamoPhilips

I didn't make sure of anything. My steam guy and his even larger friend did everything, and there was a ton of grunting for about an hour. And they took a break in the middle to have some wine. Very possible they misaligned something.

So after closer inspection, and measurement of the basement pipes, I'm thinking the riser for this radiator must be in the next room, five or six feet to the right of the supply valve as pictured here. Whether there's a single horizontal runout between the riser and the radiator, or one each for the steam and the condensate, I don't know, but this sounds like where the hammering's coming from.

Should these runouts *also* be pitched away from the riser? Or is it going to be a finicky business of pitching the radiator itself to flow to the left, while the pipes beneath it slope down to the right?

Thank you so much again for your help.

KC_Jones

For pipe pitch, look at steam carrying lines like the waste drain system in your house. Gravity is the only thing moving anything around. So you have to look at where the water needs to go and how it can get there. If you are pitched differently than that, then something needs fixed.

That said, the pipe feeding that radiator (valve end) needs to be pitched, over it's entire length, back to the main. The radiator needs to be pitched towards the drain end, which is opposite the valve you have. Then that drain pipe needs to be pitched back towards the main.

Your system is a 2 pipe air vent system. The drain pipe should be smaller than the feed, which is what encourages the steam to go into one end versus the other, which is important because as you noted, they both connect to the same main pipe.

If you decide on a TRV, and you say the wife doesn't want to hear about vents or anything, you may run into trouble. A TRV on steam can only make it cooler, it can't fire the boiler to make it hotter. So if the wife thinks there is anything that can be done to have that level of control, she will be disappointed. That is unless she is extremely patient and doesn't mind waiting an hour or more for temperature changes.

Before adding TRV's the system balance basically needs to be as perfect as possible (main vents, rad vents etc.), only then should you entertain TRV's as a solution that isn't happening any other way. After that they should be set it and forget it, as should the regular thermostat, but that may be a more philosophical question.

KC_Jones

Oh, one final thing. I don't know which would be proper on that system, a TRV vent, or TRV valve. I would think a valve could work even though this is more of a 1 pipe than 2 pipe system, because of the drain pipe.

Other may be able to comment on that aspect.

Jamie Hall

A valve won't work, @KC_Jones , since the steam has two ways to get into that thing. Has to be a vent.

JUGHNE

Can we see how the return pipe is connected in the basement?
Does it drop to the floor and then up to the main?....is there a water loop seal in it.....simply pipe that contains water.

EBEBRATT-Ed

We can't know for sure this is a two pipe air vent system until we see the boiler and basement piping. Could be a vapor system someone stuck a vent on.

@ Jughne is right and I also mentioned it above we need to see more of the system

Jamie Hall

I believe that @SteamoPhilips specifically said that that "return" pipe runs under the floor and back to the riser?

EBEBRATT-Ed

@Jamie Hall
@SteamoPhilips did ay tht based on whit his plumber but then his plumber says it is a one pipe system

Now there's this. Dan Holohan describes a one pipe hook up with two pipes. You drop the return from the radiator down through the floor to the basement floor and back up making a loop seal and tie it into yhe steam supply (should go in the bottom)

Stranger things have happened maybe thats what he has for this one radiator

veteransteamhvac

Can you locate the old valve? Why was it changed? Did it have some sort of adjustable orifice inside?

DanHolohan

What @EBEBRATT-Ed said. To make it work, you need a U-tube pipe going back into the return, or if there is no space for that, a horizontal check valve below a vertical pipe to allow some condensate enough space to build static pressure to open the check against the steam pressure keeping it closed on its outlet side. If either is there, then you can control the radiator with a TRV on the supply side of the radiator. This assumes the radiator is pitched toward the return.

SteamoPhilips

Here's the big picture:



with the dotted line representing my best guess as to what might be happening under the floor. When the water-hammer hammers, it does so along the full length of the dotted line. And here's a closer look at the radiator on the right, so you can see the vent and the, uh, steam trap in the lower left?



As far as I can tell, these are both fed from a single riser, and return through a shared dry return, which entwine in the basement as pictured here:



Which is to say, I think I was wrong when I said that steam and condensate share a pipe to and from the second floor. Is it possible this is just good old fashioned 2 pipe steam after all?

DanHolohan

Looks like the radiators are draining into a wet return. That's a classic two-pipe, air-vent system. It will work well as long as those returns continue to drain into a pipe that's below the boiler's waterline (a concern that comes up mainly when the boiler gets replaced). You can add TRVs to the radiators, or control them with the existing supply valves if those are working.

SteamoPhilips

I know we have at least one bona fide 2-pipe radiator. This one:



Conveniently, it's on the first floor, so I can see the pipes in the basement directly, and there are two of them:



But the other nine-ish radiators in the house are all one-pipe.

SteamoPhilips

Dan, thank you so much for weighing in. I've worn a dozen nightstands down to nubs by keeping LAOSH on them.

If this is classic 2 pipe steam, that's great news in terms of being able to throttle with the supply valves, but what does it mean for my water hammer? It definitely sounds like it's coming from one long pipe beneath the floor, with the epicenter of the noise on the far right, at the riser, but if this is a classic 2-pipe system then steam and condensate should be traveling in separate pipes. Could it be something to do with what I think is the steam trap on the smaller radiator? No-one's touched that thing in the four years we've been living here and it gives off a very "seized up" kind of vibe.

KC_Jones

You have a 2 pipe air vent system for sure.  The one you are suggesting is a bona fide two pipe is indeed a 2 pipe air vent.  I can’t remember what date “real” 2 pipe came out, but I’m pretty sure those rads actually pre date it’s existence.  Also I don’t see a trap in any of the pictures.  Dual valves with both bottom connections is a dead giveaway for 2 pipe air vent.

SteamoPhilips

For the record, here is my boiler:



Here is the near-boiler piping:



And here are the two Big Mouth vents I installed this week:





They've made a huge difference, and I think I've identified where we could benefit from another one, namely this capped-off stump right here:

EBEBRATT-Ed

@SteamoPhilips

There are many different types of "two Pipe" steam systems. This leads to confusion.

Two pipe air vent
two pipe vapor
two pipe vacuum
two pipe air vent etc etc


As Dan mentioned two pipe air vent is what you have. These are really old systems that were installed before steam traps were invented.

Within two pipe air vent there are 2 different piping arrangements

Some ran the returns down below the water line of the boiler INDIVIDUALLY.

this sealed all the radiator returns from getting steam in them. This is the best way to pipe them

Some two pipe air vent systems connected the returns from different radiators above the water line. These are more problematic. If two radiators have their supplies and returns connected together steam may get to one quicker. The steam goes through that radiator into the return of the other radiator and causing water hammer.

What to do?

Find the radiator the steam is passing through first. Try slowing the venting a little or throtteling the inlet valve to that radiator a little (make small changes at a time) See if that helps

If it doesnt help there are things that can be done like a loop seal that I mentioned several post back or dropping the return into a wet return seperately.

Read the LAOSH

JUGHNE

Looking at the basement picture showing the (red arrow) supply and the (blue arrow) return...that return drop is connected to the return wrapped in foil insulation...yes?

I assume that is a dry return that eventually drops into a wet return, so what keeps the steam out of that dry return before it becomes wet with a water seal?
If there is another rad connected the same way on that return line would we have steam going both ways and closing another air vent.

Do you have any water hammer?

Jamie Hall

Being in something of a daze on this system at the moment... I have to wonder. We have, it would seem, a return drop which connects into... a return. @JUGHNE speculates, with considerable justice, as to whether or not that is a dry return. That is to say, that it is solidly above the water line of the boiler.

Permit me to add to the confusion. Was that pipe always above the water line of the boiler? Or, just possibly, was it below the water line of an older boiler -- and thus a wet return providing a water seal between it and any other drops -- and at some point a new boiler, with a lower water line, got installed -- converting it, inadvertently, into a dry return.

Which can cause all manner of interesting mischief, not to mention odd operation and confusion...

JUGHNE

Considering that the return is only about +-6" below the steam run out my guess is that it was always above the boiler water line.
Maybe you throttle the supply down to just heat maybe 80% of the rad so no steam passes??
With this 2 valve system would you adjust the outlet valve somewhat also??

EBEBRATT-Ed

A two pipe air vent system commonly had returns from different radiators connected above the water line. These systems were very old, before steam traps were invented.

There is nothing physically to keep steam out of the returns, that's why they can be hard to control.

Some refer to it as one pipe steam with a drain line.

I have seen jobs where each radiator return drops into a wet return but this wasn't feasable in multi story buildings

Two pipe air vent can be spotted by a two pipe radiator where the supply and the return have a manual valve and the rad has an air vent and the return is smaller than the supply
.

Because the steam connection to the rad is larger than the return connection the steam "tends" to stay in the supply.

Dan talks about this in the LAOSH and they fixed the system at The General Mechanics & Tradesmen building. @JohnNY did some or all of the work

JohnNY

@EBEBRATT-Ed Thanks for the mention. I've skimmed through this and am trying to see if there is one place to create a false water line or if a few loop seals are needed. The bottom line is, as Dan said, the new boiler installation, while not done terribly (except that I despise couplings on new work), failed to take the old water line into account. So, now that the systems been altered, there needs to be some follow-up to meet the new condition of there being a lower water line which exposed some return connections to air.

DanHolohan

If any of that horizontal return piping is above the waterline of the new boiler there will be hammering. A properly placed false waterline arrangement is the cure.

EBEBRATT-Ed

2 pipe air vent is described on pages 382-385 of TLASH ...........revisited

SteamoPhilips

@Jamie Hall
@EBEBRATT-Ed 

Update: I prised up a floorboard and confirmed that, yes, there are two pipes, being shared by these two radiators. Both radiators are piped off the same horizontal supply pipe, which is fed by the same riser, and both drain into the same return. Also, there has been no water hammer since the day I turned these radiators back on—the day I started this thread—so I’m dismissing it as a fleeting startup phenomenon, presumably caused by water that collected somewhere during the year-plus shutdown.

There is still quite a lot of…drama between these two radiators, especially upon startup in the morning. Both hiss more aggressively than our other radiators—loudly, with vents opening and closing every few seconds. There’s some occasional gurgling and churning in their shared pipework that makes me think the return of water hammer may not be far off. And at the end of the heating cycle one of the vents gives a long, drawn-out exhalation like a French film star that I’ve never heard from another radiator.

But I’m going to refrain from wasting anyone’s time with these mysteries until I’ve replaced the ancient, clearly seized-up steam trap on the smaller radiator, studied the relevant pages in LAoSH, and made absolutely sure that I have adequate main venting.

My only questions at this time are:

1. Can you confirm that, this being a 2-pipe system, I’m cleared to use both these radiators’ supply valves as throttles? Can you ride the supply valve on a 2-pipe-air-vent radiator with the same abandon that you can a regular 2 piper?

2. What is the general philosophy for venting a radiator that’s being valve-throttled? If heat-control is taken care of at the valve end, does that free you up to use a fast vent to get the air out as quickly as possible? Or do you still manage heat primarily with vent size, and use the valve for fine tuning?

3. What should I do about this defunct and long-discontinued Victorian steam trap?



Replace it with a modern trap? (If so, which one?) Or should I take this opportunity to pipe the return valve straight into the return line, as on its partner radiator, thus making it (I think) more of a classic 2-pipe-air-vent situation?

Thanks again for everyone’s help.

Jamie Hall

That's not a trap -- that's a valve. Equally ancient, perhaps, and certainly equally Victorian -- but a valve. If you are feeling very very brave you could try operating it -- but I wouldn't push it too hard.

SteamoPhilips

That's great news, I think. If it's a seized-up valve, it must be seized in the open position, otherwise the radiator would be full of water. So I think I'll leave it in peace.