Trying To Understand Basement Venting Calculations

merikus

I have a 1 pipe steam system that I'm considering additional venting for, and I'm hoping someone may be able to address some questions I have.

A little background on the system. It's a 1 pipe, oil fired system with insulated mains and returns. The only oddity of the entire system is that the returns are on the ceiling directly below the mains, rather than on the floor. The return ultimately dives down below the water line once it gets to the near boiler piping. There are three main/return sets, and each return is currently vented with one Gorton #2. The mains are 1.5 inch and the returns are 1 inch. All radiators are vented with Heat Timers with the angle pattern set on max flow.

I have always felt my return venting system was a little strange. They're on quarter inch pipes and actually are tapped below the high level for the mains and returns (in other words, the return vents are tapped on T joints about 2/3rds of the way up on vertical pipes that dive down off the returns near the near boiler piping, and the vents themselves do not rise above the level of the returns). I have always wondered if these vents are doing much of anything, in part due to a suggestion that Gerry Gill gave me one day to remove the vents and see what happened, and a bunch of water went everywhere. I worry that these vents are getting closed off prematurely in the cycle, forcing venting out of the radiators.

Outside that oddity that I'd love feedback on, my questions have to do with venting my longest run, which is about 30 linear feet. The radiators on this run take significantly more time to heat up than the rest of the house, which makes me think it would be useful to vent at the end of the run. However, according to "The Lost Art of Steam Heating, Revisited" on page 197, 1.5 inch pipe contains .014 cubic feet of air per linear foot of pipe. This would lead to .42 cubic feet of air in my main. According to Gerry & Steve's work, a Gorton #2 vents at 1.1 at 1 oz. In theory, a single G2 should vent that pipe in under a minute--as should the Heat Timers. And yet, this run is very, very slow in comparison to the rest of the house, even with 6 radiators on that run all with Heat Timers. This leads to the three parts of this question:

1. Is it appropriate to vent at the end of my longest main? If so, given the numbers (30 linear feet of 1.5 inch pipe), how many Gorton #2s should I use here, keeping in mind that each G2 has a .5 inch connector, which reduces the CFM flow of an open pipe down to 2.6?

2. Is it appropriate to vent my returns at the furthest point from the boiler? I am considering doing this for two reasons: 1) I don't think my return vents near the boiler are necessarily doing anything for the reasons stated above, and 2) I worry that the natural surging of water from boiling is pushing air up my returns, causing the steam to fight against itself. If I should vent this, how many Gorton #2s would be appropriate for 30 feet of 1 inch pipe?

3. Any thoughts on my return venting oddity? I have 30 feet of returns full of air here and want to vent them as quickly as possible as well.

Thank you!

mattmia2

I think you have to figure out why the water is getting pushed out of the boiler and in to the returns. Pictures of the near boiler piping are in order as well as looking at how stable the water line is while steaming. If the equalizer is in the right place it places pressure from the supply side of the boiler on the return to keep the pressure from pushing the water out of the boiler.

Jamie Hall

You note that the returns are on the overhead, just below the mains, rather than on or near the floor. This means that they are either full of steam (or air under boiler pressure) and while they carry condensate, they are not full of water.

Now. The question is: how are they connected to the steam mains at the outer ends? Is it a direct pipe connection? Is there are water seal loop rather than a direct pipe connection? Is there perhaps a steam trap, either above or below the steam main? It makes a huge difference!

The first option there is actually not at all uncommon in a true one pipe system (yours is? One pipe and one pipe only to each radiator, with a vent on each radiator?). They would, from the standpoint of venting and connection, be considered steam main extensions, not truly returns. They should not join together above the water line of the boiler, but they can be vented with main vents anywhere from above the boiler water line back to where they become full scale steam mains.

In addition -- or alternatively -- you can place main vents on the steam mains beyond the last runout to a radiator or riser (you can do that anyway in any system, except for certain vapour steam systems).

The other options mean that these lines are dry returns, and should be at atmospheric pressure at all times.

You mention that when you took the vents off the drops from these pipes, however, that water came out when the boiler ran, although they are above the static boiler water line? That's not a bit surprising, since the water in those drops, once there was an opening to the atmosphere, will rise 28 inches above the boiler water line for every pound of steam pressure. It doesn't indicate that they are flooded when the system is operating normally, if, that is, that these are steam main extensions with a direct connection to the steam mains.

So -- the critical question is how these pipes are connected to their related steam mains. A description and pictures would help.

Now for vent sizing. Number games are all very well, however keep in mind that with main venting what governs how fast the steam moves in a pipe is only partly determined by how fast air can get out the other end. That slow 30 foot main probably could benefit from a Gorton #2, but one should be ample. That this line is very slow, at least relatively speaking, suggests strongly to me that something else is going on here.

Which brings me back to that critical question, please!

mattmia2

Jamie Hall said:

You mention that when you took the vents off the drops from these pipes, however, that water came out when the boiler ran, although they are above the static boiler water line? That's not a bit surprising, since the water in those drops, once there was an opening to the atmosphere, will rise 28 inches above the boiler water line for every pound of steam pressure. It doesn't indicate that they are flooded when the system is operating normally, if, that is, that these are steam main extensions with a direct connection to the steam mains.

Wouldn't that mean that the air venting out the vent would also allow the water to back out of the boiler and either out the vent or close the float in the vent and stop the venting?

Jamie Hall

mattmia2 said:

Jamie Hall said:

You mention that when you took the vents off the drops from these pipes, however, that water came out when the boiler ran, although they are above the static boiler water line? That's not a bit surprising, since the water in those drops, once there was an opening to the atmosphere, will rise 28 inches above the boiler water line for every pound of steam pressure. It doesn't indicate that they are flooded when the system is operating normally, if, that is, that these are steam main extensions with a direct connection to the steam mains.

Wouldn't that mean that the air venting out the vent would also allow the water to back out of the boiler and either out the vent or close the float in the vent and stop the venting?

Indeed it would, if you are considering dry returns. Which need to be placed -- and vented -- at least that magic distance above the water line. Steam main extensions, however, are under steam pressure (even if it's just air) so it's not a concern for them.

Which is why (well, one reason why) I'm a bit of a stickler about not confusing dry returns and steam main extensions. Granted, they are similarly placed in the basement -- but otherwise they function, and need to be treated, completely differently.

merikus

@Jamie Hall & @mattmia2: Very interesting points from both of you, thank you. I should note that the water issue only occurs when I remove one of the vents on the end of (what I think to be) dry returns--and that was done as an experiment. Also, the water line when boiling is rather stable, a little up and down sure, but nothing crazy. When the boiler isn't on and the condensate has returned, the water level always stays rather stable at the recommended level as well, which is good.

I'll start with a simple sketch of the system. There are three such loops in the system in total.



Here is where the (what I think are) dry returns drop down near the boiler. I do not believe they are vented the magic distance there. I feel like I saw reference to that in The Lost Art somewhere--do you know where I could find that reference? Anyway, the pictures:



Now onto the long, slow run. Here's where it terminates:





Here's what the long run looks like:



What is the distinction between dry returns and steam main extensions? I've never heard of the latter, and might be able to give you a better sense of which it is.

Thank you!

Steamhead

@merikus , what is the height measurement between the boiler's waterline and the vents on the dry returns?

mattmia2

Is it running a pressuretrol or a vaporstat and what is it set to?

Jamie Hall

That "drop thing" (as good a term as any!) has no valves or traps in it, so steam can pass right on along and zip around the corners and pressurize that smaller lower pipe. So can the condensate -- this is a parallel flow system. That makes the lower pipe -- using my terminology -- a steam main extension (and no, the term isn't in Lost Art!). The way these pipes are connected at the boiler is correct and well done --someone back in the day knew what they were doing! Also, the vent locations are correct, and will serve well as the main vents for those three steam lines, even though they aren't out in the wilderness. The air and steam don't care.

Again, however, for all concerned: those pipes are NOT, repeat NOT, dry returns. They are steam pipes. If you wanted to, you could tap a radiator into them anywhere along their length and the radiator would heat. They just happen to be continued beyond the last radiator.

Mechanically, for a pipe to be a dry return it MUST be isolated from steam and steam pressure, almost always by a trap although sometimes the isolation can be done thermodynamically with a radiator or radiators and orifices. A dry return will be at atmospheric pressure (may even be actually open to the atmosphere somewhere!). Under normal operating conditions it will never see steam.

If they really were dry returns, @Steamhead 's concern about height would be quite valid -- and, from the picture, the vents would be much too low -- but since those pipes are under steam pressure, the same as the boiler, the water in them will stand at the boiler water level and they are fine where they are.

Steamhead

Jamie Hall said:

If they really were dry returns, @Steamhead 's concern about height would be quite valid -- and, from the picture, the vents would be much too low -- but since those pipes are under steam pressure, the same as the boiler, the water in them will stand at the boiler water level and they are fine where they are.

Unless there is not enough "A" dimension- which is why I asked about that measurement.

neilc

so let's skin the cat the other way,
what pressure does the boiler make ?
keep it low and water won't climb up there,
ounces, not psi's

merikus

@Jamie Hall Thank you for that insight, that's very helpful. Your point about a steam main extension makes a lot of sense. These pipes are indeed under pressure and so that's logical they would not be considered dry returns.

This does return me to my question about vents at the end of the long main and the long extension closest to the last radiator. Heat on that side of the house is super slow. And that makes sense, one G2 is venting about 65 feet of pipe. Would it make sense to install Gorton #2s at the radiator end of the long run, and if so, should I install them on both the main and the extension, or just the main? In either case, would one be sufficient where I install them, or should I go for 2?

In thinking about this setup, it seems to me that the primary driver of pressure is the boiling of water that is pushing up the main, with some secondary pressure pushing from the other side as these are steam main extensions. To me, it would make sense then to put two G2s at the end of the long main. My concern about vents at the end of the extension is I would think that since they're so close to the boiler that the heat/pressure coming out of the boiler side of the steam main extension would shut them down before they do much. Maybe there would be a better spot for the vents on the steam line extensions?

@Steamhead: The measurement between the neutral waterline and the top of the lowest vent is about 39 inches, give or take a few inches.

@mattmia2: It is running a basic Honeywell Pressuretrol, and it is set as low as it can go.

Jamie Hall

Actually pretty much anywhere after the last radiator runout will do very nicely -- but near the end where it turns down is as good a place as any.

However. There is another possible cause: inadequate pitch on pipes. This usually would cause water hammer, but not always -- but it could cause some condensate to lie in the bottom, which would cause the steam to be slow. Therefore, before I started putting in more vents, I'd check and make quite sure that there is adequate pitch on both the actual main portion, and on the extension.