Detailed Main Venting Questions

SteamySwede · November 2012

Hi experts – I could use a bit of guidance on some main vent issues that I don't know enough to handle from Dan's books.

 

I have a ‘20’s era two-pipe vapor system with a recent Weil-McLain gas-fired boiler. The house is 4100sf and has 25 radiators of varying sizes mostly equipped with Hoffman 17a or 17c traps. All in all, I can measure about 198’ of 2”, 2 ½” and 3” main pipe around the basement in a bunch of different branches before the risers. The dry returns all have main vents where they connect to the wet returns. As it is a 2-pipe system, there is really no venting on the steam mains with one exception noted below. 

 

I’ve been replacing various radiator trap elements as the radiators stop heating which has solved all the individual radiator problems to date. Many of the radiator valves are effectively petrified so I believe I have them all in the wide open position but hard to be certain. Overall the system works great but I have a balance/timing issue in back of house which was an addition in ‘30’s or ‘40’s and runs off a separate line of main supporting at least 6 radiators (some are quite large). This portion of steam main tees off another portion that works great so I don’t think I have an issue with getting steam to it. The back of house barely has a chance to warm up while remainder is warm enough to turn off system. If I leave heat on high, everything eventually gets hot so steam is flowing everywhere I need it eventually. I’ve been reviewing the main vents to check adequacy and have found a few things that I could use some input on:

 

Cool back of house:

- The steam main serving this portion of house is at least 20’ of 2” or 2.5” main and then it disappears into a slab and is uninsulated from what I can tell (nothing I can do). There is probably another 50’ of main piping in the slab to distribute the steam around to 4 first floor radiators (size unknown) plus risers going to second floor for 2 or 3 more radiators. There is no main vent on the steam side (correctly from what I am reading) and only a Hoffman 75 venting the dry return for all the radiators. Also, this dry return is quite far from any of the radiators so there is a long run through the slab back to the vent that needs to be vacated. The Hoffman 75 on the dry return seems to continue venting air nearly twice as long as the main vents on the remainder of system which leads me to believe it does not have sufficient capacity and is slowing down the steam progress in this part of house. I don’t know the vent capacity I need as I can’t trace the pipes once I get to the slab nor do I know the capacity of the Hoffman 75. Is it comparable to a Gorton #2? Is there a higher capacity Hoffman or do I just need to add a second return vent and see if the balance improves? I realize the lack of insulation on this long run of pipe in what becomes a cool/cold slab is less than ideal and could be part of the slow heating issue but not much I can do about that. 

 

2 potential issues do not relate to cool back of house issue:

1) I found a Dole 103 vacuum vent venting about 19’ of 3” main steam pipe. This is the only vent on the steam main. This main vent is just an intermediate vent along the length of one section of the main slightly ahead of a major branch in the main. It is not at a terminal point where it connects to a dry return. From what I read, any vacuum vents are a bad idea on a gas-fired non-vacuum system and this one is likely inadequate to begin with. Please confirm if I should change or cap this vent and a suitable replacement if applicable. 

2) I have a Hoffman 76A (is this the same as a 76?) on a single small radiator dry return upstream of additional dry return lines that vent another 4 radiators with a Hoffman 4A. So in terms of flow: Rad>Vent-76>4 add’l Rad dry returns>4A>Wet return. I’m not sure if the system should be looked at in total or only for what is upstream of a specific vent. Again, it is a vacuum vent that maybe should not be there but also seems like overkill in terms of capacity if it is only venting the one small radiator upstream. All radiators on this system seem to heat fine so no performance issues currently. So 2 questions really: 

a) should I change the 76A and to what?

b) With that change, do I have enough venting capacity on this return line for all 5 radiators? I don't know if I should maybe move the 4a upstream to the first venting location and then put a larger capacity vent at the end of the line. 

 

Thanks in advance for any input. Naturally let me know if I've failed to describe something essential.

Rod · November 2012

Info on Venting

Hi- First of all I must mention that I’m a homeowner with a 1 pipe steam system and not a pro so my knowledge of big steam systems is minimal.

   Reading over what you have written it would seem to me that the main problem is that the system is severely lacking in venting capacity.

    Mains on a 2 pipe system generally have either need main vent to get the air out of the main combined with a drip pipe to a return to remove the condensate or a pipe with a trap connecting the end of the steam main to the return main. Air leaves the steam main by way of this connecting pipe and escapes by way of the vent (s) on the return main. The trap allows condensate and air to pass but not steam. In this case the return vents are vent both the steam mains and the

radiators so they need to have a large volume of venting capacity which would probably mean multiple vents as a single vent wouldn't be enough.

Main Vents-   Capacity wise 1 Gorton # 2 is equal to 3 3/4 ea. Gorton #1 (s) or 2 ea. Hoffman #75 (s). The Hoffman #76 (vacuum vent) has a little more than ½ the venting capacity of a Hoffman #75.

   I would highly suggest that you get a booklet on venting available in the Shop section of this website. It has the venting capacity for all types of vents and traps. The book is called: “Balancing Steam Systems Using a Vent Capacity Chart” It’s written by two steam pros and is one of the most useful books I have. It’s available as an e-book at a very modest cost and you can immediately download it. Here’s a link to it:     http://www.heatinghelp.com/products/Steam-Heating-Books/25/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek

The authors of the book mentioned above are Cleveland steam pros and have a great website   http://www.gwgillplumbingandheating.com/ which has a lot of good info on steam heating. Be sure to check out the sections on venting and 2 pipe systems and also an article on a technique that Gerry Gill calls “Air Locking”. When I read your post it seems to me that your distribution problems to remote locations might be cured with this technique. Here’s a link to the article: http://www.gwgillplumbingandheating.com/webapp/GetPage?pid=608

- Rod

SteamySwede · November 2012

Thanks!

Rod,

Many thanks for the input. I have most of Dan's books but had not seen the the balancing e-book and have ordered it already. From what I had read in Dan's books, I had come to conclusion that main steam vents were for 1-pipe systems like yours and not for 2-pipe systems as the steam can rapidly push air through system.

I'll review the resources you guided me to in order to learn more. Much appreciated. Happy Thanksgiving.

SteamySwede · November 2012

Pipe Step-down?

I was taking a closer look at the Hoffman 75 vent on the large return from back of house and noticed that it has been mounted inside of a broken off pipe. The return on this loop is one inch down to the wet return. However, the vent seems to have been replaced and the pipe going up to it broken at that time. The fix was to thread a 3/4" pipe into the 1" pipe for the mount. In effect the dry return steps down to a 3/4" pipe although venting a 1" return. Seems like it would make sense to restore the pipe to the vent to a full inch, yes?

Would this imply that I should install at least 2 Gorton' #2's since their inlets are 1/2" if venting a 1" return?

I'd still value any input on whether there is rational to having the vacuum vents that I found on the main steam pipe. They seem out of place from what I can read.

Thanks for the input

SteamySwede · November 2012

Pipe Step-down?

I was taking a closer look at the Hoffman 75 vent on the large return from back of house and noticed that it has been mounted inside of a broken off pipe. The return on this loop is one inch down to the wet return. However, the vent seems to have been replaced and the pipe going up to it broken at that time. The fix was to thread a 3/4" pipe into the 1" pipe for the mount. In effect the dry return steps down to a 3/4" pipe although venting a 1" return. Seems like it would make sense to restore the pipe to the vent to a full inch, yes?

Would this imply that I should install at least 2 Gorton' #2's since their inlets are 1/2" if venting a 1" return?

I'd still value any input on whether there is rational to having the vacuum vents that I found on the main steam pipe. They seem out of place from what I can read.

Thanks for the input

Rod · November 2012

Main & Return Vents on a 2 Pipe System.

Hi- Attached is a drawing of two typical ways of dealing with Steam Main venting on a 2 pipe system. The one that has the drip on the end of the Steam Main must have a large capacity main vent to let the air out of the steam main other wise the air would have to travel through the radiators out out through the main vent located on the Return Main. This would make the system much slower to respond and cause other problems like "short circuiting"

As for the Hoffman #76 (vacuum vent) on the main, If this main is dripped then you definitely need a main vent, though I really see no benefit of vacuum vent as the system not having vacuum vents on the return, is no longer being run as a vacuum system.

Since you now have the Venting Book you can see that the Hoffman #76 has a little more than a 1/4 the venting capacity of Gorton #2 so would benefit being replaced by a Gorton #2.

Return Venting- As you can see in the attached drawing, if the end of the steam main connects to the Return Main by way of an F&T trap, ALL the air in both the Steam Main and the Return Main PLUS all the radiators has to be vented by the Main Vent on the Return Main. Since this Return Main Vent should never see steam (IF all the traps, both the radiator traps and F&T trap are operating properly) you could theoretically use just an open pipe to do the venting. However the problem with having an "open pipe" for a vent is that if one of the traps broke and steam was released into the Return pipe, it would then be released out the open pipe and flood the room with steam. This probably would panic the occupants and after seeing clouds of "white smoke" coming out of the boiler room they would call the fire department! To stop this embarrassment happening, main vents, that will close if steam ever reaches them. are needed on the vent pipe!

You stated that the vent pipe is now 3/4 inch rather than 1 inch. Again using Gerry Gill's excellent Venting Book, a 3/4 pipe will support 4.3 Gorton #2(s) and a 1 inch pipe will support 5 Gorton #2 (s) I'd go with the 4 Gorton #2 (s) and mount them on a "Antler /Menorah" (see attached drawing by Brad White) Be sure that all drip pipes from mains and returns only connect together well below the boiler's waterline level or that they go directly the the Wet Return without connecting. This stops any cross feeding of steam.

- Rod

SteamySwede · November 2012

Pic for detail

Rod,

Thanks for help. I have not rec'd the venting booklet yet - presumably due to the holiday but am trying to advance the ball while I have some time so your input has been helpful.

My main piping is a hybrid of the two diagrams you provided. There is a main drip to the wet return at the end of each loop, BUT, there is ALSO a connection through a box-shaped valve to the dry return slightly above the water line / wet return. See attached pic. I'm not sure if these are F&T traps or some other form of trap but am hoping they are venting my steam mains. They get hot on the hot side and stay pretty cool on the cold side but I'm not sure how to tell if they are venting the steam mains. Any ideas?

I will replaced the Hoffman 76 and Dole with some Gorton 2's as well as add substantial venting to capacity to the dry return on this cold loop.

I went ahead and did some preventative maintenance today to eliminate the possibility of bad traps by replacing them all on this cold loop. They looked old although I'm sure they age quickly. One was dated from 1939 on the cap with the integral trap on a Hoffman 12A. That can't have been good. One trap was completely empty so steam was getting through to the dry return although perhaps limited by the poor venting. This may be part of the heating challenge. We'll see.

Your thoughts on the steam main connections to the dry returns is appreciated. Thanks.

Rod · November 2012

Waterline Height?

Hi- This looks like a system with a drip at the end of both the Steam Main and the Return Main. The check valve (one way valve) (see attached photo) isn't really needed as long at the boiler's waterline is above "H". I'm assuming the boiler's waterline is somewhere around the blue dotted line I drew in the photo? Where are the main vents located ? I labeled the different pipes I could see with letters . Where do they go?

- Rod

SteamySwede · November 2012

Lower Water Level

Rod,

Thanks for the ID on the check valves. I assume they are intended to vent the steam main condensate back to the return without permitting steam through to the dry returns. If that is case, however, I have no venting on the steam mains.

The water level is much lower than your line. It is below the H and at the point of the two drip connections on this loop of the wet return, the water level is below the wet return. As it descends further, the water level fills the return between the last drip and the boiler.

While that would seem to raise the risk of steam getting into the dry return, it does not seem to pass through those check valves. Maybe the opening pressure is above the system operating pressure (pressutrols set as 1/2 psig + 1 diff). Sound right?

As for the pipes you identified:

A- Steam Main

B- Branch off the steam main to a riser

C- Branch off the steam main to a riser

D- Riser off pipe C

W - Return from 2 radiators

V - Return from 2 radiators that connect at Y and Z

X - Return that connects to dry at the point you marked Y

Also buried in that picture is Hoffman 4A vent at the top of the vertical dry return drip. It is venting all 4 radiator returns and possibly the steam main if the check valves are not doing so.

Rod · November 2012

Boiler Waterline

Hi- Thanks for the info on the piping in the picture. My knowledge of vapor systems is only very basic and I'm uncomfortable with the Boiler Waterline as low as you say it is. However, whether or not this is you can get away with this is beyond my realm of experience and therefore I wouldn't want to advise you on a course of action.

My thoughts are that the original boiler water line may have been much higher and therefore you need to use a "false waterline" (Page 28-31 TLAOSH) Possibly one of the pros can be of more help to you. Frank Wilsey, "Steamhead", comes to mind as the one to ask as he is a wizard with diagnosing old vapor systems.

- Rod

SteamySwede · November 2012

Great reference

Rod,

Thanks for that reference in the "manual". I've read and reread it several times now. My system certainly shows the design issues described (new boiler with water line befow what was a wet return). However, I seem to have limited symptoms if any - certainly no hammering. I get a bit of short cycling - a minute shut down periodically - that I can't determine the reason for but will install a low pressure gauge to see if I'm building to the 1.5 psig cut out pressure and go from there.

I don't seem to be a candidate for a false water line. I have about 45" of A Dimension. Not nearly enough for a 4' U-loop plus the 28" A dimension. I do have the option to just lower this wet return loop without too much trouble. I'll need to check the level of the other wet return loop. It's well below the boiler water line where it reaches the boiler room but runs behind finished basement walls around most of the house so not sure of the level by the main drips.

If I replace the wet return, I may as well repipe the dry return drips staight into the wet return to eliminate the old check valves as well.

I'm not sure if this issue is creating the slower heating loop issue i have though. I've removed my Hoffman 75 and another vent cap so I have a 3/4" and 1/2" pipes venting direct to atmosphere to chack for a difference in heating but negligible. I think I need to add the steam main vents to further assist the process and see where I am.

Thanks for your guidance on this thread. It's been helpful to me advancing my knowledge of my system over the holidays.

SteamySwede · November 2012

Rod is a Genius!

Rod,

You da man! My little brain finally put 2 + 2 together with your help.   The air-filled wet return that you identified is likely my issue with the cold loop!

I'd been assuming any flow issues I'd have were a result of steam getting into the dry returns to stop the flow of steam but my dry returns have tested out fine and the new traps should have assured it. The checkvalves in the drip connections do not let steam into the dry returns either. So why no heat? Bad venting on dry returns? I opened pipes and got negiligible difference. Hmmm?

What you could not see from the photo, is that there are two steam main drips to this air-filled wet return. One loop (the cold loop) is very long, likely 100' or more before the steam main returns from the slabbed portion of house back to boiler room where the drip is. The other loop (which heats fine) is no more than 20' before it reaches the drip (the one in the photo). As you pointed out, the steam main drips are not trapped since they are supposed to be terminating into a wet return.

Here's my hypotheses: the steam from the shorter loop is racing down the steam drip, across air-filled wet return up the other steam loop.  There is nothing to stop the steam and that long loop (with nothing but one dry return vent on a lot of pipe) has a lot of air that is seeking to leave the system so the pressure is low. We know the steam follows the low pressure....

Eventually they meet somewhere in the loop, stop the flow, stop the heating and build some minimal pressure (given multiple other steam loops, dry returns, etc. it does not stop whole system from flowing) that is short cycling the boiler given the low cut-out pressure. Does that make sense?

It seems like it would explain why the radiators off the short loop are heating fine and not showing any ill effect from the air-filled wet return as well as why the longer loop is not heating properly.

We're not getting any hammering if the air filled wet return or in the cold steam loop (although I hear more pipe creaking in the cold loop but thought it was expansion against concrete in the slab).

Any insight on what happens when steam meets in the middle of a loop with steam coming from both ends? I assume whatever air is trapped in system between the steam flows acts like a buffer and the flow of steam just stops. Any radiators being served by the steam (before they reach the air buffer from either end) continue to get steam as the radiator traps vent, but if the air buffer includes a radiator, it will not get any heat.

I'm hoping I'm not out to lunch here...the fix seems pretty easy with just lowering this this air-filled wet return back under the boiler water line. Thanks for any thoughts or perspectives on this.

Rod · November 2012

Venting

Thanks for the complements though all I’m doing is passing along what Dan’s steam books and from others on the Wall have taught me.

I think you’re on the right track. I find it helps to think of yourself as a molecule of steam and to keep in mind that what moves steam along is pressure differential.

On a two pipe system with drip pipes, ALL drip pipes must end in the Wet Return so they are sealed off by the water. Keep in mind that a “Wet Return” is a pipe filled with water and by definition is below the boiler’s waterline. (That’s why they call it “Wet” !

)

How a 2 pipe system should ideally work on a dripped steam main.

1. Steam enters the steam main from the boiler

2. Since we want the steam to fill the whole steam main first so as to reach all radiators at the same time, we place a large capacity vent(s) on near the end of the main (after the last radiator lateral) to provide the pressure differential.

With NO MAIN VENT- With a dripped main if there is no main vent (s) at the end of the steam main. The steam will enter the first radiator it comes to and travel towards the Vent on the Return Main.( high to low pressure!)

When the steam reaches the radiator trap, the trap will close and steam will then move on to the next radiator down the steam main. Since the vent (s) on the Return Main is venting BOTH the steam main AND the radiators one at a time, this is a very slow process especially with a lot of radiators on one main. If the thermostat is located in a room which has a radiator close to the boiler end of the steam main, it is quite likely that this room will reach the set temperature on the thermostat (and turn off the burner ) before the last radiator on the main begins to get steam and has warmed up.

Air Locking a Two Pipe System

On a long mains circumstances may arise where even with good venting on the steam main, the lure of the pressure differential caused by large venting capacity on Return Main may cause the steam to “short circuit” through the radiators and not finish its journey to the end of the steam main and the radiators located near there.

Gerry Gill has come up with an ingenious method he calls “Air Locking” . This is done by using an electrically operated valve on vent pipe going to the Return Main Vent(s). This valve remains closed until a sensor at the end of the steam main senses steam has filled the steam main and at which time the sensor sends a signal that opens the valve and the Return Vents become operational. Using this method guarantees that all radiators on the steam main receive steam at the same time. Here is a link to Gerry Gill’s article on the Air Locking System.

http://www.gwgillplumbingandheating.com/webapp/GetPage?pid=608

- Rod

SteamySwede · November 2012

Venting Steam Mains on 2-pipe?

I received Gill's write-up on balancing systems with venting and wanted to clarify something that I can't reconcile.

The booklet is clear to vent mains and then the radiators on one-pipe systems as are Dan's books. However, when Gill discusses the trap flow rates (which only apply to 2-pipe systems), it's unclear if this is in addition to venting the mains. Further, on pg 126 (col. 1) of TLAOSH, Dan specifically states that 2-pipe systems should ONLY have vents on the dry returns as opposed to 1-pipe systems that should have the mains vented.

Quote: "Just make sure the main vents are near the end of the dry return, after the radiator returns, not at the end of the steam main as they would be in the one-pipe system."

Rod - I know you had mentioned you had a 1-pipe system so I would understand if you had not focused on this text in the 2-pipe section and I don't see the clarity in Gill's write-up to disregard Dan's emphatic point.

Any input appreciated as always. Thanks.

Rod · November 2012

Venting on a 2 Pipe System

Hi- You just have to look the how the end of the steam main is handled. Take a look at the drawing of the main I sent you in an earlier post.

If there is a pipe with an F&T trap at the end of the Steam Main that connects the steam main to the Dry Return Main, then the air (and condensate) in the Steam Main pass through the connecting pipe, through the trap, into the Dry Return Main, then the air from the Steam Main (and air from the radiators) escapes from the system by way of the Dry Return Main Vents.

If there is just a drip line to the Wet Return (and no connecting pipe with a trap) then for the air to be able to escape from the Steam Main, so there must be a Main Vent on the end of the Steam Main. In either case the Steam Main is vented! If there isn't a way for the air in the Steam Main to get directly to a Main Vent (either on the end of the Steam Main or by way of the connecting pipe & trap to the Dry Return Main Vent) then the air from the Steam Main would have to vent through the Radiators. If the Steam Main vents through the radiators this causes distribution problems as the steam doesn't reach all the radiators at the same time.

In the LAOSH I believe that Dan is referring to the diagram on Page 126 which has a connecting pipe and trap. In this case there is only ONE Main Vent (position) which is on the Dry Return. To me it would seem that he is comparing this with the 1 pipe system which also has ONE Main Vent (position) which is on the end of the steam main. In the case of the dripped main (no connecting pipe & trap) there are TWO Main Vent (positions), one on the end of the Steam Main and one on the Dry Return.

To quote Gerry Gills' famous saying: " Before a steam trap is a steam trap, it's an air vent!" The Idea is to get balance so that all radiators heat evenly the size of the radiator trap (trap rates) needs to be considered much like the size of the radiator vents on a one pipe system. The difference being that you can slow a two pipe radiator down by throttling the inlet valve if necessary.

I think the possible confusion lies in that Dan was talking about Main Venting and Gerry radiator venting. One of the things I find confuses people is that on the 2 pipe system with a connecting pipe and trap, the Main Vent(s) on the Dry Return have to be able to accommodate the venting of both the mains and all the radiators

- Rod

SteamySwede · November 2012

Thanks again

Rod - thanks again. I see your point that the F&T trapped ends of mains would permit more rapid venting of the steam mains on a 2-pipe system compared to the drips that I have (all venting flowing through the radiators). I'll take another read through the material with that in mind.

Rod · November 2012

Venting Steam Mains

Hi- The design problem that the installer faced with having a drip pipe on the end of the steam main was that a Wet Return was needed so the drip pipe could be attached to it.

This is why you see a lot of steam mains running in a circle around the basement and ending near the boiler.

The benefit of using a connecting pipe and trap was you could run the steam main in a straight line away from the boiler and then connect the end of the steam main to the Return Main (with the trap to keep the steam in the steam main) and then run the Return Main parallel to the steam main back to the the boiler. This configuration was easier /quicker to install and saved on pipe!

The vented main with a drip is in some ways is more efficient as the main has its own vents and doesn't need to share them with the radiators. Also there isn't a F&T trap that needs to be maintained.

- Rod

Detailed Main Venting Questions

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