low pressure

[Deleted User]

I recently installed a new megasteam boiler in my 300 year old house. I have a one-pipe system with 18 radiators in a two story house. The new boiler works very well but I am still having issues balancing the system. The heat is having a hard time reaching the radiators at the end of the line. I replaced the main vents with the new boiler but I have not changed the radiator vents. I have Varivalve vents and I believe they are not fully closing. The system runs at 0- 0.25 lbs of pressure. I have a 0-5 lb gage on the boiler and it barely moves unless it is on a long cycle.  Steam is very dry with no spitting. My fuel consumption is also higher than i expected and I suspect that the vents are the issue.

 

Question: what is the best way to vent a one-pipe system. Do I need adjustable vents, or is it better to size them to the radiator / location. Is low pressure a good thing or should I be building pressure during the heat cycle?  

Thanks,

Mike  

Jamie Hall

Main vents

Main vents -- good big ones -- are really important on one pipe steam.  How big, and how many, depend on the pipe size and length -- but it is not uncommon to see installations with two or three Gorton #2s on each main.  You don't say what you replaced the main vents with, but if you meant that the Varivalves are the main vents... they aren't big enough.  Sorry about that.  Ideally steam should reach the farthest radiators within five minutes of hitting the nearest ones -- even on a very big system.  Less on a smaller one (a possible rule of quick comparison -- a minute for every 15 feet of main, tops).



Incidentally, all your mains are insulated, aren't they?  If not, do it -- that will make a huge difference.



Adjustable vents on the radiators are very helpful in balancing things, but it is not worth fiddling with them until the main venting is correct.



Your system pressures are fine.  Raising the pressure settings won't help a bit.  In fact, above about 2 psi, rasing the pressure will make things much worse.

David Nadle

Vairvents

I don't use varivents any more because I've had a couple of them get stuck shut after about one season. That might be the reason some of your radiators are cold. Remove them and make sure they can pass air.

Brad White

The best resource

is Gerry Gill and Steve Pajek's e-book available on this site:



http://www.heatinghelp.com/products/Books/5/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek



A take-off of your piping by size and tallying your radiator volumes (there is another chart for that somewhere, I have one...), you can pretty much nail down your venting strategy in an afternoon.



I tend to favor Gorton air valves (vents). I have used Heat Timer Vari-Valves but have found them to be a bit noisy and spit like angry llamas in systems with otherwise dry steam. (Never did figure out why).  But the Vari-Valves do have very high and yes, adjustable capacities.



Follow Jamie's advice on insulating and using Gorton #2 main vents, not using Vari-Valves for main vents. As he said, your low pressure is doing you a world of good. But low pressure also means best possible venting as you know.

Phil_17

low pressure is good!

The lower the pressure the better (generally speaking).



As others have said, big vents you your mains are essential. After that, it's important to get the steam to each of the various radiators at reasonably the same time. After that, generally the vents should be sized according to the size of the radiator they're attached to.



A trick that I've adopted (though not seen mentioned much on this site) is to actually put two vents on the radiators that are on long run-outs from the main. You can put a reasonably large vent (like a Gorton #6, or C) on the radiator at the end above the radiator valve, and then either an adjustable or significantly smaller vent at the other (normal) end. In this configuration you get large venting performance to quickly get steam to the radiator, but then the radiator will fill more slowly and allow all the radiators to fill at about the same rate (all of them will be 1/4 full at the same time, 1/2 full at the same time, etc.). At least in my house and with my configuration this works really well. The only down-side to this approach is that you need to get the plugs out of the radiators in order to add the close vents, and that can require drilling if the plugs are not willing...

FJL

Plug and Second Vent

I never even noticed the plug above the radiator valve until you mentioned it. In any event, my comment is that you are the first person who has mentioned putting the second vent on the other side of the radiator. Dan's book and other folks have suggested adding a second vent for a large radiator but that has always been by drilling a second hole above the existing vent. I had assumed that the radiator vented better by having both vents farthest away from the radiator valve, but I guess you have had success with placing one vent on each side.

Phil_17

second vent

I use the second vent as a proxy for a main vent, not so much as a "radiator" vent.



In my case I have two mains in the basement, but the last take-off from one of the mains has a long run-out (about another 20' of 2" and then another 20' of 1 1/2), and all the radiators on that leg ran cold. Basically the steam got to the radiators that had short take-offs from the mains (2-8' of 1 1/2" or 1 1/4" pipe) first and (especially in the shoulder seasons) heated those rooms nicely and satisfied the thermostat before the outlying rooms got enough (any) heat. If I just put BIG vents on the outlying radiators then that would help in the shoulder seasons, but those rooms would then overheat in the cold weather :-(



With my technique I get fast venting on the long run-out until the steam reaches the radiators (shutting the close-in big vent right away) and then the smaller vents allow the radiator to fill evenly with all the other ones in the house.



I've seen some discussions in the past where people talked about putting a "main" vent near the valve of a radiator (or at the top of a long run, like a second or third floor feed), but it seems like a lot less work to just use the tapping that is already provided and have the ability to tune the venting on a room-by-room basis.

[Deleted User]

low pressure

Thanks for the information, this gives my some idea of why I have a problem getting even heat.



I do have insulated mains, I have not had a chance to insulate my near boiler piping but I intend to "see pictures". The system has (2) long mains around the perimeter of the house. The first is approximately 120' before it hits the last radiator, the second is about 70'. They have 70' dry returns that drop at the boiler, all insulated. Both mains have (1) vent-right #35 main vent where the return meets the boiler. I also run the Vari-vents wide open on the radiators on the end of the mains on the second floor.

When the system fires it takes about (5-8) minutes for steam to hit the main vents at the boiler. The challenge that I am having is getting heat to the end of the line on the second floor, some . I did a test and closed some of the first floor radiators and the steam built very quickly on the second floor. It also built about 1.5-2.0 psi of pressure. Water is clean and the site glass is steady there is no hammer during the cycle. Boiler is a Megasteam 629 200k-BTU feeding 400sqft of radiators + mains.



I think that I am venting to much on the first floor with the Vari-vents, even if you close them all the way they still vent. I think that the radiators are not holding the steam because they are venting to quickly, and this is also keeping the heat from reaching the second floor. If I choke down the first floor vents and possibly add additional venting to the second floor do you think it will even out the heat? If I add a second vent, should I put it above the valve or the current vent? Am I looking at this correctly?

Thanks,

Mike



      

Brad White

In that first photo

do I see the system feed take-offs coming off between the boiler risers? This is a no-no, encouraging collision of steam and associated free water.



The correct "leaving condition" is to have the outgoing steam to the radiators leave the header, downstream and after the point that both boiler risers combine.  In other words, the basic order of things would be:



1. First boiler riser, starts the header.

2. Second boiler riser tees into the header.

3. First and subsequent out-feeding branches to the radiators

4. Header continues then downturns to form the equalizer and the return connects into this.

Jamie Hall

So far so good...

but how does air get from the steam mains to the dry returns, to get from there to the main vents on the returns at the boiler?  There should be, if I read your setup right, crossover traps from the ends of the steam mains to the dry returns.  These are just like ordinary radiator traps, although they may be one size larger.  If they aren't there, you need to figure out how the air in the mains is getting out!  If they are there, is there a chance they are failed shut?

Jamie Hall

So far so good...

dang double post.  sorry...

Rod

Boiler Piping Problems

Hi- I blew up the pictures of your boiler piping and I agree with Brad, something seems amiss. Having the near boiler piping correct is very important otherwise efficiency suffers greatly.

Edit: Attached is a picture of an excellent Megasteam installation done by two Baltimore steam pros, Frank ("Steamhead")  & Gordon of  All Steamed Up http://www.heatinghelp.com/professional/79/All-Steamed-Up-Inc

Note the dropheader, the high steam risers exiting the boiler and the order of the piping joining the header. This is a perfect example of how it should be done.

- Rod

[Deleted User]

low pressure

Thanks for the reply!

Brad,

The near boiler piping is how you described it. I had a limited amount of space between the first take off and the chimney. To pipe the risers before the header i would have had to change direction and pipe to the back off the boiler and then have them turn 180 into the main. The drops are a nice detail they diagrammed it in the megasteam manual as a "alternate" I wish they would have had it as the preferred.

Jamie,

The returns are piped similar to this diagram, there are not any traps. The main changes to a smaller pipe size and pitches back to the boiler after the last radiator. 



Mike 

[Deleted User]

low pressure

Thanks for the reply!

Brad,

The near boiler piping is how you described it. I had a limited amount of space between the first take off and the chimney. To pipe the risers before the header i would have had to change direction and pipe to the back off the boiler and then have them turn 180 into the main. The drops are a nice detail they diagrammed it in the megasteam manual as a "alternate" I wish they would have had it as the preferred.

Jamie,

The returns are piped similar to this diagram, there are not any traps. The main changes to a smaller pipe size and pitches back to the boiler after the last radiator. 



Mike 

Steamhead

It's still a colliding header

so you have steam and water traveling toward each other. The "alternate" diagram I have shows a drop header (without colliding), which IMHO is the best way to install a boiler with two or more risers.



Here's one way around this problem, on a Columbia I did years ago. Just pipe one riser over so it connects to the header before the steam mains do.

Jamie Hall

How high

is the end of the dry return above the waterline?  Any chance that water is backing out of the boiler and getting high enough up there to block the main vents?  I know, I know, it shouldn't.  But... just a thought.

Rod

Piping Sketch

Hi Mike- I've been looking at your piping and since you have a lot of unions in strategic places, it seems to me that it would be quite easy to modify and get the steam from two boiler risers entering the header properly up stream from the exit risers to the mains.  With a dropheader with its top entry ports, you can drop the header down and get a better lead from the header to the steam mains.  You could also increase the height of the risers coming out of the boiler if you wanted to do so.  As long as the header is above the top of the boiler it is fine. The height of the risers coming out of the boiler is the important thing. (Dan recommends a minimum of 24 inches above the top of the boiler

Leads from header to steam mains - If it provides a better lead and clearance the steam risers ("A" & "B") from the header to the steam mains can be interchanged on ports 3 & 4.  

Having the boiler risers split by the risers to the mains really cuts down the efficiency by producing "wet steam". (See attached drawing)

I've made a sketch which might be of help to you of a possible piping modification . You'll have to check clearances etc. to see if it is even feasible as things like that are hard to tell from a photo.  I think once you get a few minor problems straightened out you'll be really happy. The Megasteam is a great boiler!

- Rod

[Deleted User]

low pressure

Thanks Steamhead, Rod,

I see what you are saying, how important are the drops? My steam is dry and I don't have water hammer.  I can change the piping to the following: See attached.

Am I on the right track for venting?



Thanks,

Mike

Steamhead

The drops

make the header much easier to assemble, and they throw water down to the bottom of the header. If the header itself is 2", as it appears to be, going to 2-1/2" or 3" will give you some amazing steam quality. Here's a shot of this on a Smith G-8 6-section.



What pipe size are your steam mains?

Rod

Drops

Hi Mike- I'm assuming that what you mean by " drops"  is the elbows attached to the boiler riser so that the steam enters the top of the header?   If this is what we are talking about , they are very important. Steam being a gas travels in the upper half of the header and condensate (water) travels on the bottom inside surface of the header. There is a lot of water carried up the boiler risers. (see attached picture of a boiler with glass piping done by Noel Murdough) The whole idea of riser height and the header is to separate out the water and dry the steam. If the entrances to the header are on the bottom or the sides, steam streams collide and interfere with the condensate resulting in "wet steam" being produced.  Besides that, the extra elbows are like a universal joint in a car's drive shaft and provide extra movement really facilitates the fitting of the piping together.

- Rod