Single-pipe steam main line calculations (3 main loops)

cubicacres

For balancing our main venting, do we need to measure anything past the last radiators? Our setup resembles a shamrock with a single main splitting off twice, making 3 loops total that head back to the boiler room. We'd like to do a good job venting the mains over time as we can afford more main vents. We measured our main lines in the basement for all 3 loops that lead to the 1 inch radiator risers, and here are our measurements so far:

Boiler Risers: 2x3in x33in tall & 26 in long in the drop-header config. =118in total 3in pipe
Header: 4inx48in long, Riser off the Header: 4inx18in =66in total 4in pipe
Combined Main before first split (short & medium/long loop): 162 in total 3.5in pipe
Short loop: 2.5in x 200in + 1.5in x 70 in to last radiator on that line
Med/Long loop shared run: Another 70 in of 3in pipe before the long line breaks away from the med line
Med loop: 3in x 290in + 2in x 220 in to last radiator on that line
Long loop: 2in x 800in to last radiator on that line

Totals:
6 feet 4 inch pipe
14 feet 3.5 inch pipe
40 feet of 3 inch pipe (mostly that medium loop)
17 feet of 2.5 inch pipe (that short loop)
85 feet of 2 inch pipe (mostly that long loop)
6 feet of 1.5 inch pipe

We currently have the following main vents installed:
Short loop: 1 Gorton #2 on a 1/2 inch nipple just after the last radiator 10 feet outside the boiler room (maybe best to add a tree for more here), and 1 plug in the boiler room for expansion here
Medium loop: 1 Gorton #2 & 1 Hoffman #75 inside the boiler room since the last radiator is just outside the boiler room wall
Long loop: 2 Gorton #2's on a 1/2 inch tree just after the last radiator 30 feet outside the boiler room & 1 Hoffman #75 inside the boiler room, and 1 plug in the boiler room for expansion here

With the pipe lengths & diameters and our current vent setup, where would you reccomend we add our next vents to balance out the mains for faster venting? We have another Gorton #2 ready to install now. Gorton mentioned full venting is something like a #2 every 15 feet or so, but are there good reference tables we can check to see what maximum (or at least decent venting until we can buy more over time) looks like for us?

cubicacres

Here's a rough sketch of the mains if that helps (see PDF).

As of right now with our current venting setup, the short loop heats the fastest & gets really hot, followed by the medium loop, and the long loop takes much longer to heat up & isn't as hot when we feel the condensate return pipes back in the boiler room.

Jamie Hall

It really isn't necessary to measure -- or vent -- anything past the last riser on a steam main. Usually that is pretty close to the end anyway -- but not always!

cubicacres

ok-that Hoffman #75 in the boiler room 25 feet past the last radiator & 2 Gortons on on the long loop probably isn't doing much for us, then. Maybe we could remove it & put it with the other vents just beyond the last radiator on one of the lines.

The short loop has about 5 feet of 1.25 inch condensate return after the last radiator outside the boiler room, the medium loop less than 1 foot, but the long loop has about 25 feet before hitting the boiler room.

nicholas bonham-carter

Keep adding Gorton #2's on each dry return, until the back pressure of venting is a couple of ounces, (may need a good low pressure gauge-0-3 psi). You can not have too many vents, but the returns on investment become less as you go above the needed number of vents.--NBC

cubicacres

If I take the estimated "one Gorton #2 per 20 feet of 2inch pipe" suggestion, and try and equalize the 4in/3.5in/3in/2.5in runs with the 2 inch equiv. space in my drawing, it looks like we're about 50% venting from optimal on all 3 loops right now.

My estimate is 2 Gorton #2's on the short, and 4 each on the medium & long loops. Does that seem close per the pipe lengths & diameters I have in the drawing?

cubicacres

As another way to estimate balancing the medium & long loop venting, can we add vents to the long until the condensate return pipe back in the boiler room heats up about as fast as the medium return does? Or is this a false estimate, since the long loop needs to heat that extra 25 feet of 1.25 in condensate return pipe after the last radiator, so it will always be the last to heat up? If this is the case, would we just feel the riser to the last radiator on each loop as another way to estimate balancing if we didn't want to remove the vents?

KC_Jones

cubicacres said:

If I take the estimated "one Gorton #2 per 20 feet of 2inch pipe" suggestion, and try and equalize the 4in/3.5in/3in/2.5in runs with the 2 inch equiv. space in my drawing, it looks like we're about 50% venting from optimal on all 3 loops right now.

My estimate is 2 Gorton #2's on the short, and 4 each on the medium & long loops. Does that seem close per the pipe lengths & diameters I have in the drawing?

Keep in mind with that rule you have to make allowances for the larger pipe. 4" pipe has 4 times the amount of air of a 2" pipe. So using the rule of thumb would dictate a Gorton #2 for every 5' of 4" pipe. I would also suggest that you need to be fairly careful about the main venting because of the splits. The steam will go with the path of least resistance so when you have those splits and vents on the end of either one you don't want one stealing all the steam. I haven't balanced many systems so perhaps a pro who has had to deal with this type of situation could comment. I think you are on the right track with all the measurements. If it was me I would calculate all the volumes for each run, starting and stopping at vent locations and splits. Break it all down into small segments then figure out which sections are being vented where. Might take some time, but should be worth it in the end. Since the main off the boiler actually splits into 3 at some point that initial pipe run is actually being vented from 3 different locations. I think you may need to be a bit delicate to get this one right. This is just my opinion from what I am seeing in your posts.

cubicacres

Thanks. That larger 4 in & 3.5 in pipe just after the boiler before our loops split off does seem to make us need more vents if that air also has to get out for the steam to pass. It seems like we were under-vented historically, with a single Gorton #2 on each loop with the old EGH-85 boiler. Venting the radiator risers sounds interesting as well. Once we save up from the new boiler install, we can try a few more things.

If our boiler is 14% smaller BTU input than our old one & about 4% more efficient with spark ignition & auto vent-damper, is it reasonable to think we could expect an 18% drop in fuel use assuming similar temperatures & run times this year? Adding the Tekmar controller should help us even more, but we'll see what that does.

cubicacres

Attatched is a photo of our long main loop vents-3 Gorton #2's. Since the steam is flowing form left to right in the photo, and they move right to left on this tree/antler, is that a bad thing (conter-flow venting)?

We did this because since it was easy to move the 1/2in riser form the main 180 degrees to get a slope towards the main for each vent rather than use more elbows to give it a slope back to the main as we added the 2nd & 3rd vent. It's pretty tight in there, and we want to adjust the nipples to allow the middle vent to be straight up & down like the others-is this also important to do for proper venting? So far, they seem to all get hot & work, but we noticed one had water in it when they were not sloped to go back to the main.

cubicacres

Here's that photo...

cubicacres

After talking with Gorton about more #2 vents on this long line (that's 15 minutes slower to heat than the medium & short loops), It sounds like we need them to be exactly up & down to have their floats close all the way. This may be why we're not seeing much improvement with the 3rd #2 as shown in the photo above.

Also, with a 1/2 inch tapping, it sounds like adding a 3rd Gorton might not add any value if that 1/2 inch tapping size is limiting us.

How would you recommend increasing the venting with this layout? Adding several 1/2 inch tappings to the 1.25 inch condensate return just after that last radiator riser as shown in the photo? Or increasing that 1/2 inch tapping size to 3/4 or 1 inch? Could we have a 1 inch tapping on a 1.25 inch condensate return pipe? If so, what's the best way to configure several (6-8+?) Gorton #2's on that since they need 1/2 inch connections?