Main line balancing ideas

cubicacres

Steamhead wisely mentioned we could split our long (20 feet longer & just a 2 inch pipe) basement main line loop with 9 radiators on it into 2 loops to better balance with the short line (3.5 inch pipe) with 6 radiators & medium line (3 inch pipe) with 7 radiators on it. Unfortunatley our longest line is also the smallest diameter pipe & has the most radiators on it :-( Did that happen from the coal days when everthing evetually got hot enough to satisfy even the farthest radiators on the smaller main supply lines?

Since we haven't split the long main loop yet, do you think we'd see some benefit to swapping a hoffman #75 vent from the long line with the gorton #2 from the short line to push the steam to that longer, smaller line with more radiator load? We have hoffman 1A adjustable vents on all radiators (levels 1-5 for most rads with 2-3 being the most common setting) other than the last 3 on the long line, which are larger gorton rad vents to favor that long line, along with 4 gorton #2s & 1 Hoffman #75 on the long main line as well. Any other suggestions, or are we at the limit of what venting or anything else can do short of re-arranging the main?

Fred

You've got 4 Gorton #2's and a Hoffman 75 on the long main. I assume they on an antler? If so, what size is the Tapping/pipe out of the Main? If it's only 1/2" That pipe will only vent at a rate equal to two Gorton #2's. If it's 3/4" or 1", you are fine.

MilanD

I would slow down venting on the faster/wider loop even more by replacing the main air vent with one that's slower. Same on rads. Then, the smaller pipe main, put one or two gordon 2 or a few of them (start with 1), and made-o-mists on those rads.... then play with balancing. From. Dan's book made-o-mists have the fastest vent rate. Also, made right here in the USA.

Fred

You want to vent mains as quickly as possible. Vent rads slowly, and increase the venting on any of the rads further away and/or the largest rads only after you get the mains vented properly. Don't slow the long main down, speed the slow mains up, if anything. Do they need more venting? Slowing that long main down is likely to start to push steam out to the rads connected to that main, especially if you put larger vents on those rads. Again, I suspect the limitation may well be the vent tapping and/or vent pipe coming off of the Main(s). What size are they?

cubicacres

2 antlers on the long main, one 1/2 inch tap with 2 gortons, one 1 inch tap with 4 gortons & 1 Hoffman, but only counting 2 since 2 gortons are downhill on the "T or bar" style antler and need to be re-arranged to work in our opinion. The short main has one gorton currently with a 1/2 inch tapping directly from the main.

I'll check the main and see if the main tap under the antler is 1 inch or 1/2 inch for our 4 gorton & 1 hoffman antler tree, and if the tap were 1/2 inch by chance, does this limit the rate to about 2 gortons no matter if the antler is 1 inch or not? If we just have 2 1/2 inch taps leading to 1/2 inch or 1 inch antlers that are functionally limited to the narrowest 1/2 inch dimension, do we need to drill another 1/2 inch or larger tap on that long 2 inch main, or can we use the 4 gortons & 1 hoffman on a 1 inch antler off a 1/2 inch tapping?

Fred, did you mean short instead of long in: "Don't slow the long main down, speed the slow mains up, if anything. Slowing that long main down is likely to start to push steam out to the rads connected to that main, especially if you put larger vents on those rads."?

Fred

@cubicacres , my comment was related to the statement that MilanD made about slowing the fast main down. You don't want to do that. You need to speed the slow mains up.
To answer your question, yes, you are limited to the size of the tapping in the main. If it 1/2", two Gortons or one Bigmouth and maybe a Hoffman 75 is about all you can vent. The 1' antler won't help. If I were you, I would determine, based on main length and pipe size, how much air you need to vent and then install enough vents to accommodate that. To contunue to just add vents isn't the best approach.

cubicacres

Thnaks-I'll measure the length of pipe from the boiler and track the reduction in size of the long main to find the estimated venting needs next.
I took 2 photos that show the 2 tappings:


It looks like the first is a 1.25 inch T pipe section with 1/2 inch antler pipes and 2 gorton #2s, the second tapping behind it is 1.25 inch T pipe section immediatley reduced to 1 inch pipe & 1 inch antler pipe and has 4 gorton #2's (2 are down-slope, so I imagine not venting very well) & 1 Hoffman #75 on it currently.

Fred

Those tappings should and that antler should support all those vents. It looks like a LOT of vents. That should be more than enough unless you have a very, very long main.

cubicacres

So I measured the mains today (see PDF of my calculations). All 3 loops share the near-boiler riser, header and first run of pipe until they split off, so I'm wondering if I count that near-boiler piping in all 3 loop measurements, or just one, or ignore it? (I suspect all 3, but not sure).

Long loop: 6ft of 3.5in riser from boiler, 3ft of 4in header pipe, 14 ft of 3.5in main, 6 ft of 3in main, 58 ft of 2in main until the 6 gorton (2 down-pitch) & 1 hoffman #75 vents, with another hoffman #75 in the boiler room about 40 feet past the other vents-not doing much good in my opinion since way past the last radiator. This calculates out from the charts with: 3.322cu/ft on 87 feet of pipe.

Medium loop: 6ft of 3.5in riser from boiler, 3ft of 4in header pipe, 14 ft of 3.5in main, 24ft of 3in main, 23ft of 2in main, 6ft of 1.25 in main until 1 gorton #2 & 1 hoffman #75 vents. This calculates out from the charts with: 3.531 cu/ft on 76 feet of pipe.

Short loop: 6ft of 3.5in riser from boiler, 3ft of 4in header pipe, 14 ft of 3.5in main, 18ft of 2.5in main, 6ft of 1.5 in main until 1 gorton #2 vent. This calculates out from the charts with: 2.294 cu/ft on 47 feet of pipe.

Assuming the venting chart calulations are correct and I used the near-boiler piping with each of the 3 loops, it looks like the medium loop actually needs the most venting. Interestingly, we noticed the short & medium loops heat up the condensate pipes back in the boiler room in under 10 minutes, while the long loop doesn't get hot in the boiler room and takes 20-25 minutes to heat up just after the vents, still 40 feet ahead of the boiler room. The long loop does have a few more radiators on it than the medium loop. Any thoughts on what we have going on here?

Fred

@cubicacres , The reason those pipes don't get hot past the vents is that you are only veting air out of the pipes up to where the vents are located. There is no need to vent air out of the dry returns. They will eventually get a little warm, past the vents but getting the air out of the pipes just past your last radiator run out is the goal. If you want an accurate time for the mains to fill with steam, time it from the time the header gets hot to the time you hear the vents close.

cubicacres

Thanks. Would you suggest removing & plugging that last Hoffman #75 on the long loop main in the boiler room since it's 40 feet past the other vents as pictured above and may not be doing any good venting the last 40 feet of return pipe? Adding it to the other vent area or another (medium or short) main loop maybe?

The medium loop is slightly larger than the long loop per the measurement I made (surprising to me, but with more smaller pipe diameter makes sense), but the long loop has 3-4 more radiators on it than the medium loop, is mostly a 2in pipe instead of the 3 in pipe for the medium loop, and branches off the medium loop at the top of the pipe, whereas the medium loop continues straight ahead down the line without branching away and may get more steam with the more direct route of the pipes? Any thoughts on balancing this out to get the long line heating faster short of moving the pipes around?

nicholas bonham-carter

Have you tried measuring the back-pressure during the venting phase? My six dry returns with multiple Gorton 2's on each are releasing the air with only a couple of ounces of resistance, and you should aim for that.--NBC

Steamhead

I've looked at this system. The pipe sizes are key here. That 2-inch main has much more resistance per foot than the larger mains do, and it has more radiation. All the venting in the world won't help if the pipe is that much smaller relative to the other two. The steam will go where the resistance is less.

If this were in Baltimore rather than Milwaukee, I'm sure it would be fixed by now

cubicacres

Thanks...I wish we lived closer to Baltimore :-)

Fred

Sounds like your best bet is to split that long 2" Main @cubicacres . If you're going to spend time and money trying to fix a problem, that time and money should probably go where you'll get the best bang for the buck.

cubicacres

Alright, we'll focus on getting the cash together for that job. When we create the new loop, can we join the new condensate return piping to another loop or does it need to go all the way to the boiler with its own wet return?

Steamhead

All the return lines have to join together below the boiler's waterline.

Fred

Doesn't have to go all the way back to the boiler but as Steamhead says, needs to be joined together below the water line

Steamhead

On that job, most of the returns are dry until they enter the boiler room, then the drop. The new one will have to do the same thing.

MilanD

@cubicacres

Just curious: did you ever fire the boiler with the vent completely removed from at least the smallest diameter pipe that heats the slowest? As in, leave just your 3/4 t open, to measure the time it takes for steam to get to it all else equal?

This is what I meant by balancing venting: to get steam to push equally towards rads on smaller diameter pipe and not take 20 min, by slow venting on larger pipe. Stam will still go there, but more will now go to smaller pipe, as it will have larger venting capacity when compared to other pipes. This should slow down the speed with which steam gets to larger pipe, sure, but speed up the steam to smaller pipe, and instead waiting 20 min, you may now get to 15, or 10, while the other pipes and may now also take 10 or 15 min, which will in essence, balance your mains.

As it was mentioned above, steam will travel the path of least resistance. In your case, and if I understand your situation correctly, under equal venting conditions, steam will travel where it's easiest to go first (largest diameter pipe with best venting, in theory, as if you were to remove all main vents). Also, pipe will only vent as fast as the capacity sum of all its openeings (main plus sum of all rads) without any vents, and no faster. One of Dan's book has venting capacities at 1,2,3 oz of pressure on open 3/4 pipe, and on various rad and main vents. 3/4 pipe or t can only vent so fast, so having 5 Gordon#2 may be an overkill (as in sum of 5 gordon 2s may be larger than venting capacity of the 3/4 opening itself). At the same time, having 3 may be good, if you then try to vent the smalles diameter pipe as fast as it can vent, reaching speed of what it would vent if it had just the opening without the vent there. As you are trying to balance the system, you want all your runs to get warm at the same time. Thus, play with that thought and see how you can best achieve it under current conditions. Repiping, unless you do it yourself, can be quite pricy.

Remember also that rad vents help evacuate air as well as the main vent, and once main line is filled with steam, it will again push up to rads, but faster to rads with larger venting capacities. Also, steam will not bypass the first rad on the zone/loop, while rushing to the main vent at the end of it. It will go up to that rad too and how fast will depend on rad vent: aforementioned book shows hoffman 40 having, if I recall it correctly, something like 1/3 venting rate of made-o-mist with D orifice. This means if you also vent rads that are closer to the boiler with slower vents, more steam will be pushed down the line, getting you closer to balance: last rad getting as hot as fast as possible.

One final thought: look into trvs: thermostatic rad vents for a few rads at the beginning of each loop. These will act as a mini zone for each rad. Once room is warm, it will close and not let any more steam come in, pushing the rest of the steam up the loop, which will cause the subsequent rads to also heat up quicker.

Yes, there are friction losses to consider, but at ounces of pressure, this is negligible if all your rads and mains are venting. Think of it as a spider web, with the boiler in the middle. It will take more time for steam to get to the outer edge of the web, all else equal, unless you put some barrier on certain pathways to force flow in the other direction. Venting does this, on the mains and on the rads.

I manage a 10k sq ft building with 790k btu lgb7 boiler and 3 zones: 2 x 2.5 inch loop that are some 190 feet long and a 2 inch loop that is also some 160 feet. (Note: at the end of each run and after the last rad, pipes size drops to 1.25 inch goes to ft and t traps combo, and then drops into a 50 gal condensate tank.) Rads are also connected with different diameter pipes: 2rd floor auditorium with 1.5 inch pipe risers from the main. 1st floor auditorium off 1.25 inch pipe risers, and the 2 inch loop with 1 inch pipe risers to rads. Vents on them vary from Hoffman 40s to made-o-mists with various orifices on 2.5 inch lines, and made o mists and trv valves on 2 inch loop, with trvs on first 5 rads in the run.

Using what I described above I am getting all 3 loops to heat up at the same time: combo of main venting, thermostatic rad vents and larger orifice valves on rads farthest on the zone/loop. It took some trial and error, but it's done.

Entire system is hot in about 20 min after steam starts to cook, and once it's fully cooking and all rads are hot, it shuts off at 7 oz of pressure on a vaporstat.

cubicacres

Ok, since the 3 current returns are dry until they drop next to the boiler to go below the water line, I guess that means breaking a few cinder blocks to get the new 4th return all the way back to the boiler with the others, rather than just join it up 20 feet outside the boiler room to another dry return, then. We were hoping to make it easier, but if the return has to join the others below the water line, it needs to be back in the boiler room.

We did time the steam with the open 2 inch pipe when we first put on the 3/4 in antler (with 2 Gorton #2's) & 1 in antler (with 4 Gorton #2's) vents on that long loop-it took about 4 minutes from the header getting hot if I remember correctly, so about 6 minutes form initial firing? In any case, we were impressed that it was under 10 minutes. We used Dan & Mr. Gill's venting charts to maximize the venting per pipe diameter. We noticed the time getting better (now about 13 minutes later to heat that long loop) as we changed the Tekmar 279 boiler control settings & swapped the Hoffman #75 for a Gorton #2 on the long loop & put that Hoffman #75 on the short main, along with adding 2 larger Gorton radiator vents to the last rads on the long line. Balancing the mains by bringing the times closer together seems to be working. Ideally we'd speed them all up instead of slowing one down a little to speed the slowest one up, but I suppose it's better to have them all closer than one far behind. Nice to know balancing can be done for longer lines with pipe similar in diameter to our system.

MilanD

Just out of curiosity - question for the expert people here on the wall: why exactly can't they return the new 4th zone into one of the existing runs? Is it that there would now be more condensate than one pipe would be able to handle if it was tapped into? I'm not quite getting the logic behind it other than if there is NOT enough run from the last radiator on the zone that's tapped into to the boiler. But if there is enough space and run and it shows it is able to hold the extra condensate, couldn't it then be done? No?

Steamhead

Because steam could travel from one return into another. The key is that they must all drop below the waterline. This means that water is standing in each drop before all the drops connect together, which keeps steam from traveling between return lines and possibly causing banging.

MilanD

Got it. How about doing an FT trap? Or even some kind of plumbing p trap to separate the two with a water plug?

JUGHNE

The wet return section at the boiler does just that, create the plumbing water trap. You might say each return has different pressure in it and by holding the end of the pipe under enough vertical water the pressures cannot pass from one to the other because of the weight of the water column.

I believe an F&T would just complicate life for your and your system.

MilanD

So, in theory, when joining a new loop (zone) into an old one, instead of going to the boiler and joining them all there under water (to save on costs, breaking walls, extra piping, etc), one could make, say, 3 ft vertical drop and rise in that new 4th zone somewhere by a wall and out of the way (essentially making a tall p trap) , creating a water plug with enough static pressure (3 ft water column = 1.3 psi) to not allow steam from the other line which it's joining (that line would have 6-9 oz pressure, ideally) , to back into it. No?

I'm just thinking of practical application. This is not my system, but am wondering if @cubicacres can save some costs by not having to repipe wet returns by the boiler and break-up the walls in order to run that 4th zone.

As I'm thinking about it, I can't see why this wouldn't work... Sure, it's unusual, but - there is a main vent at the end of new zone, then reduce size of the pipe and drop it 3 ft down, bring it back up slightly below the other side, and then join that into the existing return, prior to it going into wet return. Pitch will have to be watched to make it possible. I am just wondering if there are any other considerations that wouldn't allow for this... tall p trap will separate the steam from 2 lines. It may have to be manually filled before staring up for the 1st time (with a hose and through the vent opening on the main), and there you go. This would be a heck of a lot easier to pipe in...

JUGHNE

I wonder if the new and old returns need to be dropped into a wet loop and then use the existing dry return to drain them both. Main venting for each main would have to be before the wet loop.

I believe in a previous post this solved a problem when new boiler didn't get raised up on 4" blocks. That may have been a wet return that turned into a dry return?? Someone may remember.


This is getting above my pay grade and experience. Perhaps more input will be applied.

cubicacres

Thanks for the great discussion. I can visualize the need to have them join up by the boiler and sink into the water to prevent steam form moving around the condensate lines & possibly run up another zone backwards f the slight pitch is all that's keeping the condensate flowing downhill back to the boiler. The closer drop would need to be overcome to return it to the boiler room, so maybe breaking out some more of the boiler room wall is needed in any case.

I think a 1 inch condensate line was reccomended with the loop/zone split, but the other lines are 1.25inch, does that matter much? Related to that, if the long zone/loop is 2 inch pipe, the same 2 inch pipe or would a slightly larger/smaller pipe size such as 2.5in have any use for the new zone?

MilanD

Above my pay grade...

cubicacres said:

I think a 1 inch condensate line was recommended with the loop/zone split, but the other lines are 1.25inch, does that matter much? Related to that, if the long zone/loop is 2 inch pipe, the same 2 inch pipe or would a slightly larger/smaller pipe size such as 2.5in have any use for the new zone?

That said, and for the sake of discussion, here's something from observing our 3-zone system.

We have 3x ~180 ft loops: 2 zones are 2.5 inch pipe and 3rd zone is 2 inch. It is on a 10,000 sq ft building with 2 big halls (15+ ft ceilings, and 15+ ft cathedral ceilings) with 7-8 bigger rads in each (one is 7 other 8). These 2 halls are each on it's own 2.5 inch zone/loop, and then the 3rd zone for 'house' loop are 2 inch pipes.

Interesting part on rad risers piping:

On the 2 zones feeding the halls (each on its own 2.5 inch main):
- 2nd floor hall - rad connection is 1,5 inch pipe.
- 1st floor zone rad connection is 1.25 inch pipe.

3rd zone on 2 inch pipe:
- rads on 2nd floor are 1.25 inch pipe,
- and 1st floor are all 1 inch.

All dry returns piping after the last rad reduces: 2.5 inch to 2 inch, and 2 inch to 1.5.

So, depending on how far the rads are, how large are riser pipes to rads, and how many rads will be on the new zone (EDR), if similar to the first 2 zones, keep same diameter pipe ratio. If less EDR, you can reduce pipe size. As to dry returns, it would probably be ok to reduce them just like the other ones, same ratio. Afterall, steam condensate is 1,700 times less volume.

With what I described, our system is balanced in such a way that when all the zones come on, every last rad on each heats up approximately at the same time.

One last note - we have zone valves. I only shut down one zone in the hall that's used only 2-3 times a week. I have noticed that our Weil-McLane LGB7 (790,000 BTU), gets to high-pressure limit (7-8 oz vapor) much quicker when that large zone is closed. Closing off the zone simulates oversized boiler. I also noticed that the boiler would then cycle on pressure much sooner, and longer, in this scenario (while the stat is still calling for heat). Alos, pressure would build and vaporstat would shut off the boiler, but the last rad on our 2 inch line would still not be hot. I don't know if you will be zoning all this with a zone valve or not, but what ever you do, make sure you vent the heck out of that new zone.

MilanD

BTW, I really think you can do the pipe dip thing for the new loop/zone and not have to pipe all the way into boiler room. See this post and this discussion on 2 pipe vacuum vapor system (anything under 1psi is vapor, I guess). It utilizes the large pipe dip to create a separation from supply and return. As long as our op pressure is under what the water column pressure is, you should be good.

Dadministrator said:

Here's the entire thread. Quite interesting.

http://forum.heatinghelp.com/discussion/160143/two-pipe-steam-no-vents-no-traps

Cheers!

cubicacres

Thanks, we have lots of Gorton #2 vents, so we can use them on each new zone after the split for max venting.

And thanks for the drawing-would that apply to our single-pipe system, or just dual-pipe?

MilanD

My comment earlier stipulated that if you have room, from new zone at the ceiling level to floor in your basement, to run a big 4-5 foot piped "u", essentially a p trap, you could then join it back into an existing dry return and not have to pipe that new zone all the way to boiler and create a separate wet return, having to break wall, and repipe all the wet returns to receive the new zone return. You just have to make sure water column creates greater hydrostatic pressure than the system operating pressure. Otherwise, operating pressure will blow the watern out of the piped "u", rendering it useless.

cubicacres

Would that P trap keep the condensate water in the trap instead of letting it flow back to the boiler for re-use (at least some until it overflowed on each side of the trap)?

MilanD

Correct. You could just fill it with water prior to firing the boiler, with a hose. You can pipe a tee above it with a capped nipple to use for this purpose. Voila, an instant p trap. As the condensate returns it would act exactly like a regular plumbing drain, except for the boiler return. Key is it be tall enough to have a hydrostatic pressure greater than system operating pressure, and that everything is pitched correctly.

I would also pipe at least one tee with a drain at the bottom of the "trap", to be able to flush it from time to time. Just like a regular p trap, it will also trap dirt, rust and whatever else would drain into it. You can add a dead leg on one or both sides on the bottom verticals too, with a regular ball valve on them. Would make for an easy draining and cleaning.

If you decide to do this, do write up a maintenance manual and leave it attached to the contraption. One day, when someone else lives there, it will explain what's going on.

MilanD

One more note: by repiping existing main into 2, you will add some edr through new pipes. Just make sure there is enough capacity in current wet returns to handle any extra condensate.

Steamhead

MilanD, I've seen this job- not sure there's a good place for a water seal there, or that building one would take less effort than running the return back to the boiler.

MilanD

Thanks @Steamhead. Only thinking of possible easier solutions on installers and home owners.

Not much relevant here, but along the same lines: I haven't seen anyone with this yet on the wall, so here's a -- false wet return. I guess, for 2 pipe system where that return is preferred to be wet?

Check it out! Those dead guys were smart...

cubicacres

Interesting...would that equalizing pipe be open, but allow steam to pass & down the upper main line while allowing the condensate to return with the proper pitch? I'm not as familiar with the air valve operation on it, though.

MilanD

Yeah, I'm not really sure either. The accompanying text said this can be utilized in a 2 pipe system.