Uneven heating

steve_81

Recently replaced an oil boiler with a gas boiler (Weil McLain EG-45) that I believe is properly sized. I have a parallel flow/up-feed, one-pipe system with dry returns. There are 2 mains coming off a 3" header. My dilemma - steam in main A heats all connected load first and THEN, after 20 minutes, steam moves into main B and heats other side of house. How do I get more even heating?

 

I have to manually work the thermostat to get a long enough cycle to heat main B side of house. As a result, radiators on Main A get too much steam and vents begin to gurgle (they are wet) while the other side of the house is warmed only moderately by Main B.

 

Main A – 36 ft

Return A – 41 ft

6 elbows comprise main and return

Main and return both wrapped in fiberglass insulation

6 radiators attached

60 ft of pipe for runs out to radiators

Gorton #4 vents

Pitch is OK

 

Main B – 36 ft

Return B – 33 ft

12 elbows comprise main and return

Main wrapped in fiberglass – no insulation on return

4 radiators attached

40 ft of pipe for runs out to radiators

Mix of Gorton #5 and #6 vents

Pitch is poor

 

Seems like there is a lot more air to move in Main A but steam is drawn to this side. You can also see that return-B is about 2-3' higher than return-A where they come back to the boiler (which I assume could cause a pressure drop difference)

 

Seems the system is out of balance, but why? Is velocity a problem (too many elbows in Main B), is it pressure drop differential due to uneven pitch, is it un-balanced load?

 

 

Mark N

Main Vents

How much main venting do you have on each main? I see what looks like a Gorton 1 in your pictures. You have 2 mains where is the other vent. You will not have balance until you get the main venting straightened out.

steve_81

response

The Gorton 1 on Main A is out of the picture but it is there. Maybe this is the issue. On Main B (that you see in picture) the vent is 8" from the end of the run. On Main A, a Gorton 1 is located 5 feet from the end of the run. I've acutally considered removing the vent on Main A in an attempt to force steam to Main B. Both vents are brand new and unclogged.

Mark N

Main Vents

I would think a single Gorton #1 on each main leaves you under vented. I use 3 #1 on each of my mains. Time how long it takes it takes from when the header gets hot until the main vents get hot. Should be 3 minutes or less. You should be able to balance each main against each other.

Paul48

Bass Ackwards

Don't remove, add vents. Your fast main has more venting.

MTC

Vent those mains FAST

You want the mains to be entirely filled on both sides (IE, extremely low resistance to air movement) before any of the runouts fill up.



Are both mains 2" or 2 1/2"? its hard to tell with insulation. Are they the same size the entire run of the main on both mains, or do they reduce after a while?



If they're both the same size along entire run and the lengths and rad vents are as you list, then B should theoretically be filling first, unless the pitch is really screwing things up. In that case, you may have bigger issues... is it simply missing pipe hangers or something? Is it an easy fix? The additional fittings will add some resistance too, but shouldn't be enough to have the results your describing...



When the main drops into the return, is there a F&T trap, or does steam flow all the way back through the return line? It looks like you don't have a condensate pump, so I'm guessing you have steam all the way back to pressurize the condensate in the return line and put it back into the boiler.



However, your venting would be better served, if possible, at the end of the steam main rather than on the returns. There's really no need to vent out the air in the return, in fact its much better not to if possible. If there's a place at end of steam mains that you could put vents, i'd try them there.



As far as vent sizes, in theory you should need the same amount on each main, assuming they're the same size. For either 2" or 2 1/2" lines, I'd want to see a Gorton #2 or 3 Gorton #1s. If at the end of the return like you have them now, double that. And it will still take longer to heat your system and cost more fuel. Moving them to the end of the steam main would be well worth it if possible. 15" back from the end, or right after the last runout would be ideal, and up 6" or more if possible. Multiple #1s will help if height is an issue.



If it were me and you have the room, I'd try to get a Gorton 2 (or at least a Gorton 1) near the end of each steam main, remove your Gorton 1s from the returns and plug them. Then try the system. If one main is still slower, add a Gorton 1 to that side. You can set up an antler of vents, just use tees with a plug in the end, it will then be easy to pull the plug and add another nipple and tee if needed. Make sure the antler is pitched to drain out any condensate that might get in there...



Also, I'd check on that boiler's specs (don't know off hand) to see if it calls for 2 risers to the header. If you're getting gurgling in your radiator vents, your steam might be too wet, caused by too high velocity through a single riser.

steve_81

@MTC

Both mains 2"' for the entire length.

No F&T trap, no condensate pump

all new pipe around boiler and both returns are new pipe. new vents as well. i don[t believe there is anything clogged anywhere.

Fortunately, at the end of MainB, there is a plugged tee. just for fun (or desperation), i removed the plug and fired the boiler, with no vent or plug installed. I didn't make a bit of difference. Steam is still only going to MainA, and when the load is sufficiently satisifed, steam starts making it way to MainB.

As an aside, when the boiler shuts down and the steam collapses, there is some serious whistle happening in the vents. I'm surprised how much air is being sucked back into the system

Boiler Talk

Scotty, I need more Venting!

My mains are much shorter, but I have 2 equivalent Gorton#1's on each.  It will make a difference and it is pretty easy to do.  Just make sure you have the parts and turn off the boiler before working.  I would also stop insulating with 1/2" insulation.  That's what I think you have, right?  I would order online or find a low cost seller of 1" insulation.  I don't think you will regret getting rid of the 1/2" stuff.  Stop now to save the "could have, should have, would have," like I -----.   

Mark N

Header

Steve I read through your old posts. It looks like you fixed your returns. In the header you are reducing from 3" to 2" between the riser to main A and main B. Smaller pipe has a greater pressure drop. Did everything heat evenly with the old boiler. Have you time how long it takes steam to get to the end of each main?

steve_81

timer

Started timer as soon as i heard air moving through the main vents. After 40 seconds the first elbow at the top of the Main-A riser started to get warm. 30 seconds later, the elbow at the top of Main-B riser got warm. In almost exactly 3 minutes, condensate/steam reached the end of Main-A. Steam/condensate reaches the end of MainB in about 25 minutes. Even when MainB finally gets hot, the radiator at the end of the run is still cold (has about a 5ft run-out and is pitched well.)

it just doesn't seem like steam wants to move through MainB. I beginning to believe pitch is the issue. However, i will take everyone's comments regarding venting into account as well.

steve_81

timer

Started timer as soon as i heard air moving through the main vents. After 40 seconds the first elbow at the top of the Main-A riser started to get warm. 30 seconds later, the elbow at the top of Main-B riser got warm. In almost exactly 3 minutes, condensate/steam reached the end of Main-A. Steam/condensate reaches the end of MainB in about 25 minutes. Even when MainB finally gets hot, the radiator at the end of the run is still cold (has about a 5ft run-out and is pitched well.)

it just doesn't seem like steam wants to move through MainB. I beginning to believe pitch is the issue. However, i will take everyone's comments regarding venting into account as well.

steve_81

timer

Started timer as soon as i heard air moving through the main vents. After 40 seconds the first elbow at the top of the Main-A riser started to get warm. 30 seconds later, the elbow at the top of Main-B riser got warm. In almost exactly 3 minutes, condensate/steam reached the end of Main-A. Steam/condensate reaches the end of MainB in about 25 minutes. Even when MainB finally gets hot, the radiator at the end of the run is still cold (has about a 5ft run-out and is pitched well.)

it just doesn't seem like steam wants to move through MainB. I beginning to believe pitch is the issue. However, i will take everyone's comments regarding venting into account as well.

MTC

It still didn't heat

with an open tee? That's def confusing me...



when you say the pitch is poor... what exactly do you mean? how poor? how so? consistently sloped incorrectly? big dips in the pipe?

BobC

Old boiler work ok?

If the old boiler heated the house ok we have to see what changed when they installed the new boiler. they may have changed the heights of the mains near the boiler.



I would clock the gas meter to be sure the boiler is burning enough gas to support the load. Turn off all the other gas appliances and see how much gas that boiler is consuming.



Add up the EDR of all the radiators and make sure your making enough steam to fill them. If the near boiler piping isn't right that can make getting steam out to the system more difficult.



Assuming the gas consumption is ok go over the mains with a level (do not trust your eye, use a level) to make sure the slope is good, make sure you don't have any dips that might me holding water. You can run a taut length of string underneath to catch any dips after you have verified proper pitch. If the slow main has pitch problems that has to be addressed. It's possible there is debris in that poorly sloped main that is trapping condensate at the bottom of the main and is enough to collapse the steam trying to travel down the main.



Bob

MTC

Pitch

definitely seems to be the biggest concern as of now. If with an open pipe fitting steam is still not making it down that main, there is some obstruction in that pipe. There's really no other solution. Now that obstruction might be nothing more than water, but its acting as an obstruction.



I'm guessing that what you have is a line with a long slow dip in it, creating a condensate water seal (think of a P-trap under your sink). Since you have one pipe steam, once all the radiators have filled and their air vents have sealed. The vents will open and close a number of times as steam condenses in the radiators, until the metal is all hot, then steam condenses much slower. At this point the vents stay closed a lot longer, pressure will start to rise in the system and continue to do so until one of 2 things happens. The pressuretrol or vaporstat kicks off the system, or it has enough pressure built up to finally blow through a water seal and heat the second main.



Question: Do you get water hammer right before/when the 2nd main starts heating? I would expect you'd get some hammer on that line when the seal blows through, if that's what is happening.



Once you figure out what's stopping steam from moving through main B, I'd get your vents moved to the ends of the mains instead of the end of the returns. You've said you at least have a Tee on B already, hopefully there's one on A as well, if not its worth tapping in a 1/2" or 3/4" line for it. Let compressed air push the condensate back into the boiler, not steam. You'll have less water hammer potential, your system will heat faster, and you'll burn less fuel.



But first you have to get that pitch problem sorted out.

MTC

You mentioned whistle...

which vents are whistling on shutdown? Radiator vents or main vents or both? On both mains or just one? A water seal in a pipe could be causing/exasperating this too, depending on where its happening...

steve_81

Old boiler and the pitch

Old boiler sort of worked but it never got enough steam to what is now the hot side of house. There's a castiron baseboard unit that unit sits on MainA and the entire 12' length gets hot now! Never heated with the old boiler.



There was no header on the old boiler. Just a 2" shot straight up to MainB and a side-ways tee to feed MainA within a foot of the top. Equalizer was also incorporated by a tee in the 2" riser. By all estimates, near boiler piping was wrong and I insisted that it be replaced with what you see now. Oil Boiler operated at 82% AFUE andi I averaged about 700 gals per heating season. (800 in first season with no insulation and a very cold winter)



MainB has a lot of elbows. At one section (within 5ft of boiler) the pipe is level. As to the remainder of the run, it's enclosed behind a finished wall so i can't tell if i have dips. That wall will be opened in the spring for some additional renovation work. That's why i'm trying to figure out what's going on so we can fix it when it's open. I'm also adding another run-out on MainB so it will get torn apart. We'll see what's in there.



The condensate water seal argument makes sense. I'll check the gauge to see if there's any increase in pressure as MainB heats. Thing about it though, there is no hammer in the system. Just the wet vents on Main A (and i think it's because there's just too much steam on that side)



Maybe there is debris in that Main, but i doubt it. When we first fired the boiler, the water-level was too high in the boiler and i had horrific hammer. I would think any debris probably got flushed out with all the sloshing in the pipes.



Lastly, the whistling is happening all over the place it seems. Certainly in the return vents and certainly from a few radiators.



Did a few more timing checks. When steam first comes up, i hear both vents venting. First elbow of Main A is hot in 40 secs and first elbow of MainB is hot in 1:10 secs. After that, steam just seems to die in MainB but barrels through MainA. It's actually pretty impressive listening to air being pushed out of MainA vent.



Again, i'll certainly consider vents in the main (as opposed to the returns) but i don't think that's my problem right now.



thanks for all the input, by the way. much appreciated.

MTC

I think you've tapped out my knowledge

without seeing it in person, at least. I'm a bit confused how you get some venting on the B return at startup and then still no heat... maybe someone else has an idea about that.



As far as your wet vents... I don't think you should get any water from the vents on main A, no matter how long they run.



What's your pressure set at? Too high pressure can cause the vents to fail (spit water), as well as cause too wet steam, which causes all sorts of other problems.



I don't know the specs for your boiler, but does it call for only one riser to the header? Many require or at least recommend 2 risers, as this cuts the velocity of the exiting steam in half and reduces how much water it brings with it.