Main Vent Sizing

Brycewvu

I am working to install main vents on my one pipe stems system. I have 3 branches/returns and I am trying to figure out which size main vents I should buy and install. I have measured 2 out of the 3 branches and will be measuring the 3rd this weekend (in the crawl space). Branch B actually comes off the Branch A a few feet up the main header so I included all of the near boiler header pipes in my measurements for both.

I got most of my info from Balancing Steam Systems Using a Vent Capacity Chart (https://heatinghelp.com/assets/documents/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-1.pdf)

1" pipe = .005 cubic feet of air/foot
1.25" pipe = .010 cubic feet of air/foot
1.5" pipe = .014 cubic feet of air/foot
2" pipe = .023 cubic feet of air/foot
2.5" pipe = .030 cubic feet of air/foot

Branch A
3 feet of 2.5" pipe = 0.09 cubic feet of air
22 feet of 2" pipe = 0.506 cubic feet of air
42 feet of 1.25" pipe = 0.42 cubic feet of air
16 feet of 1" pipe = 0.08 cubic feet of air
Total = 1.096 Cubic Feet of Air

Branch B
3 feet of 2.5" pipe = 0.09 cubic feet of air
11 feet of 2" pipe = 0.253 cubic feet of air
20 feet of 1.5" pipe = 0.28 cubic feet of air
25 feet of 1.25" pipe = 0.25 cubic feet of air
16 feet of 1" pipe = 0.08 cubic feet of air
Total = 0.953 Cubic Feet of Air

I am planning to install either Gorton #1 or #2. With those totals, which vents/how many would you recommend? Is my math right? Should these numbers be rounded up? Am I overthinking this?

Also, since I can buy 3 Gorton #1s for the price of a #2, is there a way to get the appropriate venting without having to buy all #2s?

KC_Jones

Just to clarify, you have 1.5", 1.25" and 1" mains? If the pipe is the takeoff to the radiator from the top of the main, it's not counted as part of the main. Confirm that and we can make a recommendation.

As far as Gorton #1 vs #2, 3 Gorton #1 vents are equivalent to the #2 vent, so the cost is a wash, and actually more expensive for the #1 overall because you need fittings to hook 3 up instead of 1. The selection between those 2 usually comes down to how much room you have to fit the vents.

Brycewvu

The 1.5" pipe is a takeoff from that 2" main, but it is 20ft long and feeds 3 takeoffs. The 3rd branch of my steam pipes, which I still have to measure, is also 1.5" and that is likely similar length and also supplies 3 takesoffs. I was treating them as part of the main since they don't directly supply radiators.

The 1.25" pipe would be takeoffs to the raidators. Should I account for this air when I replace the radiator vents instead of as part of the main supply?

The 1" pipe is the dry return. The wet return seems to be incorporated into the near boiler piping and based on recomendations from another one of my posts, I will be installing the main vents off the Ts with a new section of pipe to give me the minimum distance away from the wet return drop. This will prevent me from having to cut and T off on those old return pipes. Here is the discussion link. It has some pictures that will hopefully shed some light on my thought process.https://forum.heatinghelp.com/discussion/194562/steam-main-vent-locations#latest

SteamingatMohawk

Since you mention the Balancing Steam Systems Using a Vent Capacity Chart, you should consider what pressure the system works at and how quickly you want the mains to vent. Then you can go into the capacity numbers to select the proper size.

Additionally, I had a real eye opener, because there is a short article at the end of the report about too much venting . Even though the situation turned out to be because of a Heat Timer valve, the concept is relevant.

@Steamhead recommended to me in one of my conversations to use the 1 oz. pressure for mains and 3 oz. pressure for risers.

If you do the calculations, be sure to include the radiators, especially for the short risers. It could make a difference.

Brycewvu

SteamingatMohawk said:

Since you mention the Balancing Steam Systems Using a Vent Capacity Chart, you should consider what pressure the system works at and how quickly you want the mains to vent. Then you can go into the capacity numbers to select the proper size.

@Steamhead recommended to me in one of my conversations to use the 1 oz. pressure for mains and 3 oz. pressure for risers.

 If you do the calculations, be sure to include the radiators, especially for the short risers. It could make a difference.

How do I determine the pressure that my system runs at? I have a Weil McLain SGO-3. Is it somewhere in the boiler paperwork?

I wasn't 100% sure how to interpret the pressure levels on the charts in that paper.

KC_Jones

The pressure listed on those charts is because some amount of measurable pressure is needed for the instrumentation to have a test. In reality your system starts at zero, so the venting rate is likely even lower than the 1 ounce level.

The main value in the chart, to me, is seeing the comparison of rates between vents to enable one to choose an appropriate vent rate relative to other vents in the system. So basically use the 1 ounce column, but don't worry about pressure as it really doesn't matter. Also, for reference, with a properly sized boiler and proper venting, you really should be running as close to zero as possible, pressure doesn't help and can cause excess fuel usage.

In the case of main vents, just go as big and fast as you can afford, or want to spend. I believe, unless the system is extremely small, there will almost always be a Gorton #2 vent on the system. Now where both mains would need that big is a different scenario, and that is where the venting chart comes in.

So lets say one main is 25' and the other is 12.5', you would want to install about twice the venting on the long main as the short main, so both fill at about the same time.

ethicalpaul

So lets say one main is 25' and the other is 12.5', you would want to install about twice the venting on the long main as the short main, so both fill at about the same time.

I don't find this to be a big concern. If one fills first, almost all the steam will go to the other one (due to it still having an open main vent) before it starts going very far up the radiator takeoffs.

If you try to balance the main vents against each other, you are almost certainly going to force the steam to fill the "easier" one first anyway.

Like if you have a Gorton #2 and a Gorton #1 on two different mains, I'll bet you the #2 one will take all the steam anyway until it closes. Don't sweat it.

dabrakeman

With a little hoofing through your basement when the boiler starts to steam you can easily track the progress of the steam through your mains. They certainly can be balanced.

ethicalpaul

Track, yes. Balance? Maybe. If you have a #2 and a #1 and you find that the #2 fills with steam first are you really going to like uninstall the #2 and what? replace it with two #1s which will actually increase the total time required to fill the mains?

Or uninstall the #1 and install a #2 which will probably just make the smaller main fill up first anyway. Just how much effort is this questionable gain worth?

Edit: sorry, I realize this is off-topic.

Jamie Hall

With regard to the pressure your system operates at -- three things govern that. The venting capacity related to the size of the boiler, the size of the boiler relative to the radiation, and the settings on the pressure control, whatever device you have.

The venting capacity relative to boiler size determines how fast the pressure rises starting from a not boiling condition and in more extreme undervented systems, whether or not the pressure stabilises. The size of the boiler related to the size of the radiation determines whether the boiler pressure actually does stabilize or whether at some point (usually well after all the radiation is hot) the pressure starts to rise again. The settings on the pressure control device determine the maximum and minimum pressure range in which the boiler will operate, provided there is a call for heat.

SteamingatMohawk

Great feedback, I can't help but wonder how relevant the overventing article pertains to real life. I was quite surprised when I read it.

Does anyone have any real life experience with this possibility? The reason I am so interested is that the radiator in the second floor room with the lone thermostat has a fully open Heat Timer and about 6 inches further along the main is the first floor radiator that is not getting as heat as quickly, lagging the others in heating up. Those settings haven't been changed for several years.

I don't recall any such problem in the cold part of the winter, but these balmy fall days are driving me crazy.

SteamingatMohawk

I should also mention there is a Gorton#2 about a foot past the first floor radiator riser (which is also the last radiator along that main) and a Gorton #1 at the end of the return.

SteamingatMohawk

L1 is the first floor living room radiator, L2 is the second floor living room radiator that has the thermostat for the whole house

Gsmith

"Great feedback, I can't help but wonder how relevant the overventing article pertains to real life. I was quite surprised when I read it.

Does anyone have any real life experience with this possibility? The reason I am so interested is that the radiator in the second floor room with the lone thermostat has a fully open Heat Timer and about 6 inches further along the main is the first floor radiator that is not getting as heat as quickly, lagging the others in heating up. Those settings haven't been changed for several years."

Yes overventing RADIATORS can cause problems with balancing. Try replacing the Heat Timer varivalve with some other vent (I like Vent-Rite #1 because they are adjustable). Lots of times balancing problems, like one radiator failing to heat are caused by too much (fast) venting on other radiators and often solved by slowing down the radiators that heat first rather than speeding up the slower heating ones.

SteamingatMohawk

When I did the original calculations, I purposely used the Heat Timer incorrectly thinking having that vent quickly would help with the interface between the radiator and the thermostat, completely ignoring/forgetting about "evenly" vent the radiators. When I went back to do the calculations again with radiator air volumes I realized my mistake.

Although, for the last 4 years no one has complained about the heat once into the heating season, so I have been hesitant to change it.

All that being said, the relevance of my contribution to this conversation is the caution that over venting can happen...with a bunch of extra background for info.

SteamingatMohawk

I use Vent Rite #1s along with a couple of Maid O Mists and the Heat Timer on radiators. Lots of spare vents no longer in service as I have learned how to balance....and keep learning!!!