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# How do you Size Steam Main Vent?

Member Posts: 5
I finally got around to measuring the main all the way around the basement. It is ~67' 2". So if I do your calculation I get 1.544841 cubic feet of air.

Now what is the magic to get to the correct Vent size?

Fred

• Member Posts: 5
How do you Size Steam Main Vent?

Hi,

I am looking for information on how to size the Main Vent on a one pipe steam system. I am an amateur home tinkerer. I had fixed most of the other problems by the end of the last heating system but this one remains my last problem I hope.

The system was built in the 20s and has had some modifications. At least two different boilers. (started out life as Coal, then Oil, now Natural Gas). There have been radiators removed and the boiler location has been changed as well as all the radiators have been swapped for Baseboard Steam units against the recommendations of Dans books. ;-)

Unfortunately I inherited this when I purchased the house in 97 not knowing much about steam heating systems. I am trying to resolve two problems at this point. Hi heating bills and one last radiator at the end of the Main that wont heat.

Is there a way to calculate the actual size of the main that should be used? I know that bigger is not always better so I would rather do this the right way rather than guess and guess wrong with other consequences.

Sincerely,

Fred
• Member
Sure is

Measure all of the pipe that the main vent serves. Not the run-outs that the radiator vents serve, just the steam main up to the vent, and the boiler piping. If you have two mains, split the common piping between the two.

2" pipe contains 0.023 cubic feet of air per foot, and other sizes have values, too. If you find out how much pipe and the sizes, we can come up with a volume of air to be vented, and a vent that will do the job.

Noel
• Sizing Main Vent Valves

Based on what you have described your steam heating system is a reasonablly small system.

Sizing a vent valve for a steam main in a building like yours is an excersize that is not needed.

This system is an old one and most probabley had a a master vent on the steam main. The old style vent valve had internal ports of about 3/8".

In buildings like yours operating steam pressures are a major factor.

If your system operates under 2 PSI you can use 2 Gorton # 1 vent valves. each vent valve releases 4 cubic feet of air per minute. The 2 vent valves will release a total of 8 cubic feet of air per minute.

Steam will move pretty quickly down the steam main at that venting rate.

I would not install one master vent as vent valves become defective from time to time.

Two vent valves give you a little bit of redundacy and if one vent becomes defective you still will have air released from the steam main.

The thought that bigger is better or more than a little makes for a better operation does not work in all systems.

The Gorton Vent Valve has internal 1/2" tappins or a 3/4" external tapping.

That allows you to insert the vent directlly into a 3/4" tapped T or install it into a 1/2" tapped T with a nipple.

Make sure that you elevate the vent at 6" above the steam main and about 12" in back of the drop pipe.

Jake

• Member Posts: 5

Thanks for the two quick replies.

I do know that this is a low preasure system < 2lbs.

I also know that it is 2" pipe. I will get the measurements tonight and post back to the wall over the weekend.

There is currently an installed vent that I have to try and get at to remove because it is burried in the ceiling. The current vent let out steam in the past which I know isn't good because then the furnace will never hit the High preasure shutoff thus increasing my fuel bills.

I am not sure at this point if the vent functions at all.

Again thanks for the help so far and as soon as I have more details I will post them!
• Member Posts: 5

Thanks for the two quick replies.

I do know that this is a low preasure system < 2lbs.

I also know that it is 2" pipe. I will get the measurements tonight and post back to the wall over the weekend.

There is currently an installed vent that I have to try and remove because it is burried in the ceiling. The current vent let out steam in the past which I know isn't good because then the furnace will never hit the High preasure shutoff thus increasing my fuel bills.

I am not sure at this point if the vent functions at all.

Again thanks for the help so far and as soon as I have more details I will post them!
• Member Posts: 16,736
Several ways you can go

1.544841 is slightly more than the capacity of the Gorton #1 or Hoffman #75 vent. Both will vent about 1.4 CFM at 2 ounces pressure. So two of these vents, piped together at the end, should work OK.

However, since the main is so long it has more total pressure drop than a shorter main of, say, 3-inch pipe that holds the same amount of air. On such mains, I find that increasing the venting capacity will compensate for this.

Therefore I suggest you use a Gorton #2 vent on this main. It will vent about 5 CFM at 2 ounces pressure, and will compensate for the extra pressure drop in that long main.

If no one in your area handles Gorton vents, go to

www.gorton-valves.com

They can tell you where you can get their vents, and will sell directly to you if no one in your area handles them. Talk to Ken Kunz and tell him I sent you.