Free tool · One-pipe steam
Gorton #2 main vent calculator
One main, one answer: how many Gorton #2 air eliminators it takes to clear the air in the time you choose, and whether the tapping can carry them.
Direct answer
Count = (main cu ft ÷ target minutes) ÷ #2 CFM, rounded up. A Gorton #2 passes 1.10 / 1.75 / 2.20 CFM at 1 / 2 / 3 oz (Gill & Pajek). 60 ft of 2" main holds about 1.4 cu ft, so clearing it in 2 minutes at 1 oz takes one #2.
One steam main
Schedule 40 air volume ÷ target minutes.
Shorter target = more vents. Mains should vent well before radiators.
Tapping ceiling not published at this pressure
Big Mouth
The judgment call
Main vents are where venting money pays back: steam reaches every radiator at the same moment only if the mains are empty of air first. Adding #2s beyond what the tapping can pass buys nothing, so this tool checks the open-pipe ceiling — on a 1/2" tapping that ceiling is 2.6 CFM at 1 oz, about two #2s. Past that, enlarge the tapping or build an antler manifold.
Long main to the cold side gets #2s; the short main to the warm side can use #1s, per Gorton's placement notes. For several mains, dry returns, and a combined schedule use the full main vent sizer; the walkthrough is in how many Gorton #2. Then balance radiators with the radiator vent speed calculator.
Estimate only
FAQ
How many Gorton #2 do I need?
Divide the main’s air volume by your target minutes to get CFM, then divide by the #2 rating at your pressure (1.10 / 1.75 / 2.20 CFM at 1 / 2 / 3 oz) and round up.
Gorton #1 vs #2 — what is the difference?
Gorton rates the #2 as equal to four #1s. Measured: #1 is 0.33 / 0.54 / 0.70 CFM and #2 is 1.10 / 1.75 / 2.20 CFM at 1 / 2 / 3 oz (Gill & Pajek).
Can I just add more vents to the same tapping?
Only up to the open-pipe capacity of the tapping. An open 1/2" pipe passes 2.6 / 3.4 / 4.8 CFM at 1 / 2 / 3 oz; more vents on it cannot beat that.
Why doesn’t the tool count a Gorton Big Mouth?
No published CFM measurement exists for the Big Mouth — it is not in the 2005 Gill & Pajek chart and Gorton publishes no CFM — so we will not guess one.
Sources
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Need the full worksheet? Open the Main vent sizer.
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