Main Vent recs

You generally want to vent the mains of a steam system as quickly as you can. A Gorton one will work, just like many others. But a Gorton two will vent three times faster. Yes, I keep the extensions, it can help prevent water from getting to the vent.

The entire time that you have air in your system is time that your boiler is running at full power, but is being restricted because the heat can't get to the radiators. So you have 100% boiler gas usage, but not 100% radiator output, so you lose efficiency. I use gorton 2s, but if you do a full analysis you can determine the cost benefits for your system.

Thanks for the kind words, @PC7060 !

@krmcgee , I'd use the Gorton #2- one on each main. The #1 only vents at half the rate needed to fill the mains with steam in one minute at 1 ounce pressure. The #2 is faster than needed, but that won't hurt.

If you want to vent the mains in one minute at one ounce, the #1s won't do it. See Gerry & Steve's charts.

You could install two #1s on each main, and that would work, but with the extra fittings and labor involved I'd just use #2s.

Running krmcgee's numbers through Gerry and Steve's chart, since this one is easy to settle and it turns out both answers are right.

Thirty feet of 2 in main holds 0.69 cubic feet of air, at 0.023 cu ft per foot.

To clear that in one minute you need 0.69 CFM. A Gorton #1 passes 0.33 CFM at 1 oz, so it is 48% of the rate, which is exactly what Steamhead said. A #2 passes 1.10 and does it in about 38 seconds. Two #1s on a main come to 0.66 CFM, near enough the full minute, which matches his second suggestion too.

To clear it in three minutes, which is the target Gerry and Steve use in their own worked examples in that paper, you only need 0.23 CFM, and a single #1 is 143% of that. Which is ethicalpaul's point.

So it isn't really a disagreement about the vents. It's about how fast you want the main clear, and the vent falls out of that choice. One minute wants a #2, three minutes is comfortable on a #1.

One thing worth checking before buying either, since nobody has raised it: the tapping the vent screws into has its own capacity, and it caps the whole job no matter what hangs off it. An open 1/2 in pipe passes 2.6 CFM at 1 oz. That is not a constraint for you at one vent per main, since a single #2 is 1.1, but it is why stacking three or four vents on a small tapping stops helping. If you ever go that route the tapping is the thing to enlarge, not the vent count.

On the extensions, keep them, for the reason others gave. They hold the vent up away from any water in the main.

AI?