Main vent sizing thoughts

I often see people using the size of the mains and how long they are to determine main vent sizing and quantity.

I feel this is incorrect and the only real factor is the size of the boiler. The boiler is what determines how much volume is available to push air out.

My reasoning is the only thing driving the air out of the mains is the boiler and this stays fairly constant regardless of the piping size and length. If you take an EG-40 and install it in 100 different houses with all different piping configurations, it's going to produce the same amount of steam regardless. If the piping is cool, the vents could be much, much smaller and obviously larger piping will take longer to heat, but this shouldn't be considered when sizing.

On very cold nights, where the system runs a lot there may be times the off time is very short and the system needs to still vent freely. The piping it self becomes almost invisible because it doesn't cool and the steam doesn't need to heat much, it just shoots down the pipe. The other night, my system from the time the thermostat called for heat, the time the damper took to open and the burner to light, got steam to the end of the 29' main in 65 seconds. If I had less venting, that would have taken longer, produced more noise from radiator vents, and possibly threw the system balance off a bit for that cycle.

I feel main venting should be sized 100% based on boiler size. If a small system has a grossly oversized boiler this becomes even more important because the last thing you want to do is keep the steam from getting to the radiators with an oversized boiler. The bigger the head start the system gets to cope with the excess steam production, the better.

On an EG-40 I currently have 5 Gorton #1's on a 29' 2" main and a single Gorton 1 on a short 11' 2" main. They're different because I needed to delay the short main quite a bit to keep things timed the same. So, in my case 6 Gorton #1's for an EG-40. Some would say this is too much, but I feel it's maybe 1 too many at best.

Not sure if it works this way yet, but that gives me roughly 17,000 btu/h per Gorton #1 going by the boiler's gross output rating of 104,000. I feel a number of 17,000-21,000 btu/h per G1 is probably a really good bet.

A boiler with a gross output of 150,000 would need 8 to 9 Gorton #1's divided in whatever way is needed to balance the mains. If a main tends to hog the steam early on, it needs to get less venting and the extra can be shifted to the slower side(s) of the system.

Just wanted to share that. Maybe it'll help. I only used Gorton #1's because it's what I've worked with, I have nothing against other brands.