How Many Main Vents

CommAve

I'm new today and should have put the following in Strictly Steam

Hi,
I'm trying to balance out a single zone, steam heat, 5 story (plus full basement) apartment building and I'm replacing many of the radiator valves in order to do so. The front of the building is about 100 feet from the boiler and always under heated.

The distance from the boiler to the two furtherest risers is about 100 feet and the main is 6 inches.

Is a single Gorton #2 or Hoffman 75 on each main sufficient ? If not, how many vents should I have at the end of the two mains, before the risers ?

Thank you.

baj702

I'm no expert, but I had to do the same thing. Here's some info I put together.

Here's the venting capacity of various vents and pipe sizes for comparison:
1 inch pipe: 11 CFM @ 3oz
¾ inch pipe: 9.5 CFM @ 3 oz
½ inch pipe: 4.8 CFM @ 3 oz
1/8 inch pipe: 2.5 CFM @ 3oz
F&T trap at condensate tank (Hoffman FT015H): 0.966 CFM @ 3oz
Barnes & Jones Bigmouth (@2): 3.6 CFM @ 3oz
Gorton #2: 2.2 CFM @ 3oz
Gorton #2: 1.75 CFM @ 2oz
Gorton #2: 1.1 CFM @ 1oz

A 6" diameter pipe holds .20 cubic feet per foot length. So, for exampe, if you have 100' then that would be 100*.20 = 20 cubic feet.

A Gorton #2 will vent 2.2 cubic feet/minute at 3oz pressure (about the same as 1/8 pipe for comparison), so it would take about 9 minutes to vent (at 3psi). If you installed two then you could vent it twice as fast.

1. Air will start getting pushed out the vents as pressure builds, as in from 0 psi to 3 psi. So most of the venting will be at lower psi. By the time you get to 3 psi all the air should be out already.
2. https://heatinghelp.com/systems-help-center/balancing-steam-systems-using-a-vent-capacity-chart/
3. For comparisons, I have a 5" main with about 200ft of pipe. I have 2 Gorton #2's and 2 Barnes and Jones Bigmouths + radiator vents + an F&T trap at the end.