Steam main venting location and sizing

BigErl

I’m looking to upgrade the main venting for a boiler I just installed but I’m not sure how to distribute the vents.  A 4” main comes off the boiler, goes for 65’ then drops into the wet return and there is venting at the end of it.  About a foot before the end of this 4” main, a 3” main branches off and goes for 116’ feet around the rest of the basement back to the boiler and drops into the return and there is venting at the end of it.  I included a diagram.  Can I treat these as 2 different mains and size the venting for the 4” portion and install it at the end of it (vent A) and then size the venting for the 3” portion and install it at the end of it (vent ?  Or should all the venting be installed at the end (vent with just a small vent (vent A) for the 1’ section of 4” main after the 3” main branches off?

KC_Jones

With that much piping I'd go with your plan of venting for the 4", then the 3". You are going to need a whole lot of vents for that application. Double digit quantities of Gorton #2 vents are in your future.

BigErl

Thanks for the reply. Not sure why I ended up with sunglasses emoji in my post. 

Steamhead

You want all your venting at the very end of the main. Depending on the venting pressure (1-3 ounces) you might need 6-10 Gorton #2 vents.

What size vent pipe do you have at the end of the 3"? Usually it's 3/4" but I've seen larger.

If there are no radiators connected to that 1" line that comes off the 4", I wouldn't bother to vent it. Why fill it with steam if it doesn't feed radiators?

BigErl

The end of the 3” main is bushed down to to 3/4” for the vent. If I take out the bushing I’ll have a 2” port.  

KC_Jones

According to the Gill/Pajek chart a 3/4" pipe will only support ~4 Gorton #2 vents. A 1" pipe will support about 5 vents. Given the quantity of venting you need I'd say you will need to pull that bushing and get to a larger pipe size.

ethicalpaul

I'm a little curious just because of the size of the mains...what is the capacity in net sq ft of steam of that boiler?

BigErl

I don’t have the chart In front of me but it’s a Weil McLain LGB 4.  Using the 2 oz column in the Gill/Pajek chart I come up with 7 Gorton #2 vents. The 1 oz column gives me just under 11 Gorton #2 vents.  Does anybody have any thoughts on how many I should use and what size pipe I need to install them on?  I’m leaning towards using 7 Gorton #2’s. 

ethicalpaul

See KC's comment just above mine, but if it were me, I'd start out conservatively with 5 #2 on a 1" pipe and time it to test how it does. I feel the theoretical charts tend to overestimate the steam flow. The steam has to warm the pipe as it goes and that slows the steam considerably. But this size of boiler is outside of my area of experience.

But you can always add more so why not try some and test?

BigErl

Thanks for the replies. I went with 7 Gorton #2 vents on an 1 1/4” manifold.  First floor radiator vents are no longer spitting.

ethicalpaul

Go big or go home