1920s Steam System - How to Add Main Vents

if it is a 1 pipe system and there are no vents on the dry return somewhere then it needs vents where those plugs are but the parts of the asbestos that are falling apart need to be dealt with first.

» The amount of venting depends on the size and length of the main

I would rephrase that:

The amount of venting depends on the ability of the boiler to provide steam. When pressure builds up before the main is hot all the way around, then you know you need more venting.

The steam can only go as fast as it heats the main above the boiling point of water.. you need enough venting to accomodate that, and more doesn't help.

What @109A_5 is saying is true in the sense that the main is typically sized for the system, and the boiler is sized for the system, so ideally it comes to the same thing.

A Tee with two vents on it is a good idea in any case because when one fails you'll still have heat everywhere. Below is my setup, with one Gorton and one Maid-o-Mist main vent, and it's plenty for my 2.5" 80-foot-long main. The MoM is a screaming bargain and lets plenty of air out. I went with a Gorton first because that's what all the cool kids get.

cheers -m

This statement is also system dependent.

" The amount of venting depends on the ability of the boiler to provide steam. When pressure builds up before the main is hot all the way around, then you know you need more venting. "

My system never goes over 2 inches of water column regardless if the main vent is used or valved off. The predominant benefit (main vent versus no (or poor) main venting) is with a hot main the steam will propagate faster, purging the air out as fast as possible, filling the main with steam as fast as possible.

You want enough venting so when the mains are hot the steam will fill the main as fast as possible. There is a point of diminishing returns. Since even with a hot main the steam will only move so fast.

The "main". Start with the pipe coming straight up from the T on the side of the boiler in the first picture. That's the beginning of your main, and it remains a main all around the basement until you get to the very last radiator takeoff. It may split, in which case you now have two mains…

And it needs to be vented, which can be done anywhere after the last radiator takeoff and before it drops to the boiler.

Now it looks as though you have at least two drops — they're also in that first picture — and it looks as though one of them may have a pipe from a near floor level pipe, which probably picks up a drop somewhere else in the basement. Problem. Those to drops join above the water line, and that may give some problems. Have to see more to know.

Problem number two: the insulation on those pipes has asbestos…

This would have been ok on the original boiler with a water line that was above this point, it is not ok with this boiler where it is now above the water line as @Jamie Hall said.

I thought i was looking at a mirror for a moment until I relaized there were 2 boilers.

Those are probably dry returns/main extensions and those plugs are probably where the main vents were. Without main vents you will have the problem that having the returns connect above the water line causes all the time, namely that the air can't get out of one (or in this case both) of the mains.

That asbestos looks like it would come loose if you tried to wrap it in something.

Unless there are presently vents at the far end of the mains, the vents could be added here.

you can use some 45's to offset it and bring it up straight next to an obstruction. the bigger issue seems to be that it appears to be embedded in asbestos lagging.