Venting a steam condensate return line

Tad Wysor_2

Somewhere in the past somebody added a new loop to our old Victorian house's one-pipe steam system to heat an addition. Just as the condensate return line drops to the boiler level, they put in a 1/4 inch fitting and a regular radiator vent. Now, it hisses all the time, and it's probably the place we're losing the most water out of the system. It's inside a wall that I've had to open up, but still hard to get to. (The other 3 circuits have big, relativly new vents at the points where the return lines drop to boiler level.)

My questions for anybody who's listening: 1) What is the purpose of return line vents? (Maybe keeping an escape route for the steam in the line so it doesn't block the returning condensate?) 2) Do these vents work like the radiator vents in the house, so they thermostatically shut off when steam hits them? (If not, seems that a radiator vent on this hissing line is the wrong hardware in the first place). 3) If my solution to the hissing/loss of water is to substitute a "normal" return line vent, I presume I'll need an adapter to connect the quarter-inch vent fitting to a half-inch vent coupling. Do such adapters exist, or will I likely have to (gulp!) cut the pipe and put in a half-inch fitting for the new vent? THANKS

bob young

access

sounds like the vent is defective & needs to be replaced. all vents should be 100% accessable. install an access panel or door. simple job.

Christian Egli_2

Walling up a live vent - what a horror

The air outlet at the end of the return makes some sense, but it is not necessarily needed. What is needed is a place for air to get out at the end of the radiator - just like on any plain one pipe radiator. What happens further down the return line doesn't much matter whether or not we can get steam in there or not. The condensate will flow through air.

So, in your walled up case, if you have a good accessible vent at the end of the radiators draining into this line, you'd probably be ok with a plug here in the wall.

If your branch radiation depends only on this vent for proper breathing, then you need to keep it or move it.

Next

Since you mention there is a lot of spitting, and you mention what seems to indicate this vent is near the boiler water line, I think you'll need to measure your A dimension. If the vent is below this dimension, replacing it with a plug is necessary - and you'd have to make sure the branch radiator is not left unvented.

Steamhead (in transit)

Those return line vents

are probably what the installer used to vent air from the steam mains. If the return lines to the venting points are fairly short, this placement is OK.

Measure the length and diameter of each of your steam mains and tell us what vents are on them. This would be a great time to balance the main venting, which will make the system heat faster and more evenly, saving fuel.

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