Vents on steam heat mains

Scott216 · September 2022

I recently redid the near boiler piping at my house, I didn't do anything with the mains or risers. But I've been pondering over the existing venting. I've got two 2" mains. First main is L shaped and it's total length is about 30 feet. The dry return is right underneath and the same length. Back near the boiler, where the dry return drops down, there is a tee with a vent on top (vent is above the tee via 8" nipple). The second main is about 9 feet. At the end of the main the dry return drops down right away, then returns low to the ground (about 20") above the floor). There is no vent on this main.

Is the vent placement okay on the first main? At the end of the main is a tee with an unused port, so I could pretty easily put a vent here. If I did, should I remove the existing vent?

Regarding the second main, in middle of the main is tee that has an unused port that used to go to a radiator that no longer exists. I could pretty easily put a nipple here with a vent on top, but I don't know if it's bad practice to put a vent in the middle of the main. It would be possible to put a vent at the end of the main where the dry return starts, but this is very old piping and could prove to be difficult to take apart.

The vents have always been like this and I've never had problems with some radiators not getting hot.

Jamie Hall · September 2022

If it ain't broke, don't fix it. Or, as I said in another thread recently, there's ideal -- and there's works.

Now here we go again on mains and returns. Is that pipe under the longer main really a dry return? Or is it an extension of the steam main, just heading back to the boiler to carry condensate? It makes a difference. If it is a steam main extension, then that one vent at the boiler just before it turns down is as good a place as any for a vent. If, on the other hand, it is a dry return, separated by a trap (or no connection at all (except possibly a water seal loop) then the steam main probably should have either a vent or a crossover trap at the outer end (you still need the vent on the return at the boiler). However, if the heat is adequately even and there isn't more than a few minutes delay between the nearest radiator and the farthest one heating up, I wouldn't mess with it. The other short main is, when you think about it, no longer than many radiator runouts -- and again, if the radiators heat the way you want them to, without much delay, I personally wouldn't worry about trying to add a vent.

Scott216 · September 2022

Jamie Hall said:
If it ain't broke, don't fix it. Or, as I said in another thread recently, there's ideal -- and there's works.

Now here we go again on mains and returns. Is that pipe under the longer main really a dry return? Or is it an extension of the steam main, just heading back to the boiler to carry condensate? It makes a difference. If it is a steam main extension, then that one vent at the boiler just before it turns down is as good a place as any for a vent. If, on the other hand, it is a dry return, separated by a trap (or no connection at all (except possibly a water seal loop) then the steam main probably should have either a vent or a crossover trap at the outer end (you still need the vent on the return at the boiler).

Since everything seems to be working well, I agree to just leave it alone.

Regarding your question about the return, I think I'd categorize it as an extension of the steam main to carry condensate. From the boiler, the steam goes into a 2" main which is pitched away from the boiler. All the radiators are attached to it. At the end of this main, there is an elbow pointed towards the floor and it connects to a 1-1/4 pipe that is a few inched below the main and is pitched toward the boiler. It runs just under the main all the way back to the boiler, where it drops down towards the floor. There is no trap or water seal anywhere.

Vents on steam heat mains

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