Where do the main vents go when you have a dry return?

Big Ed

It needs to be located right after the last used riser. I being a guy that will be the one to service it ,would put it in the boiler room . Away from the last ell that drops down to the boiler......

Angela_2

Hi Heating Gurus,

I am having main vents installed on two one-pipe steam systems with dry returns. Since the Lost Art talks mostly about wet returns, I am not exactly sure where these vents should be located.

In the first system, the main leaves the boiler, runs around the basement and returns to the boiler. the Main is higher on one side than the other-- I assume that the higher side is where the steam would go first? The heating guy who was here last week said that the main turns into the dry return about halfway around, but I'm not sure that makes sense, since there are still risers coming off it after that point. I am confused about what part of the system is the dry return and which part isn't, and that leads to a great deal of confusion about where to locate the main vent or vents according to Dan's instructions. The very last pipe coming off the main before it goes back into the boiler looks like it might be a condensate return, since it can't be a radiator (there is no radiator in the middle of my foyer floor, and I've identified the other risers to radiators). Would I place the main vent between the last riser to a radiator and this likely condensate return?

In the second system, two mains run in two directions, then turn around sharply and come back to the boiler, so it's clear where the dry returns start. The instructions say that the main vent should be 15 inches back from the end of the main, but there is a picture in the book that shows the vent at the end of a dry return instead, back in the boiler room. If these vents should in fact be in the boiler room at the end of the dry returns, what is the correct placement-- also 15 inches back from the end? There are already two mains there (I think clogged or otherwise ruined). They are at the very end of the returns in the type of tees that Dan says should be avoided.

I'd appreciate any good advice before I have these pipes drilled.