Venting the Main's Q

Reinvent

I usually see vents for the main pipes at the end of the drip return or at the end of the run near the boiler. Why not instal the vents on the main just after the last branch? Filling the returns is not helping the rads as far as I can see.
Also if I wanted to ad venting in existing mains by taping a hole, how do I do so with out getting metal debris in the pipe?

EBEBRATT-Ed

You need to vent the air out of the dry returns so the condensate can slide back to the boiler easily. Air will not go down the riser into the boiler and trapped air will slow down the condensate return.

Depending on the holes size your drilling you might drill a little and put a magnet on the drill bit drill, stop, drill stop. You can probably collect some of it and the rest will be just minor debris. won't hurt anything. Same with the tap.

Jamie Hall

And furthermore -- if this is a two pipe system, the air leaving the radiators to the steam can get in goes into the dry returns. if the air can't leave the dry returns, it can't get out of the radiators and the steam can't get in.

You must vent the dry returns. It helps to vent the mains. There is a difference between "must" and "helps"...

Steamhead

Reinvent said:

I usually see vents for the main pipes at the end of the drip return or at the end of the run near the boiler. Why not instal the vents on the main just after the last branch? Filling the returns is not helping the rads as far as I can see.
Also if I wanted to ad venting in existing mains by taping a hole, how do I do so with out getting metal debris in the pipe?

The short answer is "it depends".

If this is a one-pipe system, there is no operational reason to vent the dry returns unless they are used as heating surface. You only have to vent as far as the last steam takeoff. If the mains end in a crawl space, putting the vents on the dry returns will make them accessible. The same would apply to a two-pipe, air-vent system that was originally installed with air vents on the radiators.

But as Jamie said, if the system does not use air vents on the radiators, you MUST vent the dry returns. Once in a while we see a Vapor system where Beavis and Butt-head removed something like a Vent Trap or a Differential Loop and did not install something else to vent the dry returns, the system doesn't heat well if at all, and the Pressuretrol is cranked up to 10 PSI or so to try to compensate. The cure is to install vents, proving that Mr. N. Hawkins knew his stuff: "And thus a little device........... will start what a ton of pressure would not do in its absence".