Are thermostatic vents necessary on two pipe system dry returns?

tlowc34

Open pipe would work, right? Steam shouldn’t be in the dry return unless boiler pressure is too high and you’re flash steaming in the return. No?

With coal I can understand. But with natural gas and building insulation creating really short cycle times the thermostatic function seems unnecessary. I would almost think you want an indicator of steam escaping the dry return to know you have a bad trap. But I’m a noob, so I’d love to discuss.

JUGHNE

On larger systems with +1 million btuh boilers, I have put tees with open riser pipe as high as possible. Those had multiple dry returns to a cond pump. If steam showed up coming out of any of these risers, the area of steam trap failure could be narrowed down. All the risers were in the boiler room so as to protect finished areas.

On a smaller residential system that was gravity return, I did install G2 vents. The HO may not notice any steam passing if it happened.
So if you visit your boiler room often you may see if you are passing steam.
A goose neck fitting set up with 2 90's would have any cond dripping go back down to the return pipe rather than spitting up to the ceiling.

Jamie Hall

Not only would open pipe work -- it frequently did in some older systems. Still, it's not a bad idea to have a vent -- like @JUGHNE , a G2 is a very good choice -- and on some vapour systems (Hoffman, for instance) a vent is actually required -- but isn't there for the reasons you might think.

tlowc34

Mine is a Trane system with the milk jug sized return trap still in place (but possibly leaky, sight glass is dry). Similar to Hoffman?

Jamie Hall

Vaguely... take a look in The Lost Art. They're both in there -- both vapour systems.