Is two automatic air vents necessary?

shredmaster

I have a Weil Mclain CGA 5 boiler, the illustration manual has two air vent 10 and 13 but i've seen some very experienced plumber only install automatic air vent on position 10 like this video. https://youtube.com/watch?v=f3JXaU3XGGg


I like to keep things simple and not install additional air vent but would like to know disadvantage not having one.

Ironman

#13 is actually an MBR and is more critical than #10. If you have a bladder expansion tank (as pictured), you must have #13 to vent the system.

shredmaster

thanks for quick response. the manual sounds like #13 can be optional.



how is #13 different from #10, aren't they both just eliminating the air?

Ironman

It depends on the type of expansion tank. If you have the old style compression tank, then an air separator (MBR) should never be used. Instead, a means to move air from the top of the boiler to the tank should be employed to maintain the air cushion in the tank.

If you have a bladder tank, then an MBR must be used to remove air from the system.

The alternative method shown in the diagram may work, but it's not as effective as using a Micro Buble Resorber. I would use it on a system with cast iron rad's where any air not removed at the boiler would automatically go to the top of he rad's and be manually bled.