Fast Main Vent, Slow Rad Vents - How Come?

Chris M_2

All,

Why is it that having as big a main vent as possible, while keeping the radiator vents more restricted is the optimal setup?  In other words, wouldn't it be better to get the steam filling the radiators as quickly as possible, so as to keep the burner's firing time at a minimum?  -I have a Burnham Megasteam 396, Beckett AFG burner.   -Thanks

BobC

Venting

The mains wantb to vent fast so you can get steam to all the radiator pipes at about the same time. If you vent all the radiators very fast there will be two problems.



The radiator pipes are small compared to the steam mains so if you fill them with steam very quickly, the condensing steam that is flowing back to the boiler may well interfere with stem coming up the same pipe on a single pipe system.



Very fast venting often leads to balance problems because the steam will go to the easiest path and not to all the paths if the venting on the radiators is too fast.



Remember ALL these systems were designed for coal fired boilers that produced steam a lot slower than modern boilers do. They were outfitted with VERY slow radiator vents and much slower main vents than we use now.



Bob