opening and closing radiators for steam heating system

MikeB001

I have several rooms where I don't typically heat unless needed for some occasions. I can open radiators as needed without any concern for boiler water level when I turn them off again?

KC_Jones

The valves typically won't seal completely. The steam still gets through in small quantities. It then condenses and as water it's "bigger" and won't drain back. This can slowly fill the radiator up and rob the boiler of water.

Question, what do you hope to accomplish by keeping them off?

Closing them down effectively oversizes the boiler which can lead to short cycling which isn't as efficient. Also keeping a room "unheated" puts its load (in part) on the surrounding rooms so in a sense you are still heating that room.

MikeB001

I see your point...however I was thinking since the radiators are in my garage and another in my finished attic (un-insulated) are isolated from other rooms
BTW, i have a two pipe system...so you are suggesting condensate/water would not drain from the trap with the valve close or mostly closed?

Fred

On a two pipe system, any condensate will drain back to the boiler. There is still an issue with over sizing the boiler when you close radiators off. There a good chance your boiler is already over sized, so you'll be adding to that issue.

KC_Jones

Correct, I was foolishly assuming 1 pipe. My mistake on the drain back.

Jamie Hall

The only real problem which might crop up on a two pipe system -- other than increasing any short cycling, which may or may not be a problem depending on how big the rest of the system is -- may come up if one or more of those radiators are in spaces which go below freezing. As noted, it's rare for a valve to close completely on steam, and the small amount of condensate will drain -- unless it freezes in the trap (ask me how I know). It won't do any damage, most likely, but will prevent the radiator from heating when you do turn it on. Hair dryers fix the problem...