Apparently steam can go where there is air!

ChrisJ

So I've heard a few mention that steam can compress air in a radiator and still heat the radiator even if the vent is shut or plugged.



I think this is exactly what I'm experiencing in our bedroom.  Since I installed a G6 on the riser to this radiator combined with a G4 on the TRV I've had near perfect temperatures.  65-67F in our bedroom while the rest of the house maintains around 71F.  Well last night with a low of -3.5F my system was finally seeing some pressure.  Sizzling / hissing vents and according to my 3psi gauge around 2oz or so, not loud but certainly noticeable where normally all vents are silent.  All night that radiator kept heating some and the bedroom was staying between 68-69F.  Thinking maybe the vacuum breaker as clogged or something weird was going on I removed the TRV and did the ol mouth test.  Vacuum breaker was clear and I am 100% sure the TRV was shut not allowing any venting.



Seems like its just the way its going to be if I want that riser vented and if I remove the vent the room will stay too chilly with a G4 on the TRV or overheat really bad (75+F) with a G5.  Before the TRV I was seeing temps approaching 80F on very cold nights even with a Hoffman 1A venting as slow as I could get it so this is certainly a huge improvement.  The radiator isn't even really needed in that room especially on cold nights.  I think the only time I ever want heat from it is if its windy out, then it will start heating and things are nice with the TRV. 



Just wanted to share my experiences with others.  An unvented radiator apparently can still heat some depending on the situation.  If this is what it can do with only a few ounces I can only imagine what a few pounds will do.

Jamie Hall

Yup -- there are no absolutes!

and you are basically quite correct -- if the pressure rises a little, some air will compress and allow some steam in -- not much, maybe, but if it gets to 2 psi, for instance, about an eighth of the radiator will have steam in it.  Which, of course, will condense and heat the radiator.  And so on...

ChrisJ

Idea

So now that temperatures have been above 0F the bedroom is back to normal.  Even with a low of 5F last night it did just fine.  So after thinking about it I finally came up with a solution to keep temps down even when its below 0F out once every 5-10 years.  Install a 1/8" ball valve on the riser vent to shut it off under those extreme conditions.  Certainly easier than trying to repair the original valve on the pipe.



Keep in mind its not that I'm this picky, I also enjoy tinkering with this stuff and enjoy striving for perfection.

Now I just need to find a decent 1/8" valve rated for steam.  This one looks about perfect.

http://www.pneumaticplus.com/mini-brass-ball-valve-male-to-female/