main vents

butlermog

again, sorry for elementary questions. i have ordered the 'we've got steam heat' book, but am still waiting for it to be delivered.



this morning was the first time that i noticed a little bit of water escaping from my main vent in my 2-pipe system. usually i do not hear air leaving the vents until the boiler has been running for 30+ minutes, which was the case this morning. however, today the boiler was running for 45+ minutes (turned the thermostat up). so at around 30 minutes i heard air escaping the vents, and then at 40+ minutes i noticed a little bit of water squirting out. because of that, i turned the boiler off.



i still do not really understand the main vent functionality (hopefully i will when the book arrives), but i understand that when pressure builds up, air needs to escape from them. but how bad is it for a little bit of water to escape too?



can someone educate me a bit on these vents to ease my mind until i can really understand them when the book gets here.



thanks.

BobC

system pressure

The air has to leave the radiators and piping so steam can enter them. On a lot of systems the steam mains total volume are very large and they have to be emptied of air before steam will be available to feed the radiator pipes that feed from the steam mains.You want to vent those mains fast.



Do you know what pressure the boiler is running at just before the boiler shuts down? There is a pressuretrol on the boiler and it's purpose is to set the limit for pressure. Systems work best, and cheapest, when the maximum pressure is 1-1/2 to 2 PSI - any higher and your wasting fuel.



Bob

butlermog

pressure

bob, the highest pressure that i have ever seen is between 1-2psi, and the pressuretrol is set as low as it can be (i think).



do i want the system to keep between 0.5 and 1.5 psi? It takes my boiler about 30-40 minutes before it reaches that amount of pressure.

BobC

0-30's are not very good at low pressure

Actually if it takes that long it may indicate the boiler is sized correctly to the radiator load, assuming everything else is ok. The 0-30 PSI gauge on most boilers isn't very useful at low pressure. A lot of people have added an auxiliary 0-3PSI gauge so they can see exactly whats going on.



The one thing to watch out for is that your pigtail doesn't become clogged. The pigtail isolates the pressuretrol from the live steam and if that pigtail gets clogged the pressuretrol can't see the boiler pressure. i would worry about that if things start to hiss a lot loader and the boiler runs for very long periods of time. If your 0-30 read 0 when cold and increases to 1-2PSI under steam your probably fine.



All of this will become clear after you've read the book, in fact once you understand that you might want to read "The Lost Art of Steam Heat" for a thorough understanding on the subject.



good luck,



Bob

butlermog

how long is long?

bob, thanks again for your help.



you said that you would be worried if the boiler runs for a long time. but what is a long time? i've been trying to figure this out too...



when my thermostat reaches 1-degree less than the desired temperature, the boiler clicks on. the boiler will stay burning until the thermostat reads 1 degree more than the desire temperature. so, to get the temperature to rise those 2 needed degrees almost always takes 30-35 minutes. is that what you would call too long? we keep the house quite cool (because we are trying to use less fuel), but is it possible that we are doing more harm by keeping the house colder, and therefore allowing the radiators and pipes to cool down to 'room temperature'?



is a 30 minute running time what i should expect always?

BobC

Too long

What model boiler do you have and what is the nameplate rating in sq ft of steam? Next how many radiators do you have and what size is each one? Add them all up and see how close your load is to the boilers rating.



Use this to calculate what you have - http://www.usboiler.burnham.com/contractors/tool-box-sizing   - and ask if you have any questions.



If the system is very well balanced it takes a long time to build pressure, as long as the house heats ok and there aren't any unresolved issues you could be fine.



My system is much smaller that yours and way overfired (boiler has more capacity than the load warrants) , it takes 15-18 minutes to reach the 12 oz cutout limit from a cold start.



Bob