return vent sizing

4Barrel

hi all -



two issues:



i'm assiting a friend with turning up a one-pipe system (small sucker for about a 1800 sf home, about 22 feet of 2" main, and baout 15' of 1.5" main). 2 vents are located at the ends of the dry returns (poor little buggers.. pics attached). the run outs do not have returns, only on the mains themselves. that's it. 



so i;'m planning on replacing the return vents pictured with Gorton #1's, but would ask:

- is that enough?

- should i isolate the vents from the elbows to the loop (as is suggested in this thread:

<a href="http://www.heatinghelp.com/forum-thread/140167/dry-return-vents">http://www.heatinghelp.com/forum-thread/140167/dry-return-vents</a>)?



next issue:



this matter got me thinking about my own system, where i do not have the dry returns with their own vents. I installed locations for them, so they are easily added, but I chose to vent the mains near the end of the runs. so, as a more general question, is venting on dry return where you otherwise have venting on the mains a good idea? my system runs well, but if opening up the dry returns to venting gets me condensate returning that much faster, i think i'd like to try it.

BobC

maybe 2 vents on the 2"

20 ft of 2" pipe has 0.46 cf of air and a Gorton #1 is rated at 0.33cfm so you might need 2 on that one but try it with 1 and see how it works. The 15ft 1.5 main has 0.21cf of air so one Gorton #1 sb fine. You may find you need the extra Gorton #1 vent on the 2" main to balance things out but try it and see how it works.



I have a setup like yours and installed an elbow and a length of pipe to get the vent away from that T, just make sure that pipe has some slope so condensate can find it's way back to the boiler.



Bob

nicholas bonham-carter

How much venting?

The only way to be sure of the correct amount of main venting you need is by measuring the back-pressure with a good low-pressure gauge. 0-3 psi from gaugestore .com.

As the steam fills the pipes, it must have very little resistance to pushing the air out of the mains so that they are completely full of steam before the risers begin to fill with steam. The radiator vents should be the slow but sure Hoffman 40's. Their increased resistance to airflow will make sure that the steam arrives at all radiators at the same time on one floor. If you have a tall building, then you can increase the radiator venting at the top floor only.

So after you have figured out the volumes of the pipes, and the steam chest, etc, check your main venting performance with the gauge. If you have more than 2 ounces during the venting phase, put another vent on the menorah. If your main vents have any significant back-pressure, then the steam will begin to rise up into the radiators unequally, and you will be tempted to play around with larger and smaller radiator vents untill you are sick of it, and have a growing pile of discarded vents in front of you. Remember that you can never have too much main venting, so if you think you may need one, then put 2 on each main. The lower velocity of air escaping will also keep the vents from plugging up. If you are considering the expense of the vents, then consider the cost of paying the fuel company to force the air out of the system through some constipated little openings of inadequate vents.--NBC

4Barrel

return vents?

Thanks NBC. Any thoughts on the positioning of vents on the returns on a system that already has the mains vented?

nicholas bonham-carter

Main vent placement

I think the present dry return location is the best place to put the vents, because it enables the home owner to keep an eye on them more easily in the boiler room instead of being elsewhere in the building. He can occasionally feel the pipes to see if one is heating up more slowly due to a plugged vent. The low velocity of escaping air will also decrease the chances of a plugged vent as debris is less likely to be trapped by a small opening.--NBC

PMJ

JUST VENT DRY RETURN ON 2 PIPE

On my 2 pipe system I have used your method of checking the pressure with a gage - but in the dry return. IMHO there is enough venting when there is zero pressure in the return AND you never hear any air coming out - ever. If you do hear anything the hole you are opening to let out the air as steam comes into the main is too small. Plainly there is no such thing as a hole too big in the dry return when you are trying to get steam to the rads. Any pressure in the dry return just slows the steam trying to fill the rads - any. 

On a two pipe system at burner on all the rad traps are open so the steam main, rads, and return lines are all effectively one open pipe. I have no vent on the steam main at all because there is no resistance to the steam going to the rads - they are wide open through their traps to the dry return which is wide open to the atmosphere. Some of the biggest rads (whose traps never close because they never fill all the way across unless it is 30 below) happen to be at the farthest end of the loop from the boiler so the main is always effectively vented at its end through those rads. There literally is never a time when the steam main is not vented through at least a couple of rads with still open traps even when most have closed.

With this method the last rad to get steam(out of 21 on two floors) gets it within a minute of the first one to get it on first startup from cold and significanlty better than that cycling from vacuum when the whole system is already hot.

4Barrel

new main vents installed

hello -

a follow up on my first issue... i replaced the main vents as advised on my buddy's small system, worked like a charm! pics attached. however, someone had turned the pressuretrol all the way up, damaging the radiator vents, all but one is functioning, so i've ordered hoffman 40's to replace them as NBC suggested. thanks!



i'll post separately on my main vent issue...

4Barrel

my main vent location

so fixing my friend's main vents i had gotten me to thinking about the physical location of the main vents on my one-pipe steam system. it's a 225K dunkirk, covering four apartments and about 3000 sf of livable space. it's always been a challenge balancing the system. it's not bad, but i'm always fussing with it. i laughed when NBC said i'd end up with a pile of radiator vents - yep - i've been there. i wondered if it made a difference if i added vents to the returns in addition to the ones located at the ends of the mains themselves. so i temporarily re-purposed the low pressure gauge (0-20 oz) i have paired with my vapor-stat and measured the back pressure at both dry return locations (pic attached). much to my surprise, the needle hardly moved during the venting phase (which for me is more like 8-10 minutes from a cold start). maybe a 1/2 an ounce. that's it.



so what does this mean? is the system sufficiently vented? would adding additional vents to the dry returns be overkill?



and, does it even matter where they are located? i see a lot of sense in installing them at the dry return location, for reasons stated in this thread... i went through a lot of work to install the main vents at the ends of the mains. but could i have accomplished the same thing by installing them on the dry returns near the boiler instead?

nicholas bonham-carter

main vent location

the main vents are better on the ends of the dry returns, next to the boiler. you can feel the difference in relative temperature more easily. if the dry returns are not vented, then the system should work, but you never know when you have enough venting on each leg

it is easier to feel for steam arrival in the dry return, instead of condensate arrival..--nbc

4Barrel

move them?

thanks nbc...

so what's your take on this? is it worth relocating all the vents to the dry returns?

or maybe just add a couple #1s there and see how it goes?