How do I calculate main vent sizing?

Jane_7

Hi-- I would like to make sure my main vents are properly sized. I have 2 main vents, located at the end of the 2 dry returns before they drop to the floor. They are both Vent-Rite #75, which my plumber recently installed. I am not sure they the right size however, and would like to confirm.



I have attached a diagram of my basement piping.



Here are the sizes and lengths of all the basement pipes for the main/return #1 and #2:



Dry returns:

(#1) 1.25" pipes: 22.3 ft

(#2) 1.25" pipes: 21.3 ft



Steam mains:

(#1) 2.5" pipes: 22.3 ft

       2" pipes: 10.4 ft 



(#2) 2.5" pipes: 21.3 ft  

       1.25" pipes: 14.6 ft



When making my main vent calculations, do I measure both the length of the steam supply mains, AND the dry returns? I'd like to go with the Gortons. Would Gorton #2s for both main vents work? Any help would be very much appreciated.

BobC

Main vents

You need to figure out the volume of air in the steam mains, you do not have to include the return pipes in that calculation.



It looks like you have about 1,600 cu inches in Main #1 and that works out to 0.925cu ft; main #2 has 1750 cu inches which is about 1 cu ft. The Gorton #2 is rated for 1.1 CFM so it should work for both mains. BTW the Gorton #2 vents at almost twice the rate of a Ventrite 75.



Bob

Jane_7

vent sizing

Thanks so much BobC! That's a huge help. I'll order some Gorton #2s, and will post any changes I notice back on the wall. Will I be able to directly swap the Ventrite #75s with the Gorton #2s? (Are they the same threading size, etc?)

BobC

It depends

The Ventrite 75 can thread onto a 1/2" male thread or a 3/4" male thread because it has threads inside and outside. A Gorton #2 has a 1/2" male thread so will need either a 1/2" coupler or more likely a 1/2 to 3/4 reducer.



The Gorton #2 is a physically large vent, make sure you have room for it. You will need 7 to 8" on top of whatever kind of an adaptor you need.



Bob

Jane_7

Gorton thread size

Thanks Bob. I've attached a photo of the Ventrite. Can you tell from this if I need to add some sort of coupler or reducer, and if so, which one?



On main #1, I have plenty of room to work with above. On main #2, there is exactly 7" from the top of that connector piece connecting the pipe to the Ventrite. Do you think that's enough room to work with?

BobC

It will be tight

You will need a couple of 3/4 by 1/2" hex bushings like this -



http://www.grainger.com/product/29VD20?gclid=CNGK7O7yxLwCFeJj7Aoda14Agw&cm_mmc=PPC:GooglePLA-_-Plumbing-_-Pipe%20Fittings%20and%20Couplings-_-29VD20&ci_src=17588969&ci_sku=29VD20&ef_id=UvqF6gAAABFKRi2j:20140211201954:s



7' of overhead will be very tight because I believe the vent is 7" overall and you still have to get the adapter in there - but the valve screws into the adapter so it might work.  Try going to a plumbing supply store (print out the picture of the fitting and take it with you) and ask them for the bushing and valve so you can see if it will fit. If it doesn't maybe you can replace that 3/4" nipple with a shorter one.



Also the Gorton #2 is about the size of a 12oz tuna can so you need some room to swing it.



http://www.pexsupply.com/Gorton-G2-Gorton-No-2-Straight-Air-Eliminator-3524000-p



Bob

Jane_7

Coupler

Many thanks, Bob. My local plumbing supply didn't have that in stock, but I found this one at Pex Supply-- the only difference I can see is that its made of iron. Does this look right?



http://www.pexsupply.com/Ward-FBHE3-4x1-2-3-4-x-1-2-Black-Hexagon-Bushing-746000-p



Once I have the coupler and the Gorton, I assume I just need to wrap teflon tape 2-3 times around the male threadings and screw them in tightly with a wrench?

JeffM

reducing coupling

If you don't have quite enough height for the vent and the additional bushing, you could remove the coupling that the current vent threads into and replace it with a 3/4" x 1/2" reducing coupling. That might reduce the overall height by 1/2" or so.

http://www.pexsupply.com/Jinan-J-BLRC-0705-3-4-x-1-2-Black-Reducing-Coupling

BobC

Jeff is right

That kind of coupler should save some height, you would just need to use a couple of wrenches to remove the existing coupler and that should not be hard because the pipe dope looks fresh.



A few wraps of teflon tape would be fine but try not to get tape on the first couple pf threads so it doesn't strip off and get into the vent.



Bob

Jane_7

Couplers

Many thanks Jeff and Bob. I will order a couple of both of the couplers/reducers you recommended, and hope that one will work!

Jane_7

Pipe size correction

Hi again,



I just realized I think I wrote the pipe sizes incorrectly in my original post, as those were what appeared to be the outside diameters. The actual pipe diameter, I believe, is as follows (these new dimensions are based on the size of the insulation I used on these pipes, which fit snugly). Sorry for the confusion--all of this is very new to me, which must be pretty clear...! Are 2 Gorton #2s still appropriate for my system?



Steam mains:



(#1) 2" pipes: 22.3 ft



       1.5" pipes: 10.4 ft 







(#2) 2" pipes: 21.3 ft  



       1" pipes: 14.6 ft



Thanks!

BobC

That changes things

BUT not enough to select a different vent. You could get by with 2ea Gorton #1's on each main but then you would need elbows, T's, and nipples so the cost would be very close. Nobody ever has to much main venting so you should probably just stay the course and use the Gorton #1's.



BTW what kind of radiator vents are you using.



Bob

Jane_7

Radiator vents

Thanks--Ok, I'll stick with trying the Gorton 2s on the mains.



On my radiators I currently have a mix of new Home Depot air vents and vent-rites. However, I just ordered a Gorton #4 for the room with the thermostat and #5s for all the other 7 rooms. None of the radiators are very large, except for 1 in a small room. Does that sound like a good approach?