Main Vent Location

arches · December 2009

I'm looking for some advice on selecting a main vent location for the main in the picture below. Our building has over 200' of steam main in the basement (primarily 2.5") with only a single small radiator vent (not a main sized vent!) in the longest main. That vent has (not surprisingly) failed and will be replaced with a Gorton #2 or several #1s.

I'd lalso ike to tap in three new vent locations so each main is well vented (the boiler is centrally located and the mains radiate out to the four corners of the building in various configurations).

From reading Dan's book and this site, I know that the recommended location is downstream of the last riser takeoff and at least 15" from the end of the main. However, in this circumstance, the last takeoff is located just two inches or so from the end of the main. Is it better to move upstream? Install downstream on a longer vertical nipple (I have abt 18-20" of headroom above the main)? Install in the upper part of the dry return? I plan on using the antler or menorah style installation.

Any help you can provide would be much appreciated! And yes, the mains will be insulated once the vents are installed.

nicholas bonham-carter · December 2009

best location for vents

is this a counter-flow system with no dry returns? if so, you are stuck with the necessity of finding a convenient location at the end of the main. with 200 total feet, in perhaps..4 arms, i would put 2 gorton 2's on each, as i feel there is safety in numbers. remember that it is not only the main pipes you are venting, but also the steam chest of the boiler itself!! --nbc

jpf321 · December 2009

looks like mine...

your end-of-main looks alot like mine .. i tapped directly between what would be your T and the final descending Elbow .. I knew it wasn't a perfect location based on the recommendations here, but it was my best option I think.

I also used the "if i'm going to break a pipe or screw something up .. I should break a small pipe" mentality.

It would be nice if someone here rehashes the reasoning behind "15in min from main end and 6" min vertical above the main".

arches · December 2009

parallel flow

The mains are sloped away from the boiler, so i've been operating under the assumption that this is a parallel flow system.

The elbow at far right in the picture leads a vertical return that heads down to the floor before winding its way back to the boiler. I'm assuming the upper part of that is considered a dry return (it's above the boiler water line when the boiler is at rest)....but I'm new to the terminology!

arches · December 2009

tapping tips?

Yeah, that little section is definitely an option...I just imagine there will be a lot of condensate splashing around there as it flows back from the riser.

I saw in your post on installing the vents that you discovered some "tricks" to the tapping process as you went along...anything worth sharing? I already have an angle drill, a nice sharp tap and the 45/64 drill bit.

jpf321 · December 2009

tips...umm...

i was stuck between a floor joist and a hardplace .. the first day I tapped, I didn't have an angle drill, so it was a bear. the second day I had a close-quarter drill, but it wasn't truly much better .. what did help was a 90deg adapter (about $20 at a big box home supply store) on the close-quarter drill..additionally, i dipped all my bit and tap in thread cutting oil as I went. another tip...just use a single pilot hole (1/8th)...don't try to work up from say 1/8th to 1/4 to progressively larger .. this will cause many more problems. i'm a numbnut and I didn't realize that 45/64 was a bit size (since all references here just say 45/64 drill not "drill bit") and thought it was a drill type .. i used instead a 3/4" Mason Bit. Mainly because I thought I needed a 3/4" bit for the tap and the drills I were using only had a 3/8" chuck. the mason bit worked just fine...and the 3/4" size worked ok as well it's only .05" larger than 45/64. i used some extra telfon tape and joint compound. once I punched the hole basically through and the drill started to bind, i used my dremel to clean it up. i also didn't have a tap-handle large enough for that size tap so I used a 6inch adjustable crescent as my handle. everything worked out well in the end .. but it was definitely a HO job rather than a PRO job.

I hope some people got a chuckle out of my above job execution.

Big-Al_2 · December 2009

Varivalves

This is what I would be tempted to do: I'd put the vents just upstream of the last riser. The last radiator vent would have to vent the last few inches of main, but that shouldn't slow things down enough to matter.

I'd also be tempted to use Heat Timer Varivalves as mini-main vents . . . the ones with the inlet on the bottom, not the side. They vent almost as fast as a Gorton #2. You'd only need to tap 1/8" NPT holes in the main, which would be much easier than tapping in a 1/2" or 3/4" pipe for a typical main vent. You could put three or four of the Varivalves on the main, each on their own tapped hole, each on a 6" tall, 1/8" riser pipe.

Or . . . If it's a single-pipe system, you could just try putting right angle Varivalve vents on the last couple of radiators, and venting through them. It would be simple to try . . . but you might get some spitting, especially with a non-insulated main and riser. Insulation would certainly be in order too . . .

Main Vent Location

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