Vent Stack or Vac System Exhaust???

[watercamper]

First post. Here goes. The roofers need to change the location of a pipe penetration through my roof. I THINK I can simply cut it off in the attic as I THINK it is just for a central vac exhaust. My question: Is this a plumbing vent stack or a central vac vent?

The pipe is EXACTLY 2" OD. It is not the 1 7/8" OD or 2 3/8" OD PVC that I can find at all of the stores in town. My house is piped for a central vac system. It was built in 1982.

I've attached 3 photos:
#1 shows the pipe coming horizontally out of the wall then turning vertical (I am in the attic). You can't see it in the photo but the horizontal part of the pipe turns vertically downward through a wall. On one side of the wall is a toilet. On the other side is the garage. However, right at this location in the wall in the garage is a 2" ID elbow for attaching a 2" OD pipe for attaching a central vac.

#2 shows the pipe going up through the roof.

#3 shows the exterior which looks nothing like my other roof penetrations which I believe to be plumbing vent stacks.

I attached my shop vac to the elbow in the garage and put it on discharge. I couldn't really feel any air coming out of the pipe up on the roof. I had to tape up the central vac ports in the house as air was coming out of them. This little test has me wondering if my thoughts are correct that this is part of the central vac system or is in fact, part of the plumbing system and should be plumbed correctly outside the attic. All help will be appreciated!

 

[johnjh2o]

It look like it it is for the central vac to confirm that turn on the vac and there should be air blowing out of the pipe. I have never seen them vented through the roof. In most cases there just vented through a side wall. I can also see why the roofers what to move it. It's in the valley.

 

[watercamper]

A central vac system was never installed. That's why I tried my shop vac on blow but couldn't get any feel of air up on the roof. Most of the air from the vac seemed to go inside the house.

And yes, the valley is why the roofers want to move it. They installed the flashing as shown but the angle and the valley and winter ice and rain caused a leak. Now they want to do it right.

Any other thoughts??

 

[phishfood]

Also, the true 2" OD sounds like a vac system. I have had to cut off unused lines on a vacuum system, and found that regular PVC caps would not fit, so I had to use a rubber cap with a clamp.