Magnehelic gauge installation

[Michael Zerance]

In my current shop, I have two magnehelic gauges; one for the dust collector and one for the paint booth. The dust collector magnehelic is recessed into the wall and I ran two tubes; one to the dust collector and one that just hangs down a few inches from where it exits the drywall on the inside of the closet. The spray booth magnehelic is surface mounted on the side of the exhaust plenum with one port open to atmosphere and one barb fitting poked through the sheet metal to the interior of the plenum. Both of these work as intended.

I'm now in the process of building a new shop and we're almost done with the rough in prior to drywall. I want to remote mount both magnehelic gauges like my current dust collector gauge. I already ran a single tube from the gauge location to the dust collector and spray booth. My question is, if the gauge is recessed in the wall, can I just leave one of low side ports open inside the wall or do I need to run another tube for each gauge that is open to atmosphere somewhere in the room?

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[Ron Selzer]

As long as the wall cavity is not sealed then you will be fine. If the drywall is glued all the way around, all electrical boxes sealed, etc. Then yes you would need to a common tube out to the interior.
Ron

[Michael Zerance]

Thanks for the info Ron.

[Alan Lightstone]

First of all, nice seeing someone else from Tampa Bay on the forum, Michael.

Why would you want a Magnahelic gauge in the paint booth? I get having one on the dust collector (I have one there too), but really interested in its use in a paint booth. To tell you when it's time to change the filters?

[George Yetka]

Im not sure of cost but a "ball in the wall" is a quick indicator of room pressure

[Mike Cutler]

Run the tube to the location it needs to sense.
You're dealing with "Mouse Farts" with a 5" Magnehelic.
Properly installed, that gauge can sense a door opening and closing, and the ambient temp change effect on pressure in a room, due to opening and closing a door.
I've been installing, repairing, and calibrating, these gauges for close to 40 years in industrial environments. They're nice.

[Michael Zerance]

First of all, nice seeing someone else from Tampa Bay on the forum, Michael.

Why would you want a Magnahelic gauge in the paint booth? I get having one on the dust collector (I have one there too), but really interested in its use in a paint booth. To tell you when it's time to change the filters?

Hi Alan. Yes, it's to measure the load on the filters. I think most spray booths use a simple liquid filled manometer but I had an extra 0-3" magnehelic so used that instead. It works well.

Run the tube to the location it needs to sense.
You're dealing with "Mouse Farts" with a 5" Magnehelic.
Properly installed, that gauge can sense a door opening and closing, and the ambient temp change effect on pressure in a room, due to opening and closing a door.
I've been installing, repairing, and calibrating, these gauges for close to 40 years in industrial environments. They're nice.

Thanks, Mike. So, you're saying it's okay to just run one tube to the source and leave the low port open inside the wall?

[Bill Dufour]

Jut poke a 1/4" hole somewhere into the stud cavity with a pencil.
In a bath remodel. I disconnected the vent stack and used a sanitary vent valve inside a wall cavity. Only vents the vanity sink. Drain works fine for about one minute then it slows down a bit as the air is sucked out of the stud bay. I could drill a vent hole or two up from the crawl space but not worth the trouble.
Bill D.