Outside air connection to return plenum

[David Meiland]

As far as I know, this is a barometric air inlet. It's connected to the return plenum of a forced air system, in an attic filled with blown-in fiberglass insulation. I believe the air handler was not running when I took the photo. In general, I expect these to be ducted to the outdoors when I see them, rather than drawing air from the attic or crawl space. More often than not they are motorized dampers wired to the air handler, instead of barometric types. This one does not appear to be designed to have ductwork attached to the upstream side, and I believe it's actually designed for use on a flue. The ductwork dates to 1990, and I have no idea what the code was then. Any thoughts?

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[Bill Kibbel]

That's a barometric draft control. It's only manufactured to be installed on a vent connector or in the chimney flue for oil-fired heating equipment.

[mjr6550]

Make up air, or outside air connections to return ducts has been standard practice (and code) for many years in commercial buildings, but not typically in dwellings. It looks like a DIY installation. It could work, but its a crude approach.

I would suggest capping it off.

[David Meiland]

As far as I can tell, code here has required makeup air for years, and what I usually see is a 6" duct from outdoors to the return plenum, with a motorized damper. I'm pretty sure those provide far more than most houses need.