Vent Systems 6” Inch Galvanized Steel Tee Cap - Heavy-Duty HVAC End Plug for Dryer Ducts, Exhaust Pipes, and Round Metal Vents – Indoor and Outdoor Use – Closure Fitting for HVAC Systems

A simple, well-made way to finish a 6-inch duct run

Sealing off idle ductwork is one of those small jobs that pays dividends in comfort and efficiency. I’ve used plenty of improvised fixes over the years—sheet-metal circles, crimped scrap, even a plastic plug in a pinch—and they always look temporary or leak more than I’d like. The Vent Systems 6-inch tee cap is the tidy, purpose-built end I reach for now.

What it is and where it fits

This cap is designed to push into standard 6-inch round HVAC ducting, whether that’s rigid snap-lock pipe, a wye/tee takeoff, or the end of a semi-rigid dryer line. It’s a male-style closure: the spigot inserts into the female duct, then the face of the cap sits flush against the pipe edge. On my bench, the spigot slipped into several brands of 6-inch pipe with consistent friction; in the field, it fit both a sheet-metal tee branch and the interior end of a dryer vent with minimal persuasion.

The cap I received included a thin rubber gasket around the spigot. That gasket is the difference between “good enough” and “done right” if you care about leakage and pressure balance.

Build quality and materials

The body is galvanized steel—stout enough that it doesn’t oil-can when you press it in, but not so thick that it fights you. The galvanization is even, with no bare spots or rough crystallization. I didn’t see metal flakes or poorly formed seams, which is more than I can say for a lot of budget HVAC fittings.

Edges are reasonably clean, but they’re still sheet metal. Wear gloves; it’s easy to catch a knuckle when you’re working inside a ceiling or behind a washer. The gasket appears to be EPDM or similar and sits in a formed channel so it’s not just glued on. After a couple of insertions/removals it stayed put and didn’t deform.

If you’re capping outdoors, the galvanization gives it a fighting chance against weather. I placed one on an exterior stub-out for a month through rain and a few hot days—no rust bloom or discoloration. If your site is coastal or sees road salt, I’d still tape the seam and put a dab of clear sealant on the top edge to keep water from sitting behind the lip.

Installation: tool-free, but I still tape it

The install process is as simple as push, align, secure. A few tips from my uses:

• Measure the duct’s nominal size and confirm you’re working with a true 6-inch round. Older ducts can ovalize; a quick squeeze with hand seamers will bring them back to round if needed.
• Deburr the duct edge if it’s jagged. A clean edge protects the gasket and helps the cap seat fully.
• Seat the cap by hand with even pressure. Twisting 10–15 degrees as you push helps the gasket slide instead of roll.
• I always run a ring of aluminum HVAC foil tape around the seam, even with the gasket. It’s cheap insurance and adds mechanical security. Avoid cloth “duct tape”—it fails quickly and leaves a mess.
• For vertical runs or areas where someone might bump the cap, a single sheet-metal screw or a clamp band makes it bulletproof. Pre-drill so you don’t tear the gasket.

With the gasket engaged, I didn’t need screws on interior lines. For a horizontal branch on a basement trunk, I used foil tape only. For an exterior dryer vent stub that could get jostled, I added one 1/2-inch screw through the lip into the duct and then taped over it.

Sealing performance

I check seals with a smoke pencil or an incense stick and a manometer when I’m curious. On a return-side cap over an unused 6-inch takeoff, the gasketed fit showed no visible smoke wobble at typical static pressures. On the supply side at higher pressure, a faint flutter appeared before taping; taping eliminated it. In a laundry room where I’d converted to a ventless dryer, capping the interior end of the old 6-inch vent stopped a persistent draft that you could feel with a hand in winter. That’s the practical difference the gasket makes.

Will this completely transform a leaky system? Of course not. But if you’re plugging unused runs, it keeps the air where it belongs and helps stabilize room pressures without resorting to spray foam or mastic blobs.

Where it makes the most sense

• Dryer vent decommissioning: If you’ve migrated to a ventless dryer or rerouted a vent, this makes a tidy, fire-safe interior cap. Pair it with foil tape and you’re done in minutes.
• Unused takeoffs on trunks and tees: When I adjust zoning or cap redundant branches, these give me a reversible closure—no crimping a can and hammering it flat.
• Temporary testing or balancing: Because it’s tool-free, I can block a run during airflow tests and remove it later without mangling the pipe.
• Garage, attic, and utility room stubs: Those random six-inch stubs that whistle on windy days? This quiets them.

Durability over time

I’ve had one of these in a damp basement for several months on a supply branch that we’d abandoned during a remodel. No corrosion so far, and the gasket hasn’t dried out or stuck to the pipe when removed. The face stays fairly clean; if you’re using it where it’s visible, it looks like a factory end rather than an improvised patch, which I appreciate.

Outdoors, the galvanization held up in normal rain cycles. I did observe minor water staining where the face meets the pipe on a vertical stub—nothing structural, and a thin bead of clear exterior sealant under the top half of the lip eliminated it. If you expect direct sun and heat, the cap stays cool enough; the steel doesn’t warp the way some plastic caps do.

Limitations and things to watch

• Size accuracy matters: Duct “6-inch” is nominal. If you’re trying to cap thin-wall flex that’s been chewed up near the end, cut back to a clean round or use a short rigid collar first. Out-of-round ducts will compromise the gasket.
• Not for active combustion vents: Don’t use this to close a live furnace, boiler, or water heater vent. If you’re decommissioning any combustion vent, follow local code and ensure proper termination or full removal.
• Long-term security in high-traffic spots: In garages or utility rooms where things get banged around, add a screw or a clamp band. The push fit is strong, but mechanical retention is cheap peace of mind.
• Sharp edges: Better than a lot of stamped caps, but still sheet metal. Gloves on.

Small quality-of-life tweaks

On a vertical pipe where I wanted periodic access, I added a small machine screw through the face as a pull knob. Works great and doesn’t affect the seal when it’s placed near the center. For visible locations, a quick wipe with mineral spirits removes any factory oil and helps tape adhere cleanly.

The bottom line

This is a straightforward, well-executed cap that does what it should: it fits correctly, seals reliably, and installs in seconds. The galvanized body feels appropriately stout, and the included gasket turns a basic mechanical plug into an airtight closure in most real-world scenarios. I still tape the seam in nearly every case—good practice in HVAC work—and I’ll add a screw where I expect abuse, but neither is a workaround for a flaw; they’re just the right way to finish the job.

Recommendation: I recommend the Vent Systems 6-inch tee cap for anyone needing to close off round duct runs cleanly—especially for decommissioned dryer vents, unused takeoffs on trunks, and temporary testing. It’s inexpensive, durable, and faster than fabricating a blank, with a more professional result. Measure carefully, use foil tape, and you’ll have a sealed, tidy termination that looks intentional and holds up indoors or out.