Red Devil 089650 Extreme Temperature HVAC/R Silicone Sealant, 280 ml, Aluminum, 1 Pack, Made in USA

Why I reached for this silicone in my HVAC work

Loose seams on galvanized duct, a whistling return plenum, and a line-set penetration that had turned into an insect highway—those were the annoyances that pushed me to try the Red Devil Extreme-Temp HVAC silicone. I wanted a sealant that would hold up to furnace cycling, outdoor UV, and the occasional splash without turning brittle or peeling off. The aluminum color was an unexpected plus: it blends in with sheet metal far better than bright white or clear silicones, so repairs don’t scream “patch job.”

After a few weeks using it on metal ducts, an exterior wall penetration, and around an appliance chase, I came away with a clear sense of where this product shines and where you’ll want something else.

Cartridge and application experience

This is a 280 ml cartridge that fits a standard caulk gun. The nozzle cuts cleanly, and bead control is good—firm enough to stay where you put it, but not so stiff that your forearms hate you by the end of a long run. Like any cartridge silicone, remember to puncture the inner foil seal after cutting the tip; otherwise, pressure will find the weakest path (usually out the back or a seam).

Red Devil recommends clean, dry surfaces and removing old caulk. In practice, that matters a lot. On duct seams, I degreased with a quick solvent wipe, knocked off oxidation with a Scotch-Brite pad, and vacuumed dust. On concrete and fiber-cement, I brushed out loose grit and made sure the surface was bone dry. With that prep, adhesion was excellent.

Tooling is straightforward. I got the best results using a small plastic caulk spreader; a gloved finger also works if you keep a rag handy. It skins over at a reasonable pace—enough open time to smooth long beads, but not so slow that dust becomes a problem. I avoid overworking it; two or three light passes give a tighter, cleaner fillet.

Cleanup is typical silicone: wipe excess immediately and use a solvent on fresh material. Once cured, you’re in the mechanical removal world (razor and patience).

Adhesion and material compatibility

The product claims good adhesion to metal, aluminum, concrete, glass, fiberglass, vinyl, and many plastics. That lined up with my experience:

• Galvanized and aluminum sheet: Excellent grip and no edge lift after repeated heat/cool cycles.
• Painted steel: Good, provided the paint was sound and lightly scuffed. If the paint is chalky, you’ll be bonding to dust—expect failure.
• PVC and rigid vinyl trim: Solid bond. I scuffed glossy surfaces for insurance.
• Fiberglass housings: No issues; adheres well around fan housings and panels.
• Concrete/masonry: Works fine when dust-free and dry. It’s not a gap-filler for crumbling edges; stabilize those first.

“Many plastics” is accurate. As with most silicones, low-surface-energy plastics like polyethylene and polypropylene can be tricky. If you suspect those, do a small test patch.

Temperature range and durability

This is where the sealant earns its keep. Rated for -60°F to 400°F, it’s clearly designed for HVAC/R environments. I used it on:

• Supply and return duct seams a few feet downstream of the furnace: no softening, blistering, or edge curl after multiple heating cycles.
• An exterior line-set penetration: exposed to sun and rain. The bead stayed supple, with no discoloration or chalking.
• Around a metal collar where a flue passes through a sheet-metal chase (non-contact with the flue itself): remained intact under radiant heat.

Silicone’s natural UV resistance is a strong advantage outdoors. After sun and temperature swings, the material stayed flexible and didn’t shrink—a common failure mode with inferior sealants. I also tested it in a cold garage install; extrusion was still manageable, and it set up normally once temperatures rose. As always, cold application demands really dry surfaces to avoid trapped moisture.

One caveat: 400°F is generous for HVAC service, but it’s not a wood-stove gasket cement. For direct, sustained contact with very high heat surfaces, use a product rated for that specific application.

Finish, color, and visibility

The aluminum color is more useful than I expected. It blends with galvanized ductwork, metal enclosures, and aluminum trim far better than white or clear. On visible mechanical rooms or exposed basement ducts, the work disappears into the background. The cured finish is a soft metallic gray—not shiny chrome, not dull putty.

Like most silicones, it isn’t paintable. Plan your bead location accordingly, or choose a paintable sealant where a matching finish is required.

Where it fits versus other options

• Versus duct mastic: Mastic is code-accepted for duct sealing and is great for larger joints, but it’s messy and slower to cure. This silicone wins on neatness, flexibility, and high-heat tolerance in tight or precise areas. For big gaps and fiberboard transitions, mastic still rules.
• Versus foil HVAC tape: Tape is fast and also code-accepted when it’s the right class. It can lift on complex shapes or dusty substrates. Silicone bridges small irregularities, resists UV, and doesn’t rely on pressure-sensitive adhesive. I often use this silicone to terminate tape edges or seal around fasteners where tape struggles.
• Versus general-purpose silicone: Many all-purpose silicones don’t hold up as well at continuous elevated temps. This one is tuned for HVAC/R service and maintains flexibility under thermal cycling.

Limitations to keep in mind

• Not paintable. If appearance matters on a painted surface, pick a different product.
• Not a structural adhesive. It seals; it doesn’t replace fasteners.
• Not for continuous immersion or permanently wet, submerged joints.
• Surface prep is non-negotiable. Oils on galvanized, dust on concrete, and chalky paint will sabotage adhesion.
• Temperature ceiling. Great for HVAC service, but don’t use it on components that routinely exceed the 400°F rating or require direct flame resistance.

Practical tips from the job

• Dry fit and mask: For visible runs, painter’s tape on either side of the joint yields crisp lines. Pull the tape right after tooling.
• Size the bead to the gap: Thin, wide fillets perform better than tall ropes. Aim for a 2:1 width-to-depth ratio on fillets when you can.
• Tool lightly: Overworking draws air and creates ridges. Two passes max.
• Ventilation: There’s a noticeable odor during application. It dissipates as the sealant cures, but good airflow makes the experience nicer.
• Puncture the inner seal: After you cut the nozzle, use a long puncture tool to pierce the foil seal inside the cartridge before pulling the trigger.
• Storage: Cap the nozzle and cover the tip with plastic wrap and a rubber band between uses. In my case, the partially used tube stayed usable for several weeks.

Value and packaging

At 280 ml, a single cartridge covered several duct seams, two penetrations, and a couple of appliance-panel gaskets with material to spare. The consistency, temperature rating, and adhesion profile justify choosing it over a generic silicone when the application involves heat or outdoor exposure. Being made in the USA is a small but welcome note for traceability and consistency.

Bottom line

I recommend the Red Devil Extreme-Temp HVAC silicone for HVAC/R sealing, appliance surrounds, exterior penetrations, and any metal-to-metal or metal-to-masonry joint that will see temperature swings and weather. It adheres reliably to the materials common in mechanical work, stays flexible from deep cold to 400°F, and the aluminum color blends in on duct and equipment surfaces. It’s easy to tool, cures to a durable rubbery seal, and resists the common failures—cracking, shrinking, peeling—that show up after a season of use.

I wouldn’t choose it where a paintable finish is mandatory, for oversized gaps better suited to mastic, or for surfaces that exceed its temperature rating. But for the core HVAC tasks it targets, it’s a dependable, tidy, and long-lasting solution that has earned a spot in my caulk gun.