Duct Insulation & Accessories Products
The groups below cover insulation, duct pipe, fittings, terminations, and the duct accessories that support and seal a system.
Duct Insulation
Each duct insulation type fits a different duct construction. Duct board is a rigid, foil-faced fiberglass panel cut and folded into rectangular trunks and plenums. Duct liner installs inside sheet metal duct to insulate and absorb fan and airflow noise. Duct wraps cover the outside of round and rectangular metal duct. Insulated panels provide rigid, pre-insulated stock for duct sections.
Duct Pipe and Flexible Duct
Metal duct pipes form round supply and return runs, joined at crimped ends and sealed at each seam. Flex duct combines an inner core, insulation blanket, and outer vapor jacket for short connections and tight routing. Duct kits group pipe and fittings for common installations.
Plenums, Collars, and Fittings
Plenums attach to the air handler or furnace openings and distribute air to the trunk lines. Start collars connect round branch ducts to a plenum or trunk. Elbows, reducers, tees, and other hvac duct fittings change direction and size. Vane and rail systems mount turning vanes in square elbows to reduce turbulence and pressure loss.
Boots, Boxes, and Terminations
Register boots and register boxes transition a round branch duct to a floor, wall, or ceiling register opening. Stack boots fit inside wall cavities to connect stack duct to wall registers. Dryer vent hoods terminate dryer exhaust at the exterior wall with a damper that blocks backdraft.
Airflow Control and Return Air
Inline dampers install within a round duct run to regulate airflow to individual branches and balance room temperatures. Mobile home return air components fit the floor and wall return paths used in manufactured housing.
Supports, Fasteners, and Installation Supplies
Air handler and furnace stands raise equipment off the floor for return air access and drain clearance. Duct support hardware, including straps and hangers, secures runs without crushing insulation. Insulation pins and fasteners hold liner and board in place, and installation supplies such as foil tape, mastic, and hvac duct sealant seal joints before insulation goes on.
How It Works and Where to Use
Attics, Crawl Spaces, and Garages
An HVAC duct in unconditioned space gains or loses heat through its wall. Wrapped, lined, or board-constructed duct slows that transfer, so supply air reaches each register closer to the temperature leaving the equipment.
Condensation Control on Cooling Ducts
In humid climates, cold supply duct surfaces can drop below the dew point of the surrounding air. Faced ductwork insulation with a sealed vapor retarder keeps moist air off the metal. Continuous, taped facing on ac duct insulation prevents dripping onto ceilings and framing.
Lined Commercial Duct
Duct liner inside sheet metal trunk lines insulates and absorbs fan noise in offices, schools, and light commercial buildings. Adhesive and mechanical pins secure the liner so airflow does not lift or erode the surface.
Manufactured Homes
Mobile and manufactured homes use crossover ducts and floor-level return paths. Return air components and insulated flex duct fit the limited space under and between floor sections, where standard rigid fittings often do not.
Key Specifications & Planning Steps
R-Value and Thickness
Duct insulation R-value measures resistance to heat flow and depends on material and installed thickness. Under IECC Section R403.3.1, attic ducts 3 in. and larger require at least R-8, and smaller ducts R-6. The 2021 edition applies these values to all ducts outside conditioned space, which makes R-8 duct insulation the common choice for attic supply runs. Confirm the edition your jurisdiction has adopted.
Sizing, Sealing, and Support
Measure duct diameter or width and height before ordering, and allow for overlap at seams. Seal joints with mastic or UL 181-listed tape first, since insulation does not stop air leakage. Space hangers to prevent sag, and use wide straps on wrapped duct to avoid compressing the insulation.
Choosing the Right Duct Insulation & Accessories
Start with location when selecting duct insulation. Attic and crawl space runs need faced wrap, duct board, or insulated flex duct rated to the required R-value. Runs inside conditioned space may not need insulation unless condensation or noise is a concern.
Next, match the product to the duct construction: wrap for the exterior of metal duct, liner for interior noise control, and duct board for fabricated trunk systems. Size duct dampers to the branch duct diameter.
Finally, plan the full run from plenum to register boots, so every connection, support, and sealing item arrives with the air duct insulation.
Frequently Asked Questions
Can I buy duct insulation and ductwork parts like plenums, start collars, and register boots in one order?
Yes. This category groups duct insulation with hvac ductwork supplies, including plenums, start collars, metal duct pipe, fittings, register boots, and support hardware, so insulation and components for the same run can be ordered together.
What duct accessories do I need to set an air handler on a stand and run new supply ductwork?
A typical run uses an air handler or furnace stand, a supply plenum, start collars, metal duct pipe or flex duct, elbows and other fittings, register boots, hangers or straps, and mastic or foil tape. Add insulation to any section outside conditioned space.
Duct board, duct liner, or duct wrap: which should I use for supply ducts in an attic?
Duct wrap insulates the outside of metal duct. Duct board is both the duct and its insulation, fabricated into rectangular trunks. Duct liner goes inside metal duct and is used mainly where noise control matters. For attic supply runs, wrap or duct board rated to the required R-value are the usual choices.
Is R-6 or R-8 duct insulation better for ducts in an unconditioned attic?
R-8. IECC Section R403.3.1 requires at least R-8 for attic supply and return ducts 3 in. and larger, and R-6 for smaller ducts. Confirm the code edition adopted in your area.
Should I use flex duct or metal duct pipe for branch runs to register boots?
Metal duct pipe has a smooth interior with lower airflow resistance and holds its shape over longer runs. Flex duct routes around obstructions and suits short connections. Keep flex duct fully extended and supported, since sags and tight bends reduce airflow.
How do I stop condensation on AC ducts in a hot, humid attic?
Seal all duct joints first, then insulate with faced ductwork insulation that has a continuous vapor retarder. Tape every seam and penetration in the facing so humid attic air cannot reach the cold duct surface.
What holds duct liner in place inside sheet metal duct?
Duct liner is secured with adhesive plus mechanical fasteners, such as weld pins or insulation pins with retaining washers, placed at the spacing the liner manufacturer specifies.
How do I fix a room that gets too little airflow from the HVAC system?
Check the branch for disconnected, crushed, or kinked duct first. Then adjust duct dampers on the other branches to direct more air toward the low-flow room.
How should I seal leaky duct joints before insulating them?
Clean each joint and apply mastic or foil tape over the seam. Choose an hvac duct sealant or tape listed to UL 181A or UL 181B for the duct type, and let mastic cure before insulating.
How do I support long runs of insulated ductwork so they don't sag?
Hang runs with straps or hangers at the intervals set by the duct manufacturer and local mechanical code. Use wide straps or saddles on wrapped or flex duct so the support does not compress the insulation and lower its R-value.
What type of insulation is best for HVAC ducts?
It depends on the duct. Faced fiberglass wrap suits the outside of metal duct, duct board suits fabricated rectangular systems, and duct liner suits interior insulation with noise control. Choose the type that reaches the required R-value for the duct's location.
How thick should duct insulation be for ducts in a crawl space?
Thickness follows the required duct insulation R-value, not a fixed measurement. Earlier IECC editions require at least R-6 for ducts 3 in. and larger outside attics, while the 2021 edition requires R-8 for those ducts anywhere outside conditioned space. Check the installed R-value on the product label.
Should ducts that run through conditioned space be insulated?
The energy code generally does not require insulation on ducts fully inside conditioned space. Insulation can still help where cold supply ducts pass through humid areas or where fan noise is a concern.
What parts do I need to replace the return air setup in a mobile home?
Measure the size and location of the existing return opening, then select mobile home return air components sized to fit. Seal each connection with mastic or listed tape so the return does not draw air from under the floor.
What are vane and rail systems used for in rectangular ductwork elbows?
Vane and rail systems mount curved turning vanes across square-throat elbows in rectangular duct. The vanes guide air through the turn, which lowers pressure loss and noise compared with an elbow without vanes.
