Duct Fittings
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Lukjan 4" Long Collar with Metal Damper Tab, Snap-Lock (MPN: RX1304)SKU: 2010897$15.98 20% off $19.97
Duct Fittings
Duct fittings are the precision-engineered components that determine how efficiently a forced-air HVAC ventilation system moves conditioned air from the central air handler to every room in a structure. At Plumbing Supply & More, we stock a professional selection of duct fittings from Lukjan and Deflecto — manufacturers that HVAC contractors and sheet metal fabricators rely on for consistent dimensional accuracy, durable galvanized steel construction, and field-ready performance.
Whether you are branching off a rectangular trunk duct for a new supply run, connecting round duct pipe to an existing ductwork layout, or sealing a wall cap on an exterior termination point, the correct fitting determines how accurately your system delivers its designed CFM output across every ventilation zone.
What Are Duct Fittings & Their Role in HVAC Ventilation Systems
Duct fittings are the manufactured sheet metal components that join, branch, redirect, and terminate sections of round and rectangular duct pipe within a forced-air ventilation, heating, or cooling system. They serve as the structural vocabulary of ductwork layout, allowing HVAC professionals to branch supply air from a main trunk duct into individual runs that serve specific rooms or zones.
In practical terms, a duct fitting governs the path conditioned air follows from the furnace or air handler through the entire distribution network to each supply register. Poorly selected or incorrectly installed fittings create turbulence, restrict airflow, and compromise the designed cubic feet per minute (CFM) delivery — causing rooms to receive insufficient heat in winter or inadequate cooling in summer.
The fittings stocked on this page cover the most frequently specified types in residential and light commercial HVAC work: adhesive duct takeoffs, adhesive top takeoffs, long collars with metal damper tabs, and wall caps with spring dampers. Each type fills a distinct function within the broader ductwork manufacturing and installation framework.
Lukjan Adhesive Duct Takeoffs with Damper — Side Branching for Trunk Duct & Round Duct Pipe Systems
Lukjan adhesive duct takeoff fittings are the foundation of supply air branching in residential and commercial ductwork, engineered to attach directly to the side of a rectangular trunk duct and create a round branch outlet in diameters from 4 inches through 16 inches. The adhesive base flange eliminates the need for field-cut sheet metal collars at the trunk duct wall, reducing installation time and the likelihood of air leakage at the connection point.
Each takeoff in this series integrates a built-in adjustable plate damper that allows the installer to regulate the volume of conditioned air delivered through the branch run. This is essential in multi-zone systems where heat delivery must be balanced across several supply registers, with each branch receiving its proportional share of total system airflow.
Available diameters run continuously from 4 inches through 16 inches — covering 4", 5", 6", 7", 8", 9", 10", 12", 14", and 16" — giving contractors the flexibility to match branch pipe sizing to the calculated heat or cooling load for each individual space. The galvanized steel sheet metal construction used in Lukjan manufacturing aligns with SMACNA ductwork fabrication standards for corrosion resistance and structural integrity, ensuring the fitting maintains its shape and airtight seal throughout decades of HVAC service.
Lukjan Adhesive Top Takeoffs with Damper — Overhead Branch Connections for Ceiling Supply Runs
When a supply run must exit through the top surface of a rectangular trunk duct rather than the side wall, Lukjan's adhesive top takeoff series provides a purpose-built fitting that creates a clean upward-facing round collar on the trunk duct body. This geometry is the standard configuration in systems where round duct pipe routes vertically through a wall or floor assembly before reaching a ceiling diffuser or high-wall register.
The top takeoff design shares the same adhesive base and integrated adjustable damper found in the side takeoff series, ensuring precise airflow control is not sacrificed when the installation geometry changes. Sizes in the top takeoff line run from 5 inches through 8 inches — the most common branch diameters in residential supply runs serving individual rooms, hallways, and small commercial spaces.
Proper selection between a side takeoff and a top takeoff depends entirely on the trunk duct orientation and the intended routing of the branch duct pipe through the building structure. Using the wrong fitting geometry forces an immediate bend in the branch run directly after the trunk connection, introducing resistance that reduces effective CFM delivery at the register.
Long Collars with Metal Damper Tab — Sheet Metal Precision for Round Duct Connections & Retrofit Applications
Lukjan long collars with a metal damper tab are cylindrical sheet metal sleeves designed to be inserted into a field-cut hole in a rectangular trunk duct, creating a round stub-out collar that accepts standard round duct pipe or flexible insulated duct. Unlike adhesive takeoffs, long collars rely on a tight friction fit combined with a field-applied bead of duct mastic or foil-backed tape around the perimeter to maintain an airtight seal at the trunk duct wall.
The metal damper tab integrated into each collar is a bent galvanized steel flap that rotates to partially or fully restrict airflow through the collar opening, providing a compact alternative to a full butterfly damper in locations where space is limited but airflow trimming is still required. Lukjan manufactures these collars in sizes ranging from 4 inches through 14 inches, with the 4-inch model also available in a snap-lock configuration for faster field assembly without additional fasteners.
Long collar fittings are a preferred specification among sheet metal fabricators and HVAC service technicians because they can be retrofit into existing ductwork with minimal modification. This value becomes significant when balancing or expanding a ventilation system in an older building without fully reconstructing the trunk duct layout from scratch.
Deflecto Wall Cap with Spring Damper — Exterior Duct Pipe Termination & Ventilation Protection
The Deflecto 3-1/4" x 10" wall cap with spring damper is an exterior-mounted fitting engineered to terminate a rectangular duct pipe through an exterior wall while preventing backdraft, pest intrusion, and heat loss when the ventilation fan is not running. This rectangular profile matches the standard duct cross-section used for range hood exhaust, bathroom exhaust fan venting, and similar residential ventilation applications that exit through a wall cavity.
The spring-loaded damper mechanism is the critical functional detail: the damper stays held closed by spring tension until the fan generates sufficient static pressure to push it open, at which point exhaust air flows freely to the outside. When the fan shuts off, the spring returns the damper to the closed position, blocking cold outside air from infiltrating back through the duct pipe and into the conditioned interior — a measurable contribution to building heat retention and energy efficiency.
Deflecto is an established name in residential ventilation accessory manufacturing, and this wall cap is built from materials rated for the UV exposure, precipitation, and temperature cycling that exterior installations face over years of continuous service. Proper installation includes securing the cap flange to the wall surface with corrosion-resistant fasteners and sealing the perimeter with exterior-grade caulk to prevent air and moisture infiltration between the cap and the wall cladding.
Selecting the Right Duct Fitting Size, Gauge & SMACNA Manufacturing Reference Standards
Selecting the correct duct fitting diameter is not an arbitrary choice — it is a calculation derived from the airflow requirements of the space being served, the design velocity limits of the branch duct, and the available static pressure from the furnace or air handler. Oversizing a branch takeoff draws more conditioned air than the zone requires, robbing other branches of their share, while undersizing creates velocity noise at the register and reduces comfort delivery.
The gauge of the galvanized sheet metal used in Lukjan fitting manufacturing is also a factor in long-term system performance. The gauge specifications used in Lukjan's production process align with SMACNA standards for round branch duct fittings, which define minimum metal thickness relative to diameter — a reference point that professional HVAC contractors use when specifying materials for both new construction and service replacement work.
In systems where branch runs exceed 10 feet from the takeoff to the register boot, a damper-equipped fitting at the trunk connection point becomes especially important because it allows airflow balancing at the source rather than requiring a secondary balancing damper further down the duct pipe. This is the practical engineering reason why every fitting in this collection includes a damper component.
How Dampers in Duct Fittings Regulate Heat Distribution & CFM Balance Across Ventilation Zones
Every duct fitting on this page includes some form of damper — either a metal damper tab, an adjustable plate damper, or a spring-loaded wall cap damper — because airflow control is inseparable from effective whole-system HVAC performance. A damper is not simply a shut-off device; it is the primary balancing tool a technician uses to equalize heat delivery across every supply register in a multi-room ventilation system.
In new construction, system balancing begins at commissioning, when the technician measures CFM at each register and adjusts takeoff dampers until every room receives its designed airflow share relative to its heat loss or gain calculation. In retrofit and service work, damper-equipped takeoffs allow a technician to redirect airflow from overserved zones toward underserved ones without cutting into existing duct pipe or adding new fittings downstream.
The difference between a metal damper tab on a long collar and a full adjustable plate damper on an adhesive takeoff is primarily adjustment range and control precision. Metal tabs provide coarse restriction — practical for trimming 10 to 30 percent of airflow in an already-balanced branch. Plate dampers rotate fully from wide open to fully closed, giving the installer complete authority over that branch's contribution to total system CFM.
Shop Duct Fittings at Plumbing Supply & More — Wholesale Pricing, Trusted Brands & Expert Service
Plumbing Supply & More has been a family-owned HVAC and plumbing supply house for 75 years, and this duct fittings selection reflects the same commitment to professional-grade products and wholesale pricing that contractors and homeowners depend on throughout every category we carry. Every Lukjan and Deflecto fitting here is manufactured to the dimensional and material standards that HVAC professionals reference in the field, with consistent inventory so your project is never delayed waiting for a common size.
Whether you are a licensed HVAC contractor outfitting a new construction project, a service technician balancing an existing ventilation system, or a homeowner extending a supply run to a newly finished room, this selection covers the core duct fitting types your installation calls for. Orders over $150 qualify for free same-day shipping, and our 30-day return policy provides confidence when selecting fittings for projects where exact sizing sometimes requires a reference fitting in hand before final confirmation.
Browse the full selection above to find the diameter, style, and damper configuration your ductwork requires. Our team is available to provide technical guidance on fitting selection, sizing calculations, and compatibility with trunk duct dimensions whenever you need support from a supply house that understands HVAC work from the ground up.
