HVAC Duct Fittings

Complete your duct system with precision-fabricated fittings for round, square, and rectangular ductwork. Made-to-order in galvanized steel, aluminum, or stainless steel — SMACNA compliant and built to connect with your existing system.

20 products

Every Fitting Your Duct System Needs — Built to the Same Standard as Your Duct

A duct system is only as tight as its weakest fitting. Poor-quality elbows, reducers, and transition pieces create air leakage, increase static pressure drop, and reduce system efficiency — leading to comfort complaints, energy waste, and code violations on pressure-tested systems. Every fitting in the Duct2Go catalog is fabricated to SMACNA standards using the same gauge sheet metal and seam construction as our duct sections. This means consistent sizing, compatible gauges, and joints that seal without excessive tape or mastic.

Our fittings catalog covers the most common connection scenarios in residential and light commercial systems: 45° and 90° elbows in both round and square profiles, conical reducers for stepping down between diameters, spin-in taps for adding branch connections to spiral or round trunk lines, flex connectors for isolating air handler vibration, end caps for terminating runs, and square-to-round transitions for connecting rectangular trunk sections to round branch runs.

Square to Round Duct Transitions — A Critical Connection Made Right

The square-to-round transition is one of the most frequently specified fittings in HVAC system design. It connects a rectangular trunk line to a round branch duct, allowing airflow to change cross-sectional shape without significant pressure loss — when sized correctly. Undersized or poorly fabricated transitions create turbulence, noise, and energy loss that no amount of balancing can correct.

Our square-to-round transitions are available in standard configurations and can be custom-fabricated to match any rectangular outlet and round branch diameter combination. If you are not certain what size you need, contact our team with the rectangular duct dimensions and the required round branch diameter — we can confirm the correct transition geometry for your system.

Custom HVAC Duct Fittings for New Construction, Retrofit & Replacement Projects

No two HVAC systems are exactly alike, which is why standard off-the-shelf fittings do not always provide the best fit. Duct2Go manufactures custom HVAC duct fittings to match the dimensions and airflow requirements of residential, commercial, and industrial duct systems. Whether you need a conical reducer, square-to-round duct adapter, offset transition, custom elbow, or specialty branch connection, our fabrication team can build fittings to your exact specifications.

All fittings are available in galvanized steel, aluminum, and stainless steel, with dimensions produced to SMACNA standards for compatibility with existing ductwork and equipment. Contractors, HVAC installers, sheet metal shops, and facility managers rely on custom-fabricated fittings to solve field challenges, reduce installation time, and maintain proper airflow throughout the system. Upload your drawings, dimensions, or project requirements and our team will provide a fast quote for made-to-order HVAC duct fittings built specifically for your application.

Frequently Asked Questions

What types of HVAC duct fittings does Duct2Go carry?

Duct2Go carries: round 45° and 90° elbows, round conical reducers, round conical takeoffs, spin-in taps, round pipe couplings, round pipe end caps, round flex connections, rectangular straight tap takeoffs, rectangular duct end caps, square 45° and 90° elbows, square flex connections, and square-to-round transitions. All are available in galvanized steel; aluminum and stainless steel available on request.

What is a spin-in tap fitting and when is it used?

A spin-in tap (also called a spin-in fitting or saddle tap) is used to add a branch supply connection to an existing spiral or round trunk duct without cutting out a full section. You drill a hole in the duct wall and insert the spin-in fitting, which locks in place with a quarter-turn. It is the standard method for adding register drops to a spiral trunk line and is particularly useful on retrofit and remodeling projects.

What is the difference between a conical reducer and a square-to-round transition?

A conical reducer changes diameter within a round duct run — for example, stepping from a 12" trunk down to an 8" branch. A square-to-round transition changes shape — converting a rectangular duct outlet to a round duct inlet. Both are available at Duct2Go in standard sizes and custom configurations.

Are your fittings compatible with duct from other manufacturers?

Yes. All Duct2Go fittings are dimensioned to SMACNA standards, which means they are compatible with standard duct sections from any manufacturer. Confirm the nominal diameter and gauge match when mixing fittings with duct from another source and the connections will be correct.

Can I order custom-size fittings not listed in the catalog?

Absolutely. Custom fittings are a core part of our service. Unusual angles, oversized reducers, transitions between non-standard dimensions — if you can describe or sketch it, we can fabricate it. Submit your specs through the custom quote form and receive a price within one business day.