This guide covers everything you need to know about Round Duct Fittings. Key takeaways: detailed specifications, cost comparisons, pros and cons, maintenance requirements, and expert recommendations from Preda Machine — a leading HVAC duct machinery manufacturer since 2008, serving 60+ countries.
In This Guide
Types of Round Duct Fittings
| Fitting Type | Function | Pressure Loss (C) | Fabrication Difficulty |
|---|---|---|---|
| 90° Elbow (gored) | Change direction 90° | 0.25-0.45 | Medium |
| 45° Elbow | Change direction 45° | 0.12-0.20 | Medium |
| Tee (straight) | Split airflow straight | 0.15-0.30 | Medium |
| Tee (branch) | Split airflow to branch | 0.30-0.60 | High |
| Reducer (concentric) | Change duct size | 0.05-0.15 | Low |
| Reducer (eccentric) | Change size offset | 0.08-0.20 | Medium |
| Takeoff (saddle) | Branch from main duct | 0.20-0.50 | High |
| End cap | Seal duct end | N/A | Low |
| Cross | 4-way connection | 0.30-0.70 | High |
Elbows and Bends
Round duct elbows are typically fabricated using the gore method — cutting wedge-shaped gores from flat sheet and rolling them into curved sections. The number of gores determines the smoothness of the bend:
| Elbow Type | Gores per 90° | Radius (× diameter) | Pressure Loss (C) |
|---|---|---|---|
| Short radius | 3 gores | 1.0D | 0.45 |
| Medium radius | 5 gores | 1.5D | 0.30 |
| Long radius | 7 gores | 2.0D | 0.20 |
| Smooth bend | 9+ gores | 2.5D+ | 0.15 |
A gorelocker machine (also called an elbow machine) automates the process of cutting and forming gores, reducing fabrication time from 30 minutes per elbow to 3-5 minutes. Preda Machine offers both electric and hydraulic gorelocker models for duct diameters 80-1600mm.
Best Practice
Use 5-gore elbows with 1.5D radius as the standard for commercial HVAC. They balance pressure loss (C=0.30) with fabrication cost. Short-radius 3-gore elbows should only be used in tight spaces where a longer radius won't fit.
Tees and Takeoffs
Straight Tee
A straight tee has the branch entering the main duct at 90°, with a smooth internal transition. The straight-through path has low pressure loss (C=0.15), while the branch path has higher loss (C=0.30-0.60) due to the 90° turn.
Wye Tee (45° Branch)
A wye has the branch entering at 45° instead of 90°, significantly reducing branch pressure loss (C=0.20-0.35). Wyes are preferred for balanced systems but require more space and are more expensive to fabricate.
Saddle Takeoff
A saddle takeoff is a branch connection that wraps around the main duct like a saddle. It is cut into the main duct on site and attached with screws and sealant. Saddle takeoffs are flexible but have higher pressure loss and leakage potential.
Reducers and Transitions
| Reducer Type | Length (× diameter) | Pressure Loss (C) | Application |
|---|---|---|---|
| Concentric (short) | 1.5D | 0.15 | Space-limited |
| Concentric (standard) | 3.0D | 0.08 | Standard |
| Concentric (long) | 5.0D | 0.05 | Low noise |
| Eccentric (flat) | 3.0D | 0.10 | Ceiling installation |
Concentric reducers have the centerline aligned, making them ideal for vertical ducts and symmetrical layouts. Eccentric reducers have one flat side, used when the duct must run flush with a ceiling or floor. Always use a reducer length of at least 3× the diameter difference for minimum pressure loss.
Pressure Loss Coefficients Reference
| Fitting | Coefficient (C) | Equivalent Duct Length |
|---|---|---|
| 90° elbow (5-gore, 1.5D) | 0.30 | 15 ft (4.5m) |
| 45° elbow | 0.15 | 7 ft (2.1m) |
| Tee (branch flow) | 0.45 | 22 ft (6.7m) |
| Tee (straight flow) | 0.15 | 7 ft (2.1m) |
| Wye (branch) | 0.25 | 12 ft (3.7m) |
| Concentric reducer | 0.08 | 4 ft (1.2m) |
| Saddle takeoff | 0.40 | 20 ft (6.1m) |
| Round-to-rectangular transition | 0.20 | 10 ft (3.0m) |
Total system pressure loss = sum of all fitting losses + straight duct friction loss. Fittings typically account for 50-70% of total pressure loss in a well-designed duct system.
Fabrication Equipment
| Equipment | Produces | Capacity | Price Range |
|---|---|---|---|
| Electric gorelocker | Elbows, gores | 80-800mm | $3,000-$6,000 |
| Hydraulic gorelocker | Elbows, gores (heavy) | 200-1600mm | $6,000-$12,000 |
| Plasma cutter | Custom fittings, patterns | Any shape | $5,000-$15,000 |
| Slip roll | Round bodies, reducers | 1.5mm × 1300mm | $1,000-$3,000 |
| Spot welder | Assembly | 1.5mm | $800-$2,000 |
For a complete round duct fitting shop, the essential equipment is: spiral duct machine + gorelocker + plasma cutter + slip roll + spot welder. This combination produces all standard round duct and fittings with minimal manual labor.
Frequently Asked Questions
Preda Care: After-Sales That Never Expires
When you invest in HVAC duct manufacturing equipment, downtime costs money. With Preda Care, you get lifetime technical support — not just during warranty, but for the entire life of your machine. Our global agent network provides local service in 40+ countries.
- 24-hour response time
- Free spare parts shipping
- Remote PLC program support
- Global agent network
- Video call troubleshooting
- On-site installation
Need Equipment Recommendations?
Tell us your duct specifications, daily production volume, and workshop size — our engineers recommend the perfect equipment configuration within 24 hours.
Get Free Consultation