Materials & Properties
Metal gauges, material properties, galvanic corrosion, galvanized steel, aluminum, copper, and stainless steel.
- Explain the gauge numbering system and which gauge is thicker
- Describe galvanic corrosion and how to prevent it
- Identify the properties of galvanized steel, aluminum, copper, and stainless steel
- Explain springback and its effect on bend accuracy
- State the factors that determine minimum bend radius
Lesson 1
Metal Gauge & Thickness
Understanding Gauge
The gauge system measures sheet metal thickness. The critical exam fact is: 18 gauge metal is thicker than 26 gauge. In the gauge system, lower numbers mean thicker metal.
The standard gauge thickness for residential HVAC ductwork is 26 gauge for round duct and 26-24 gauge for rectangular duct depending on the duct size. As duct dimensions increase, thicker (lower gauge) material is required.
| Gauge | Thickness (inches) | Common Use |
|---|---|---|
| 30 | 0.012 | Light flashings |
| 26 | 0.018 | Residential duct, flashings |
| 24 | 0.024 | Commercial duct, roofing |
| 22 | 0.030 | Heavy duct, equipment |
| 20 | 0.036 | Industrial duct |
| 18 | 0.048 | Heavy fabrication |
Exam Trap
The exam will ask "Which is thicker: 18 gauge or 26 gauge?" The answer is always 18 gauge. Remember: lower gauge number = thicker metal.
Lower gauge numbers mean thicker metal - 18 gauge is thicker than 26 gauge. Standard residential ductwork uses 26 gauge galvanized steel. As duct size increases, thicker gauges are required.