HVAC Sheet Metal and Fabrication

Question 1

What is the most common gauge of galvanized sheet metal used for residential ductwork?

Accepted Answer

26 gauge (0.018")

Answer

26 gauge galvanized steel is the standard for most residential ductwork, providing adequate rigidity for typical residential pressure classes.

Question 2

What is the purpose of 'seam' construction in sheet metal ductwork?

Accepted Answer

To join the longitudinal edges of sheet metal to form a duct shape, providing structural strength and airtight construction

Answer

Longitudinal seams join the two edges of flat sheet metal to form rectangular or round duct sections, providing structural rigidity and, when properly formed, airtight joints.

Question 3

What is 'Pittsburgh lock' seam and when is it used in ductwork fabrication?

Accepted Answer

A longitudinal seam type using a rolled mechanical lock; standard for rectangular ductwork fabrication

Answer

The Pittsburgh lock is a longitudinal seam where one edge is formed into a 'Pittsburgh' channel profile and the other edge is inserted and crimped over—the standard seam for mechanically formed rectangular ductwork.

Question 4

What is the difference between 'transverse' and 'longitudinal' joints in ductwork?

Accepted Answer

Transverse joints run across the duct (connecting duct sections end-to-end); longitudinal joints run along the length of a duct section (forming the duct shape from flat sheet)

Answer

Transverse joints connect individual duct sections end-to-end; longitudinal seams form the duct shape by joining edges along the duct's length.

Question 5

What is 'TDF' (Transverse Duct Flange) connection?

Accepted Answer

A rolled flange formed on the duct end that accepts a flange connector (clip), providing airtight, rigid connections faster than slip-and-drive for commercial ductwork

Answer

TDF uses a formed flange rolled into the duct end, connected with corner clips. It provides faster installation, more airtight joints (with gasket), and greater structural rigidity than traditional slip-and-drive connections.

HVAC Practice Test

HVAC Practice Test

HVAC Sheet Metal and Fabrication