Round, spiral duct sets the standards for duct production and installation efficiency, many experts say. No other production method is as efficient to produce or has as low a ratio of duct material to airflow capacity.

The use of an engineered connecting flange system like the Metu-Streimer MF Flange with SR joining clip can lead to even more savings from both an installation and a system design perspective, the manufacturer says.

The three-piece MF Flange system for round ductwork provides installation benefits for both positive and negative pressure systems. The MF Flange system uses just one bolt to connect the two pieces of duct. The SR joining clip, together with the MF flanges, provides a three-piece connection system that significantly reduces labor costs during installation. The labor to install the flanges occurs in a sheet metal shop, under controlled conditions. Once the product reaches the field, it is installed quickly, minimizing labor and reducing the time spent on a ladder tightening bolts or driving screws.

An engineered flange system can also provide significant system design benefits for negative pressure systems, company officials add. The use of the MF Flange system can enable the use of spiral duct in larger diameters for a negative pressure class system.  For example, in a negative 4-inch water-gauge system, 48-inch diameter round spiral duct is not approved for use without reinforcement based on the Sheet Metal and Air-Conditioning Contractors’ National Association’s HVAC construction standards for metal and flexible ductwork. However, if MF flanges and SR joining clips are used, a standard 10-foot section of round duct can be made from 22-gauge spiral.

Lightening the load

Use of the MF Flange system can also enable lighter-gauge metal to be used with spiral duct. In some cases, the cost savings for a lighter-gauge metal can offset the cost of both the flanges and SR joining clip. Consider a 40-inch-diameter piece of round spiral duct that is 10 feet long and designed for use in negative 4-inch water gauge, the unstiffened duct would need to be made of 16-gauge galvanized steel. When the MF flanges and SR joining clip are used, this same piece of duct can be made of 24-gauge galvanized steel. This savings in material cost is significantly greater than the price of the flange system.

This table can be used in combination with the SMACNA negative pressure-class tables for round spiral duct to design a system that minimizes both material costs and assembly costs in the field.

Metu-Streimer’s newest round connecting flange, the MFH, is a hemmed flange that can be connected via screws without the use of the SR joining clip. The MFH is available in 18-gauge galvanized steel and has pre-punched pilot holes in one layer of the hem to aid in installation. The pilot holes are spaced to be suitable for all pipe sizes from 20 to 60 inches

More information about Metu-Streimer systems is available online at

This article and its images were supplied by Metu-Streimer.