Metal And Flexible Duct Systems Impacts Upon Cooling Energy And Performance

Secondary Author(s)

Martin, Eric; Bonilla, Nicholas

Report Number





Ducts; Air Flow; Residential; Buildings; Air Conditioning


Flexible duct is commonly used throughout the U.S. in residential construction. It performs well when installed in accordance with industry standards, however, they are often not installed as such. Issues such as not cutting ducts to the exact length needed, and instead using significantly more duct, result in compression and higher static pressure. Poorly supported ducts or turns without proper radius also increase static pressure. A research project was completed to evaluate the differences in performance between a metal duct and flexible duct systems in two side-by-side otherwise identical residential laboratories. Testing evaluated three different flex duct system configurations compared to one metal duct system. The metal duct was installed to represent good practice. Flexible duct tests were run with flex installed with good practice (Test 1), with very high static pressure of 1 in WC (Test 2), and with an elevated pressure of 0.82 in WC (Test 3). While the last two tests are higher than what is typically the upper limit for air handler manufacturers, research in real homes shows it is common for high static pressures. This research report produces findings on the energy increase from specific higher static flex duct configurations as well as the importance of not over-compressing the exterior insulation and vapor barrier wrap around the metal duct system.

Date Published



Buildings - Air Conditioning; Buildings - Air Flow; Buildings - Ducts; Buildings - Residential

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