HVAC uses of flexible air duct have grown exponentially over the last two decades, all over North America. Contractors and installers say they like it, even find it indispensable. It has changed the way architects design residential construction and how they engineer tall buildings, offices, stadiums, stores, factories, hospitals, schools, and shopping malls.

"Flex" has created the "technical home" whose appearance, roominess, and comfort - supported by technology - have changed traditional, centuries-old thinking about how we heat and cool dwellings and other buildings.

Believer In Arizona

For instance, John Van Asdlan, product manager for Rite-Way Ventilating in Tucson, Ariz., is a firm believer in flex duct. He has been installing mechanical systems for the past 30 years.

"I did my share of large commercial jobs, as well as several large tract developments. We used flex in all of these projects," he said.

Now, he concentrates 99 percent on new residential construction, mostly tract homes that continue to advance out into the desert terrain, both northwest and southeast of his city.

"The old, Santa Fe colonial-style house with its flat roof and seven-foot, fur-down, soffit construction has been replaced almost entirely," he said.

Builders, hoping to add some volume to their 1,600-square-foot to 2,000-square-foot entry level homes in the southern Arizona desert, adopted 13-foot vaulted ceilings to create the effect of extra space that people moving from California and the East were used to.

"It used to be, in residential construction, that you built the house around the mechanical system, with its rectangular-shaped hard ducts in soffits. Now, the mechanical system has to be installed around the house," said Van Asdlan.

The Tucson contractor "likes the flexibility" of the flex air duct. It bends easily around fixed structures in an attic, and the builder/contractor is not constrained by the rectangular soffit shape of hard, sheet metal air duct.

Building insulation standards have changed, too.

"We used to work above the batt (ceiling insulation) in the attic. Now, we work below the batt (roof insulation)," he said.

That change cuts costly heat transfer and enhances the longevity of the flex duct by providing a more temperate operating environment for it, Van Asdlan explained. It also cuts the cost of energy for the homeowner, he said.

"You can pull flex through the various web truss openings, get inside of vaulted ceilings, and still handle more cubic feet of air."

Quality Improvements Recognized

The Tucson production manager remembers the early days of flex when plastic jackets would deteriorate as oils in the plastic leached out.

"In the bad old days, flex sometimes fell apart, except for the insulation," he said.

Today, Van Asdlan sees a much-improved flex quality. Scrim foil backing is now impervious to heat, he said.

"Now, we also increase the R-value factor to R-6 or R-8 to reduce the cost of heating and cooling," he said. "This contributes to increased efficiency of the HVAC system, which is another way that homeowners measure quality.

"Labor savings; eliminating different sizes and fittings for hard ducting; ruling out certain custom-fabrication concerns; using specially-designed ‘T' and ‘Y' branches and tapered floor boxes - all of these contribute to the benefits of flex. You can accomplish the same results with flex that you can with hard ducting. If you want to keep up with the game, you've got to use it.

Fast, Easy To Install

Estimator Reggie Olney, of Greg's Heating and Air Conditioning in Orland, Calif., echoes some of the reasons his firm uses flex in their HVAC projects.

"It's flexible versus rigid, which eliminates fabricating elbows. It's economical to install, and it has integral insulation in its design," said Olney. "You can estimate needing roughly half the time to install flex duct than hard pipe.

"You run it straight, and it's done. We teach our guys to do nice, straight, clean runs with no airflow restriction."

In a business that is 80 percent residential and 20 percent light commercial construction, Olney maintained there is "less labor" in using flex.

"I've had no trouble with it in 14 years," he said.

Greg's Heating and Air Conditioning normally uses hard pipe for the main air handler and adds flex as the last seven feet to the air grilles in a commercial job. A local Distance Learning Center, the College of Siskiyous Junior College, upgraded its air handler and replaced hard pipe with more flex (5- to 7-foot runs) to dampen noise. Teachers at the college said that it provided a quieter environment for beaming their course work from studio classrooms to home computers, Olney reported.

Author Stephen J. Colvin is a freelance writer from Arlington Heights, Ill.

Sidebar: Air Diffusion Council Supplies Guidance

Not every homebuilder or HVAC contractor believes that you should string flex "like spaghetti." Un-workmanlike installation can lead to problems, including air pressure drops, improper ventilation, and an unbalanced (or under-performing) HVAC system.

Eliminating these "uns" has been the job of the Air Diffusion Council (ADC), a trade association representing flexible air duct manufacturers across North America, headquartered in Schaumburg, Ill.

"We want to call attention to proper installation of flex," said executive director Jack Lagershausen. "Early in 2004, ADC will introduce its fourth edition ‘Green Book.' This up-to-date reference leads contractors and installers through proper installation techniques, step by step. Architects and specifying engineers, code bodies, builders, contractors, and installers - everyone who has a hand in HVAC systems - should have the latest edition."

ADC's Green Book, which will be available in a 28-page printed version or on CD-ROM - both for the same price of $15 - is designed to offer easy-to-follow illustrations on how to handle, hang, bend, splice, tape, and fasten flex to its terminal outlet.

For more information, contact ADC at www.flexibleduct.org.

Publication date: 12/01/2003