The State of Fiber, Spiral, and Flexible Ducts in HVAC
All three types of ductwork have clear, defined roles within the HVAC ductwork landscape
MANY OPTIONS: There is great optimism throughout the industry for the future of fabric ductwork due to its ability to retain paint, health benefits, and lightweight structure.
VERSATILE FABRIC: Fabric ductwork is recognized for its ability to evenly disperse air along the entire length of a system, eliminating hot spots and cold spots in a room.
A CHANGING MARKET: Ductless mini spits and variable refrigerant flow (VRF) systems have reduced the need for traditional ductwork over the past few years.
Research from the U.S. Department of Energy (DOE) has consistently shown about 30-40 percent of the air traveling through ductwork leaks, and if air is being pulled from somewhere, like a dirty crawlspace, it is going to effect IAQ. Insulating ductwork has become a common practice for contractors across the country.
With factors like that in mind, the importance of quality ductwork is never going to diminish, which makes it all the more intriguing to see the current state of this essential segment of the HVAC marketplace. Fiber, spiral, and flexible ductwork have each carved out important pieces of the duct puzzle with each demonstrating clear benefits and noticeable drawbacks.
FIBER DUCTWORK
“Fiber ductwork is definitely continuing to grow and emerge throughout HVAC,” said Nick Kaufmann, director of manufacturing and engineering, DuctSox Corp. “One of the main things that has probably happened in the last five years is changes in code compliance itself. Five years ago, all the codes revolved around trying to match up to the smoke and flame test of UL 723, but since that time, UL has adopted its own code specifically for fabric ductwork, UL 2518. Beyond those standards, the tests include high pressure, erosion, humidity, high temperatures, etc. It’s evolved to its own standard that we must meet. When that happened, competitors started to fall off the grid. Those who really wanted to be in the market found their footing and dug in their heels.”
Kaufmann believes one of the biggest strengths of fabric ductwork comes down to even air dispersion.
“Fabric ductwork provides even air dispersion along the entire length of a system, so there are no hot spots and cold spots in a room,” he said. “That helps occupant comfort and delivers an overall better system. On top of that, it’s hygienic. Here at DuctSox, we do have a variety of colors, so paint isn’t chipping off of it, and it’s lightweight.”
He added that the acceptance of fiber ductwork has been a big game changer over the last five years.
“I’ve been in the business for close to 20 years, and when I started out, people just weren’t familiar at all with fiber ducts,” Kaufmann said. “Now, everyone understands it and accepts it as a standard. Really seeing some of the longevity that we have with fiber products is huge. People have gotten over the misconception that it is a temporary fix.”
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SPIRAL AND FLEXIBLE DUCTWORK
M&M Mfg. Co. manufactures spiral ductwork, and Chris Van Rite, vice president of sales for the company, sees that product group as one that is certainly growing in popularity.
“Exposed spiral ducts in offices, restaurants, loft condos, and sports venues are very popular,” he said. “Double-wall insulated spiral ductwork is very popular as are noncorrosive materials, like aluminum, stainless steel, and specialty coatings, for spiral ducts.”
M&M does not manufacture flexible ductwork, but Van Rite said it continues to be popular in residential and low-pressure commercial duct applications. One thing he did note is there is a growing body of knowledge that confirms significant loss of airflow with typical installations of flexible ducts.”
In regards to both spiral ductwork and flexible ductwork — with the exception of a few seals, gaskets, and some new hangers — most of the market is somewhat stagnant, Kaufmann said.
“It’s kind of like the standard that hasn’t changed,” he said. “It is there, and it works great for certain applications, but there aren’t major changes going on.”
STRENGTHS AND WEAKNESSES
Metal ductwork’s biggest strength is perhaps its ability to be used in closed-ceiling applications. Fabric ductwork is somewhat limited to open-ceiling architecture and can’t be used behind a wall or in a closed ceiling.
“Residential ducts are typically round or square sheet metal, flexible duct, or duct board,” said Van Rite. “Sheet metal ducts offer the most efficient airflow and IAQ due to the smooth surface and the fact that sheet metal ducts are easiest to install in a straight line. The problem with sheet metal ducts is they take a higher level of skill to install, and each joint and seam has to be sealed, which takes more labor. Sheet metal ducts have a smooth surface, which moves air and sound very efficiently.”
He added that flexible ducts are capable of delivering acceptable airflow, but the installer too often doesn’t cut off the excess duct and instead installs the piece he has, which causes compressing, excessive lengths, and significant pressure loss.
“Due to the spiral helix core, a flexible duct does not move air as efficiently as sheet metal duct, but it is cheaper, easier, faster, and they takes a lower skill level to install,” said Van Rite.
M&M offers factory-sealed fittings in an effort to save time and guarantee better sealed duct installations. The company also offers sealed connections for commercial rectangular and spiral ducts.
“ASHRAE is pressing for all ducts to be sealed even in conditioned space,” continued Van Rite. “M&M offers solutions for all types of sealed ducts. Contractors should be aware of these options as they can save a great deal of time and labor on the installation and guarantee a higher level of certainty that the ducts will pass pressure testing.”
TIPS AND HINTS
Kaufmann said the biggest tip he can provide contractors is to look at the full picture before making a decision on ductwork.
“There are a lot fewer steps to installing fabric ductwork than there are with metal ductwork,” he said. “When getting fabric ducts, or any duct, it’s important to look at the entire picture and see what is provided, because just looking at the metal itself is just a small portion of everything you need.”
When it comes to residential duct systems, Van Rite believes the installed airflow is typically not close to the designed airflow because contractors don’t routinely measure airflow to confirm. Therefore, they don’t know what the system is delivering.
“There are many new, affordable ways to measure airflow in the field, so contractors should always measure airflow and make the appropriate corrections when needed,” he said. “Contractors should always measure airflow on changeout systems. Old ducts will not be sealed and are likely under-insulated. These are two huge reasons to rework or replace duct systems when the equipment is being replaced.”
BEWARE OF LOW-COST, UNLIMITED, DUCT-CLEANING SCAMS
Each day, the media is filled with ads for duct cleaning companies insisting consumers need their ductwork serviced ASAP. They even provide “evidence” of homes that didn’t clean their ducts and are paying the price. How can homeowners tell if their residences need this service or if a local company is trying to charge for unnecessary sub-standard work?
According to Andrea Hughes, director of operations at Ductz of N. Lauderdale and Pompano Beach in South Florida, and a featured speaker at ACCA’s Business Technology & Operations Forum (BTO) in October in New Orleans, there are three simple steps both homeowners and businesses can follow to determine if their ducts need cleaning:
- Check the filter to see if it is clogged or blowing dirty air;
- Listen to the blower motor for any noise besides the motor; and
- Take a good look at the vent to see if dirt comes out when it is turned on.
“Duct cleaning is vital to keeping both the HVAC system and the people relying on the system healthy and functioning properly,” Hughes said. “Duct cleaning, more often than not, comes into the picture in the event of water damage and/or mold contamination. In many states, IAQ, mold, and water damage assessors practice a detailed protocol to ensure the air conditioning and duct system is cleaned, encapsulated, or replaced depending on the contamination level. These licensed assessors include hiring various remediation contractors that are licensed to ensure the interest of the homeowner as well as the integrity of the remediation.”
In order to avoid being taken advantage of by contractors, Hughes lists these important items to ask for when deciding on a company to service a home or business:
- Verify the contractor is National Air Duct Contractors Association (NADCA)-certified;
- Make the company service the entire heating and cooling system and not just the ducts;
- Don’t trust a business that charges one set price without determining your needs first;
- Ask for references from actual customers and a list of their industry certifications;
- When the work is completed, ask to see photos of before-and-after results; and
- If the cleaning company suggests sprays or sealants to clean the ductwork, ask about other cleaning methods they perform. Sealants aren’t the best solution if the property is not airtight, and many sprays are harmful to the health of individuals.
Publication date: 9/18/2017
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