In most older homes and many newer homes, metal ductwork carries hot or cold air from the HVAC equipment to rooms throughout the house. Most of the time, homeowners pay little attention to their ductwork as long as the HVAC equipment itself is working and the indoor environment remains comfortable.

But what homeowners don’t realize is that their ductwork could easily be leaking one-third or more of that conditioned air into the attic or building envelope before it ever reaches its final destination. The result is an HVAC system that works harder and longer, and consumes much more energy, in order to heat and cool a home.

And while some model building codes now require duct-leakage testing and sealing, there is still a significant amount of work to be done — and a significant amount of energy to be saved.

Losing Energy

Sam Rashkin, chief architect of the Building Technologies Office in the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy, pointed out that the HVAC system in the majority of older residences is the biggest single energy consumer in the home, accounting for as much as half of a home’s total energy usage. That, coupled with the fact that the average home’s ductwork leaks like a sieve, is a recipe for major energy loss, he said.

“It’s a big deal when the ducts leak. Basic research from DOE uncovered that about 30-40 percent of the air traveling through ducts leaks,” Rashkin said. “If they’re pulling air from a dirty crawlspace, that’s going to affect the IAQ. It introduces dust and bugs. It’s not just energy — it’s comfort and durability.”

The problem, Rashkin said, is that when homes were constructed in the past, very little attention was paid to the ductwork. And while it has gotten slightly better in the past decade or so, especially with building codes in some states requiring duct leakage testing and very low leakage rates in new homes, most states have yet to adopt such strict codes.

Bob Reid, technical director for the Spiral Duct Manufacturers Association (SPIDA), added that without proper enforcement, such building codes will not be very effective.

“The problem is that stricter standards are going to be enforced first on the people who are already doing quality, high-end work and have high expectations,” Reid said. “They’re going to latch onto the new standard, but until it starts getting applied across the board, it’s not going to clean up the industry. And that’s what we’re working on.”

Testing Ductwork

To reduce duct leakage, contractors first need to find out how much air the ductwork is leaking, and from where. Reid said it can be as simple as going up into the attic or crawl space and poking around. “Quite honestly, when you have a system that’s leaking 30 percent, you can usually feel the leaks,” he said.

Smoke pens can also be used to track air movement near the ductwork, and soapy water sprayed on the joints can help make leaks apparent in the form of bubbles, but the most accurate way to test for duct leakage is by sealing up the registers and using a duct blaster to pressurize the system and measure the air leakage.

“The duct blaster test is the recognized standard for leak testing,” said Chris Van Rite, vice president of sales for M&M Manufacturing Co., Fort Worth, Texas. “When done properly, this is an excellent test for demonstrating how well the system is sealed.”

To help contractors accurately test for duct leakage, the North American Insulation Manufacturers Association (NAIMA) recommends that duct systems “be tested by a qualified individual using standard duct testing methods such as the Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) ‘HVAC Air Duct Leakage Test Manual.’”

Inspecting and testing the ductwork for leaks and other issues should always be done before installing any new equipment, added Gregg D’Atille, owner of Art Plumbing and Air Conditioning, Coral Springs, Fla.

“The contractor has to be in the mindset of wanting to deliver total comfort, and they have to be able to look at the whole home as a system, not just two shiny boxes,” D’Atille said. “Unfortunately, some contractors only care about putting in two new shiny boxes and getting in and out of that job. What good is putting high-efficiency equipment into ductwork that’s up to 40 years old that was never built to handle the cfm or the efficiency of the new equipment?”

Seal It Up

If the contractor determines a building’s ductwork is leaky, it needs to be addressed before a new heating or cooling unit can be installed, D’Atille said, drawing a parallel between a home’s HVAC system and the human vascular system. “Your air conditioner or furnace is like the human heart, and the ductwork is the artery,” he explained. “You can’t put in a new heart if the artery is blocked, dirty, or leaking.”

To seal ductwork, there are several options available, including rolled mastic sealant, spray sealant, and other brush-on sealants that can be applied to the exterior of the ductwork by hand.

“I can buy a half gallon of duct sealant for $12.99, and that will seal 75 linear feet of seams that are leaking,” Reid said, adding that an infrared thermometer, which can be used to detect leaks along the duct-work, can be purchased for $30 at the hardware store. “In two or three hours, I could cut duct leakage from 30 percent to about 4 percent.”

“M&M uses mechanical sealing when possible and spray mastic by Hardcast for joints and seams we can’t seal mechanically,” Van Rite said. “We use a latex-based product that stays pliable after cured. This ensures that the seal won’t be compromised by rough handling or expansion and contraction.”

From the Inside Out

Rashkin said hand sealing ductwork is most common, though leaks can also be patched automatically with a system like Aeroseal — a non-toxic aerosol sealant that patches the ductwork from the inside out.

“A system like Aeroseal can find all the cracks and holes and fill them automatically,” Rashkin said.

The product is gaining steadily in popularity as more and more contractors sign up to be Aeroseal contractors, and recently, the company rolled out its HomeSeal system, which is specifically designed for the residential market.

“We block off all the registers so there’s nowhere for the aerosolized mist to go but through the holes in the ductwork,” explained Neal Walsh, vice president of sales and marketing at Aeroseal. “Then we inject the aerosol into the duct system. It travels through the duct and to the hole, and the sealant sticks around the edge of the hole. It’s like blood clotting.”

For Steve Tansey, owner of Arrowseal in Prescott Valley, Ariz., Aeroseal projects brought in so much business that he now concentrates solely on duct sealing. The average customer, he added, ends up saving $40 per month on their electric bill as a result of duct sealing.

“The one thing that makes this a success is that it works,” Tansey said. “It’s something that when you say you’re going to better someone’s life and save them energy, there’s no doubt about it.”

D’Atille has also had success with Aeroseal. “We’ve had rave reviews from our customers on performance and lower electric bills,” he said. “We had one customer that was losing almost 350 cfm to leaky ducts, and we got it down to 30 or 40 cfm.”

No Time to Waste

Not sealing ductwork can not only affect system efficiency, but also IAQ, Van Rite said.

“First, we lose the energy that has been invested to remove the heat and moisture from the air, and second, we create a negative pressure in the conditioned space that tries to equalize itself by sucking in hot, moist, dirty outside air from around doors and windows and anywhere the house leaks. This adds to the load on the system and clogs filters and coils.”

Even though the many benefits of duct sealing are well documented, getting the word out to customers is still proving to be difficult.

“There’s a lack of consumer education,” Reid said. “Homeowners don’t care about the ductwork, and nobody is going to buy a house based on whether it has good ductwork.”

Reid added that more information in the form of independent studies could help bring attention to the problem. “There has to be an outside push to get some of this stuff happening, but there’s still so much that needs to be done. Who’s going to make it happen?”

Rashkin agreed with Reid that duct leakage is a significant issue that needs to be addressed in the United States.

“This isn’t trivial — this is very important,” he said. “Since well over 95 percent of older homes have leaky ducts, it’s something that’s relevant for almost everybody.”

Publication date: 10/21/2013

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