A New Comfort Remedy

This time of year the airwaves are filled with ads urging you to get your ducts cleaned. Your ducts are your home's lungs, they say, so why wouldn't you clean them? Yet if comfort is a problem in your home, its more important to seal your ducts than it is to clean them up.

After years of research at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (LBNL), a new process shows real promise of permanently solving comfort-related leaking ductwork problems in many (though not all) homes. LBNL's process-called the Aeroseal systems being licensed around the country to a few experienced heating and cooling system contractors. The first Denver area company to sign up, take the training and start sealing homes is Air Flow Solutions, Inc. (303-635-1010)

The approach relies on a airborne sealant that is circulated within the ductwork. But first a little background on the basic problem.

Duct problems

Virtually every home's ductwork leaks. According to LBNL, typical duct systems lose 25 to 40 percent of the heating and cooling energy put out by the furnace or air conditioner. Field observations by contractors working with Energy Rated Homes of Colorado generally support LBNL's claim.

Ductwork leaks cause comfort problems and energy problems that you usually wouldn't tie back to ducts until they are sealed up. Leaky ducts can either cause or exacerbate premature building failures, most frequently early paint failures but sometimes more serious problems like rot. Sadly, leaking ductwork sometimes causes health and safety problems, such as the drafting of unburned combustion gases back down water heater flues and into the house air.

When ducts run through attics or vented crawl spaces, the leaking warm air in winter and cool air in summer is wasted, which drives up your energy bills. If ducts are located within basements and the house, most people think they don't have an energy problem; often that isn't true, for some pretty complex reasons. But any air leaking out of ducts, no matter where the ducts are located, means the heated or cooled air won't get to the rooms where you want it to go. So leaking ducts may be partly or largely why your upstairs is too cold in winter, why that room over your garage is never comfortable, and why air-conditioned basements can be much cooler than living spaces above during the summertime.

Duct tape not for ducts

Slap a little duct tape over those leaks and the problem is solved, you ask? Not even close. Studies done at national laboratories indicate that virtually all normal duct tapes fail over time when wrapped around ductwork. It appears the average tape's adhesive degrades with heat. So ironically, you should never use duct tape on ductwork.

If your ducts are accessible, you can seal up gaps with mastic-a permanent sealant with the consistency of peanut butter that is swabbed on with a disposable paint bush. Available at Home Depot for $16 per gallon bucket, mastic is messy but permanent. With conventional mastic, however, the big "if" is access to the ducts. What if your basement is finished and the ducts are mostly behind drywall? Gaps in most ducted systems tend to be located in tight spots where it was tough for the original installer to do any sealing. Typically, small parts of ductwork have to be removed so that a technician can gain access to many of the least accessible locations.

Sealing with Aeroseal

Here's how it works. First, all the intentional openings in the ductwork-supply registers and return-air grilles are blocked off. Then the contractor sets up a number of tools next to your furnace: a computer and printer, sensitive air measurement devices, a blower with a precise fan, and a sealant module with a heater and atomizer. The blower forces air into the ductwork, and devices are used to measure both how much air your ductwork is moving in total as well as the amount being supplied through each register.

Before turning on the aerosol sealant, the contractor locates as many large holes as he can and covers those with mastic or, if large enough, with a piece of sheet metal. After all the large holes spotted have been sealed and the ducts are pressurized with air, a high-tech aerosolized mastic is injected into the ductwork. The sticky vinyl polymer particles remain suspended in the pressurized ducts while slowly migrating toward any air leaks. Where air leaks out, air creates a disturbance which causes the air-borne liquid to turn into a solid; the polymer particles build up around the edges of each leak, slowly drying and sealing off gaps and holes. There's a small odor in the house during the sealing process, but it should dissipate within hours.

Can't seal every home

An estimated 10 percent to 15 percent of homes are missing a piece of sheet metal, half a square foot or larger, from their ductwork system. These larger holes can have major impacts on comfort, energy bills and indoor safety.

Since the Aeroseal method works best on small holes-1/4-inch cracks and smaller-those large holes usually have to be found and covered with sheet metal before the system can effectively do its job. The larger the remaining holes, the longer the installation takes. At some point, if there are still large-sized gaps in the ductwork, contractors may not be able to maintain sufficient pressure to inject the aerosol. In such cases, this sealing system won't work. When these situations arise, Dennis Lubbers (Air Flow Solutions; 303-635-1010) says he does not try to seal the system and the homeowner only pays about $95 for a testing and diagnostic fee.

Costs and benefits

Lubbers reports that sealing a furnace and its ductwork should cost around $400 in a new home, but closer to $800 in an existing home. Why the big difference? First, set-up takes a lot longer in an older home; there's a lot of furniture to move out of the way, etc. Secondly, normally the equipment will have to run twice as long to seal the holes, since many of the larger holes that would be sealed quickly with mastic in a new building are inaccessible in older homes.

Will you get your money's worth? If you have comfort problems caused by leaky ductwork, the Aeroseal system should dramatically reduce those problems. It will also save energy, but typically not enough to justify the investment. That justification will have to come from the comfort improvement. There is also a direct side benefit to the procedure, since before-and-after testing includes a combustion safety test to see if your heating system is causing any carbon monoxide hazard in your home.

Dave Schrock, with Comfort Air Distributing Inc., teaches builders about heating system performance and problems. While very aware that ductwork leaks in virtually all Colorado residences, he was a confirmed skeptic regarding the Aeroseal system. After getting his ducts sealed, Schrock was amazed that the system sealed about 80 percent of the leaks measured at the start of the test; "I couldn't believe it. And the comfort difference from before to after the sealing has been phenomenal." Several other professionals in the building industry have tried the system and are pleased with the results.

So while the Aeroseal system isn't a guaranteed cure, for any homeowner with a serious comfort problem, this approach is worth a very close look. Builders should give the Aeroseal approach a hard look as well, since it should eliminate many common comfort callbacks associated with ductwork.

Steve Andrews consults with builders for E-Star Colorado and writes on energy issues (sbandrews@att.net). E-Star (www.e-star.com), is a nonprofit home energy rating system that works with both new and existing homes statewide.

2008 Built Green Colorado

Home Builders Association of Metro Denver, 9033 E. Easter Place, Suite 200, Centennial, CO 80112
(303) 778-1400 fax: (303) 733-9440  info@builtgreen.org

Last Updated: 10/05/2007