This article was originally published in the January/February 1998 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online January/February 1998


Not Your Daddy's Duct Sealing Method

By Gary Heederik


An Aeroseal in action: sealant is blowing through the lay-flat tubing into the duct work. 
Gary Heederik first tests for CO in the house before beginning the duct sealing process.
The end of the lay-flat tubing must be sealed onto the end of the duct--the sealant blows from the Aersoseal through this tubing and into the ducts. Duct tape makes an adequate temporary seal.
The Aeroseal controls monitor the system and generate a before-and-after leakage report. 
In new homes and older homes, significant amounts of energy can be saved simply by paying close attention to how a duct system is installed and what materials are used in the installation. Research from Pacific Gas and Electric Company (PG&E) shows that the average new home has duct losses of up to 400 cubic feet per minute of air loss at 50 Pascals of pressure (CFM50).

In the past, I, like many others, have diagnosed duct leakage with a Minneapolis Duct Blaster. The Duct Blaster pressurizes the heating and air conditioning duct system. Using a hand-held digital manometer, I can very accurately measure air loss in a duct system. Once I've done this, the next step is to reduce that air loss.

Using traditional duct sealing, leaks might go unsealed because they are small and hard to find, or because the duct run is inaccessible. With the use of a new technology that has just recently come to California, that hard-to-find leakage is easier to reach and repair in a cost-effective fashion.

This new technology--called Aeroseal-- is finally available to duct-sealing specialists. Once the duct runs are pressurized, Aeroseal blows in a sealant made up of polymers suspended in a water base. As the sealant crosses a warm air stream before entering the duct system, the warm air partially evaporates the water, allowing the polymers to collect and stick to leaks, attracted to the holes by the low pressure outside the duct system. Once the leaks are all sealed, the change in pressure notifies the Aeroseal equipment that the job is done, and the equipment shuts down.

In September, 1997, Aeroseal Incorporated approached my company, Consumer Energy Management Consulting Incorporated (CEMCO), to participate in a 60-day pilot program to test the Aeroseal product on older homes. I found this product works great on those homes as a cost-effective way to reduce duct losses and consumer energy bills. In general, the technology works well for sealing small leaks, but larger leaks still need to be sealed by hand.

At CEMCO, we have performed diagnostic testing services and repairs for the past several years and have worked on hundreds of homes. With the use of this product, we are able to seal ducts tighter at no additional cost. We can also further reduce leakage in a system that is already considered tight. Our target leakage rate after sealing a retrofit home with the Aeroseal product is approximately 25 CFM25. For a new production home builder this product offers tremendous value in assuring quality control, minimizing consumer energy bills, and reducing the risk of defect litigation issues arising from poorly installed ductwork.

New Home Sealing The process is fairly simple for new homes. The sealing takes place when the ductwork is completely installed but the heating and cooling equipment is not yet set. First I perform a pretest to identify the leakage. Then I follow the same steps as for sealing an older home. Retrofit Home Sealing The process for sealing a retrofit home is a little more complex. I first do a preinspection on the home to make sure it is feasible to seal with Aeroseal. I look for such things as the type of duct work, indoor air quality, and any carbon monoxide (CO) problems. I check any gas appliance for high CO levels and positive flue gas drafts. For obvious safety reasons, if there are problems with air quality or appliance operation, I do not want to proceed further until these problems have been addressed. Once I have determined that it's safe to go ahead, I take the following steps:

  • Hook the Aeroseal equipment to the duct system--either by connecting directly to the system or by cutting into the plenum. To connect directly, disconnect the supply run at the furnace area and connect lay flat tubing directly to the supply duct work (see below). To cut into the plenum, scribe a hole the size of the collar connection of the Aeroseal equipment. Isolate the cooling coil or heat exchanger by blocking it off with duct board or other material. (You don't want the sealant material to get into the coil or the furnace area.) Then screw down the collar with self-tapping screws and seal around the collar with duct tape.
  • Cut off a length of lay flat tubing. This can be found at most hardware stores--it is simply a round plastic bag that comes in a long roll. Clamp one end of the bag to the collar on the plenum and the other end to the Aeroseal equipment. If you are accessing the duct directly, tape the bag right onto the end of the duct to seal off air.
  • Next, tape off the supply registers and run a pressure pretest of the duct leakage, using the preset run test button on the Aeroseal equipment. This establishes the duct leakage in the system before the introduction of the sealant. If the pretest indicates large leaks, crawl the length of the supply runs looking for those leaks. You can find them by feeling for breezes coming out of the duct runs or by hearing air passing through the holes. Seal those leaks by hand before you start the Aeroseal process.
  • After the pretest is done, remove the tape from the registers and cut duct board or blue board insulation to the size of the register. Seal around the edges of the board with duct tape so the register is completely closed off. During the Aeroseal process, you need to monitor these plugs continuously to make sure they're not coming loose. If a pressure difference occurs, indicating a blown plug, the Aeroseal equipment senses it and automatically shuts down the injector unit, preventing the home from being filled with sealant. You must then check all plugs and reseal any loose ones.
  • Install a fan in a window or hook up a blower door unit to pressurize the house. The volume of pressure doesn't seem to matter as long as it is positive. The positive pressure will further help to keep the Aeroseal product from entering the home.
  • Manually seal the return duct runs (the short, straight return ducts are much easier to seal by hand than the supply runs). If a return duct is easily accessible, use a Y connection to join both the supply duct and the return duct to the Aeroseal equipment. This eliminates the need to hand seal the return run.
  • Begin the injection process. This will take from one to one and a half hours; depending on the severity of the leak. When the sealing process is completed, the machine prints a before-and-after report showing the final results of the sealing.
Along with leakage, other items should be checked to improve comfort and efficiency levels, like properly sized heating and air conditioning equipment, a properly designed supply and return system, and duct insulation R-values appropriate to the local climate.

The cost of sealing an existing duct system with Aeroseal is between $450 and $600, depending on what needs to be done, roughly the same as the cost of hand-sealing though less labor intensive. When sealing new homes, this product can be rolled into a total package of improvements provided to the builder, perhaps to qualify for the Environmental Protection Agency Energy Star Home Program (see New Software Helps Sell Energy-Efficient Homes, p. 7) or with the use of the Energy Efficient Mortgage Program (EEM).

Gary Heederik is the senior vice president of Consumer Energy Management Consulting Incorporated in Northern California.


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