Leaks in a home's supply ducts cause uneven air delivery and blow heated
or cooled air into attics or crawl spaces, where it is lost to the outside.
Leaks in a return duct pull in outside air, so the system has to work
extra hard; return leaks can suck in chemical fumes, exhaust, or other
The best way to seal most leaks is with an aerosol system developed by
Berkeley Lab's Indoor Environment
Department. After registers are sealed so that air can escape only
through leaks, microscopic polymer particles are injected into the ducts.
These stay airborne until forced to exit at a leak.
"It's like driving your car fast, which is fine on the freeway,
but if you turn too sharply you skid out," Modera explains. "The
air flow has to turn a sharp corner at a leak, and the particles skid
out and smash against the edges."
infrared image, courtesy of Sierra
Pacific, reveals hot air leaking from the attic.
The sealant builds up and closes leaks in ducts made of metal, plastic,
or any other material, sealing all gaps up to a quarter inch wide within
15 minutes. Ducts sealed this way show no leakage after four years of
high pressures and constantly cycling temperatures. Under the same conditions,
duct tape typically fails within three days!
Modera founded Aeroseal, Inc., to commercialize the technology. The Aeroseal
company supplies equipment including laptop computers to run diagnostic
and monitoring programs and trains and licenses contractors across
the country. If a duct system needs sealing, the cost can be recouped
in energy savings in one to three years.
The technology was named one of Popular Science magazine's "Best
of What's New," consumers voted it one of the best products to come
out of the Department of Energy, and a panel of experts chose it as one
of the 100 best innovations in DOE's first quarter century.
- More about Aeroseal, Inc., and
aerosol-based duct sealing
off Commercial Waste
Commercial buildings use over a third of the electricity and
almost a fifth of the natural gas consumed in California. In commercial
buildings, more people use more lighting and equipment; space
for space, energy waste in commercial buildings can be double
that of residences.
Berkeley Lab researchers have studied energy loss in the ventilating
systems of light commercial buildings such as shops and libraries
and in large commercial buildings like office towers as well.
Light commercial buildings are typically only one or two stories
high and use the same materials and construction techniques as
homes. Their heating, ventilation, and air conditioning (HVAC)
systems are rarely custom designed; instead an HVAC "package"
is installed on the roof which usually consumes more power
than is needed.
Ducts are usually inside, but many of them run through ceiling
spaces where leakage causes the same kind of loss as home attics.
In large commercial buildings, leaks lead to huge increases in
the electricity needed to power fans and blowers.
In addition to using the right size of HVAC unit, and heating
or cooling only the needed volume of air, the best way to save
energy in commercial buildings is to fix leaking ducts. Aerosol
sealant is the most effective, but duct systems in commercial
buildings are more extensive and more complicated than in the
typical home and need special techniques. Rather than one big
injector for the whole system, for example, a compact particle
injector used for various segments works better in large commercial
- More about
heating and cooling commercial buildings
about Mark Modera and his aerosol sealing system