Duct leaks are a fairly common way to lose conditioned air
and suck outdoor air into your home (see "Those
Wild Ducts"). I once worked on a new 4,000 square
foot upscale suburban home that smelled like a sewer. The
owners had been living in a downtown hotel for three months
to avoid the smell.
My
testing showed that the ducts that carry air from
the house back to the air conditioner, which was
located under the house, were leaking. These leaks
were creating a negative pressure and sucking
in methane from the drain field of the septic
system. That septic field was more than 40 feet
from the basement!
We sealed the duct leaks and the smell went away. (And we
didn’t use duct tape, which does not effectively seal
ducts. The product to use for sealing ducts is latex, water-based
mastic that meets UL 181 specifications.) No leaks, no suction,
no smell.
In the past the solution to duct leakage was to compensate
by oversizing the system. The contractors didn’t realize
that they were compensating for duct leakage. They just knew
that if they didn’t put in a system larger than the sizing
calculations recommended, they would get callbacks from homeowners
complaining that the system wasn't cooling the house sufficiently.
This is like buying a bigger gas tank to compensate for the
fact that it leaks a fourth of the gas you put in it. It might
work, but it makes no sense, and it is an expensive solution.
These leaks can jack up cooling energy bills by 20% to 40%.
As the suburban homeowner I was working with found out, these
leaks also cause makeup air to flow into your home and can
bring in gases like radon and even pesticides from below the
soil. One interesting experiment showed that depressurized
homes can draw in soil gases from quite a distance. As an
agronomist told me after attending one of my trainings, "People
don’t realize that the air moves through the soil like
wind blows through the trees. If it didn’t, all plant
roots would rot and the plants die."
The house is a system, and that system extends out into your
yard. Outdoors, what you put on your lawn and under the house
for pests and termites can affect the quality of the air you
breathe inside the house. Indoors, how well your air conditioning
and heating system works can affect much more than your energy
bill. Ignoring or not understanding the interactions among
a home's components can lead to some surprising, and often
nasty, home performance problems.
