Tuning up the distribution side of a forced-air system starts with the blower.
The axle should be lubricated; blades cleaned and lower motor checked to insure
the unit isn't being overloaded. The fan belt should be adjusted so it deflects
no more than an inch when pressed. Every accessible joint in the ductwork should
be sealed with mastic or UL-approved duct tapes. Any ducts that run outside
the heated space should be insulated.
Thermostats can degrade over time as mechanical parts stick or lose their calibration.
Older units will send faulty signals if they've been knocked out of level
or have dirty switches. To recalibrate an older unit, use a wrench to adjust
the nut on the back of the mercury switch until it turns the system on and,
using a room thermometer, set it to the correct temperature. Modern electronic
thermostats, sealed at the factory to keep out dust and grime, rarely need
adjusting. However, whether your thermostat is old or young, the hole where
the thermostat wire comes through the wall needs to be caulked or a draft
could trick it into thinking the room is warmer or colder than it really
Most houses with forced-air furnaces have a standard furnace filter made from
loosely woven spun-glass fibers designed to keep it and its ductwork clean.
Unfortunately, they don't improve indoor air quality. That takes a media filter,
which sits in between the main return duct and the blower cabinet. Made of
a deeply pleated, paper-like material, media filters are at least seven times
better than a standard filter at removing dust and other particles. An upgrade
to a pleated media filter will cleanse the air of everything from insecticide
dust to flu viruses.
Compressed, media filters are usually no wider than six inches, but the pleated
material can cover up to 75 square feet when stretched out. This increased
area of filtration accounts for the filter's long life, which can exceed two
years. The only drawback to a media filter is its tight weave, which can restrict
a furnace's ability to blow air through the house. To insure a steady, strong
airflow through the house, choose a filter that matches your blower's capacity.
Inside the walls and floors of 80 percent of American homes run a maze of heating
and air conditioning ducts that connect each room to the furnace. As the supply
ducts blow air into the rooms, return ducts inhale airborne dust and suck it
back into the blower. Add moisture to this mixture and you've got a breeding
ground for allergy-inducing molds, mites and bacteria. Many filters commonly
used today can't keep dust and debris from streaming into the air and over
time sizable accumulations can form dust bunnies, but bigger.
To find out if your ducts need cleaning, pull off some supply and return registers
and take a look. If a new furnace or air handler is being installed, you should
probably invest in a duct cleaning at the same time, because chances are the
new blower will be more powerful than the old one and will stir up a lot of
Professional duct cleaning includes such benefits as cleaner indoor air, longer
equipment life and lower energy costs. Clean HVAC systems can also perform
more efficiently, which may decrease energy costs, and last longer, reducing
the need for costly replacement or repairs. Cleaning has little effect on air
quality, primarily because most indoor dust drifts in from the outdoors. But
it does get rid of the stuff that mold and bacteria grow on, and that means
less of it gets airborne, which can be a relief to allergy sufferers.