Q --I run my furnace blower continuously so that the central-air cleaner
is more effective. Does it make sense to use room air cleaners in addition to
the central one or does that just waste electricity?—Ann R.
are now running their furnace blowers continuously for better indoor air quality.
Most blower motors, unless you have a new variable-speed air handler, use a
considerable amount of electricity when you run them continuously. The newer
variable-speed blowers use about two-thirds less electricity.
In most cases, depending on the type of particles (allergens) that you are trying
to remove from the indoor air, running several small room air cleaners can be
more effective. You will probably want to use different types of room air cleaners
for different rooms and air-quality problems. They will probably use a lot less
electricity overall than running the blower continuously.
In addition to indoor air quality, a primary purpose of any central-air cleaner/filter
is to keep the furnace/heat pump heat-exchanger surfaces and coils clean. If
they get dirty, their ability to transfer heat is reduced. This results in lower
efficiency and higher electric bills. They also require care because, as they
become dirty, they increase the resistance to airflow through the furnace or
Good quality central-air cleaners are most effective for removing tiny particles,
like smoke, that tend to stay airborne. Most common allergens, like pollen,
dust mite feces, mold spores, etc., are larger particles. After you walk on
the carpet or plop down on a sofa creating a cloud of them, these larger particles
settle back down before they enter the return registers. For removal of these
larger particles, individual room air cleaners can be very effective.
The two most effective room air cleaners are true HEPA (high-efficiency particulate
air) and electrostatic (electronic) designs.
I have just installed an efficient electronic central-air cleaner in my own
heat pump. I also use HEPA room air cleaners in my bedroom and home office where
it gets dusty, and an electronic model in my family room by the wood-burning
fireplace to take care of smoke.
A HEPA air cleaner works by forcing the room air through a very dense filter
media. HEPA filters were originally designed for use in hospital operating rooms.
To be a true HEPA, it must remove 99.97% of all particles down to .3 microns
in size. This includes almost all allergen particle sizes. When selecting one,
watch for terms on the packaging such as "HEPA-like," which may not
be as effective as a true HEPA.
With the very dense filter media, HEPA air cleaners require fairly powerful
blower motors (100 to 150 watts of electricity) to force the air through the
filter. This consumes more electricity than electronic models. If you also want
to remove odors, select one of the HEPA air cleaners with a large carbon element.
The more powerful motor allows a heavier carbon filter to be used. The replaceable
HEPA filter elements usually last from one to three years.
It is wise to select a model with several fan speeds (three or more), especially
if you plan to use it in a bedroom at night. Ones with large carbon after-filters
will remove some volatile chemicals in addition to odors.
When selecting a room air cleaner, look at
the CADR (clean air delivery rating), a good reference to compare the effectiveness
of various models.