Air Filters, Efficiencies
Air filters have a standard rating. This rating, minimum efficiency reporting value (MERV), is a number
from 1-16. You don't have to know all the technical jargon. Simply put, as the number goes up the unit
will stop more and smaller particles.
**NOTE** If you decide to replace your existing air filter with one of a higher MERV
rating, you should check to make sure you have sufficient airflow after you replace it. This is done by
checking the temperature rise in the heating mode and the temperature drop in the cooling mode.
Many hvac units come with a washable type of filter. These will usually be made of foam. These have a
merv rating of 1 to 4.
You can also use a disposable type which is normally made of fiberglass. These have a merv rating of 1 to
Usually you can hold those types of filters up and see through them. If that is the case, you know they
are not doing their job.
Another disposable type is the pleated filter. These have a merv rating of 5 to 8. These products have
more surface area to catch the dirt. They also distribute the airflow more evenly. This means the fan is
less likely to pull the dirt through the filter. This is the type of filter that we recommend for most
applications. They are the best value in terms of price for the filter and keeping your hvac system clean.
Air filters with the higher MERV ratings are sometimes called allergy filters or media air cleaners. They
are typically five inches wide and so have much more surface area to capture airborne contaminants. Before
shopping for these filters, you can check out our brand reviews.
Some are made of advanced materials which set up a static electrical charge. They are called electrostatic
filters and are able to capture much smaller particles.
Some come with an antimicrobial treatment. This prevents organisms from living on the filter when they are
Using the right air filter is only half of the answer though. If it is not replaced often enough, your
hvac system operating efficiency will go down. This will cost you on your utility bills as well as wear
and tear on the hvac unit.
Most people, even those in the hvac industry, don't change their filter as often as they should. It is
usually out of sight and out of mind.
Most hvac service companies offer service contracts where they
change your filter. These contracts can be expensive when you consider you can do it yourself.
There are other options if you have special needs such as allergies. The ultimate filter is called a high
efficiency particle arrestance (HEPA) air filter. They were originally developed during World War II to
stop the escape of radioactive particles from nuclear laboratories. To qualify as a HEPA air cleaner a
unit must meet DOE standards which says that the units must remove 99.97% of particles that have a size of
0.3 microns. They are available as whole house units that can be added to a forced air HVAC system or
portable units. Before you purchase these units, you can check out our brand ratings and shop with
You should also keep in mind that if the filter is a part of the central hvac system and the fan is not
continuously running, then most of the time the filter will not be doing anything.