All ABOUT AIR FILTERS
WHY FILTER THE AIR? :
The average human breathes about 16,000 quarts of air each day. each
quart of air we breathe has about 70,000 visible and invisible
particles. The U.S. Environmental Protection Agency (EPA) notes that
indoor air is often more polluted (five to ten-times more and
occasionally 100-times more) than outdoor air. Today, more than 50
million Americans suffer from allergy and asthma problems caused by
pollen, dust, mold spores, pet dander, mildew and gases that
circulate in the home. Most of the pollen, mold, dust and particles
people breathe into their lungs is approximately three microns or
smaller much less than the size of a human hair.
Good indoor air quality (IAQ) depends on a number of factors,
including effective filtration, which provides the primary defense
for homeowners and HVAC equipment against particular pollutants.
Your heating and air conditioning system is most efficient when the
airflow is at its peak. Simply put, if your A/C coil or ductwork is
clogged, the airflow is diminished. That means the system must run
longer to heat (or cool) the same amount of space. If you filter the
air as it enters the system, your equipment won't get clogged up. If
you neglect the filter long enough, the A/C coil will get so
clogged that the air conditioning evaporator coil will freeze into a
solid block of ice. To repair this will require a service technician
to take the system apart and clean it and a fat wallet.
You take pride in your home. You vacuum, you dust the furniture, you
clean the walls. Now look up at the ceiling! Where did that ugly
black film around the supply air registers come from? In an older
home it can be a sign of dirty air ducts caused by using an
inefficient air filter. No matter what the cause, it is dirt, smoke,
pollen, and dust that was not caught by the filter. You can wash it
off but it will come back.
Air pollutants are; dust, pollen, dust mite remains, mold spores,
animal dander (mold food), smoke, bacteria, and viruses. Of all the
above, Pollen and Mold Spores are constantly being brought in the
home on your clothes and hair. Dust Mite remains, Smoke and Animal
Dander (skin flakes and hair) serve as food for mold and are also
allergens. In general, any airborne organic matter is mold food.
A LITTLE BIT ON THE SUBJECT OF MOLD:
Mold requires three things to survive: appropriate temperatures,
food, and moisture. Mold is a plant that lacks chlorophyll and
therefore cannot produce it's own food. It must trap airborne
organic matter and ingest it. One of the most important components of
control is the limitation of moisture in the environment and in the
HVAC system. Indoor spaces must have a controlled humidity level of
less than 60% for mold free environments.Once mold gets in your HVAC
system it will reproduce at a rate of up to 33 million plants in a
24-hour period. It reproduces by releasing spores into the air.
Mold spores are within the 1 to 10 micron size. That's about one-
fiftieth the width of human hair. These spores are somewhat like
seeds of a plant and will grab a foothold in the system or the
ductwork if allowed to. These spores must be trapped as they pass
by in the air in order to control the mold. A good quality filter
will do just that. And, the more spores captured, the less
probability that mold will grow.
TYPES OF FILTERS:
1. Disposable air filters:
The most common is the standard fiberglass media filter with a
cardboard frame.It looks like blue cotton candy in a box. If you
hold it up to a light you can see right through it. This type of
filter will cost you about $1.99 US if you get it from your local
grocery or hardware store. You just install it in your furnace or
and throw the old filter away. They are not very efficient but they
do offer some protection to keep your air conditioning coil from
getting clogged up. They only remove the large particles of
dust.While better than nothing, they are not a lot better.
The most simple way to demonstrate this is to pour a handful of fine
dirt or pepper on to the filter and watch how much falls through it.
These type of filters will only remove approximately 10 - 15% of the
dust in the air. That means that about 85 - 90% of the dirt, dust,
pollen, and other airborne pollutants will pass through the filter
and either become lodged in the evaporator coil (which over time can
and will cause the air conditioner and furnace to run inefficiently,
increasing electrical and gas consumption ), or put the contaminants
back into the air stream for us to breath. Breathing airborne
pollutants often triggers allergy, asthma, and hayfever
2. Hog Hair
Hog hair filters falls under the category of washable air filters.
They somewhat resemble a flattened bundle of plastic coated thread.
The main ( and only) advantage to them is that they can be washed.
* No more trips to the store to get a new disposable filter.
* They have a life span of two to three years.
* Hog hair filters are pretty inexpensive too. They cost about $5.00
* They are not very efficient.
* Hog hair filters only capture 10 - 15% of the particles in the air.
better than nothing.
3. Wire mesh
If you have an exhaust hood over your cooking range you have probably
seen a wire mesh filter. You probably call it a grease screen. The
heating and air conditioning version is just bigger. It is more
efficient than the hog hair filter (not much though) and they tend
to last a little longer. The wire mesh filter can capture about 15 -
25% of the particles in the air.One problem with them is that the
frame is easy to bend and the media can get snagged on things when
removing it to clean. Once the media has bunched to one area it is
very hard to return it to it's original shape.
Before the advent of Electrostatic Air filters the Electronic air
filters were the best type of filter available to the general public.
They require household current to operate. In general they work as
* 110 Volts AC is stepped up to about 5,000 Volts DC.
* This high voltage is transmitted to electrodes inside the filter
grid as air is forced across it.
* Particles of dust will "short" across the electrodes causing an arc
of electricity that gives the particles a static or positive
* Electrodes further inside the filter are charged with an opposite
or negative static charge.
* In electricity as well as magnetism opposites attract and the
positively charged dust particles are attracted to and stick on the
negatively charged electrodes.
* The filter is periodically cleaned with soap and water to remove
what it has collected.Electronic air cleaners can be quite efficient
(70 - 90%) but they do have a downside.
* First, they are noisy. They sound like a bug zapper and this goes
on as long as the system is running. Many people find this to be
quite annoying. However if the air handler is in the garage it will
not be annoying.
* Second, they tend to loose efficiency as they get older.
* Third, they are a bit expensive to buy and if they break (for
example during cleaning) you must pay to have them repaired (if it is
* And finally, you need a qualified professional to install or
5. Electrostatic Air filter
An electrostatic Air Filter is very efficient. It removes up to 95.3%
of airborne particles.An electrostatic filter uses electrostatically
charged polypropylene and polyurethane filtration medias to attract
particles as small as .3 micron. (1 micron = 1/25,000 in.). A safe
static charge is produced by forcing air across the filter.
This static charge attracts and traps airborne particles into the
filter just like a magnet. Simply clean the electrostatic filter
every 3 - 4 weeks with mild soap and water.
WHAT FILTERS DO:
A "good" filter can remove dust, pollen, dust mite remains (mold food
and an allergen), mold spores, animal dander (mold food), smoke,
bacteria, and some filters even viruses and smells. A "good" filter
is one that has the ability to trap 80% or more of the above
particles. All of these particles are "microns" in size. A micron is
one millionth of a meter or about 1/30,000 of an inch. As an example,
human hair is 70 microns thick. The following table gives you the
size ranges of the above particles:
PARTICLE TYPE SIZE RANGE (microns)
Pollen 10 100
Mold Spores 1 50
Bacteria .5 - 5
Pet Dander (mold food) .1 10
Dust .01 100
Smoke .01 1
Virus .003 - .5>/PRE>
Most filters are rated in MERV. MERV stands for Minimum Efficiency
Reporting Value. A higher MERV indicated better performance.
A MERV 13 filter with six air changes per hour would have an
approximate 100% efficiency in capturing molds.
The higher end
of most "off the shelf" filters is MERV 11. An electrostatic MERV 11
filter will be more than ample to remove 90 95% of the pollutants
with the exception of Smoke, Viruses, and some bacteria (98% of all
bacteria known to man are over 1 micron in size and thus trapped by a
MERV 11 filter). As an Example, 3M Corporation sells the "Filtrete"
electrostatic MERV 11 filter in various sizes within a range of $5
to $9 dollars each (try Home Depot, ACE hardware, or Loews and your
local Supermarket). It is a white accordian-pleated filter. These are
3-month filters so it is well worth the money to insure a clean
WHAT FILTERS DON'T DO:
Filters will do nothing if there is no airflow through the system.
Air must be moved through the filter in order for it to remove mold
spores and other contaminants. It is recommended that the HVAC system
should be able to recycle the house air volume six times in an hour
in order to have peak air cleansing performance.
No matter what kind of filter you get it will be worthless if there
are leaks in the system at any point past the filter (we'll talk
about the resolution in another flyer).
THE WORST FILTER TO HAVE IS PROBABLY THE ONE YOU
Most HVAC systems are installed with a manufacturer's or Low-
efficiency filters. They are typically used to keep lint and large
particles from clogging the heating and cooling coils of an HVAC
system. If you take it out it will have a blue color and be pretty
much see-thru when put up to the Sun. They do nothing for your
indoor air quality (try pouring pepper or salt on them and watch it
drop right through).
PROPER HVAC AIR FLOW:
Your HVAC system should be able to recycle the house air volume six
times in an hour. If your AC Company is reputable, it installed the
proper size system and you don't have to worry. They usually try to
sell you = to 1 ton more than you need so it should be OK. A rough
rule of thumb is to take your home's area in square feet and divide
it by 500. That number should be the number of tons your
HVAC system is rated for plus or minus = ton(or more tons if you have
high ceilings). As an example, a 1,000 square foot home has a volume
of approximately 7,000 cubic feet (7 foot ceilings). Therefore the
system must recycle 42,000 cubic feet per hour (7,000 times 6). A
typical HVAC system is designed to move 400 Cubic Feet per Minute
(CFM) per ton. Each ton of an HVAC system will efficiently cool/heat
400 - 600 feet of your home. So a 1,000 square foot home would have
a minimum of a 2-ton system installed. That's 800 cubic feet per
minute times 60 minutes or 48,000 cubic feet per hour (more than 6
times the volume needed shown above).
WHAT FILTERS TO USE:
You should think of a filter as preventative maintenance equipment.
If you do not have a mold problem initially, the right filter will
prevent any future growth. Good filters will clean the indoor air
and remove a very high percentage of spores but remember that a
filter is not the magic cure all. Other things must be done if
infestation is high (we'll discuss this later). The good news is even
a MERV 6 pleated filter will remove 80% of the mold spores passing
PROPER REPLACEMENT TIMES:
Most manufactures will tell you when to replace the filter (i.e.
every month, 3 months, etc.). It is absolutely necessary that you do
so. You must remember that all manufacturers recommended replacement
times are based on perfect indoor conditions. If you have pets,
smoke, or burn candles a lot the replacement time should be
approximately half the manufacturer recommended. Dirty air filters
themselves can provide a breeding ground for mold and mildew. A
clogged filter will slow down the airflow to the system and can
create expensive problems in your HVAC system if left dirty. On the
contrary, the efficiency of filters generally increases as they trap
particles (a three month filter is most efficient at approximately 2
months then when first installed).
HELPFUL HINTS TO REDUCE POLLEN AND MOLD IN YOUR HOME:
Keep the HVAC fan on 24 hrs. in the spring and fall to keep air
moving to remove mold spores. These seasons are the periods noted for
high pollen and spore counts.
SHOULD YOU CLEAN YOUR SYSTEM?:
IF I FOLLOW THESE HINTS WHAT WILL I SAVE? :
My business (The Environmental Air Force) is prosperous because I
clean ducts and remediate mold. It has been my experience that the
majority of homeowners needing duct cleaning needed it because
they either had manufacturer's filters or didn't change the filters.
In addition, I work with AC Contractors daily and the number one
reason systems fail to operate properly is due to excessively dirty
filters. By maintaining clean, efficient filters you won't need two
or more service calls a year and you won't need a duct cleaning,
Mold remediation, and Air Handler cleaning. The average "no air"
service call runs between $125 and $200. The average Duct Cleaning
Service costs $400-$700. The average mold remediation and
microboicide treatments cost $175. The average Air Handler Cleaning
(blower pull and clean, evaporator coil clean, and condensate pan and
drain clean will cost $500. So you will probably save between $1,325
and $1,775 just by keeping the system clean. Plus the added feature
of clean, mold, pollen, dust mite free air. I hope that makes you