Your home’s HVAC system is what makes it a place of warmth and refuge on a bitterly cold winter day and a welcome abode of relief when it’s sweltering hot outside.

But whether it’s hot or cold outside, research by the Environmental Protection Agency (EPA) shows that most people spend 90% of their time indoors. That means that the air you breathe inside your home takes on an added level of importance.

What keeps your indoor air clean and pure are the filters of your HVAC system.

Don’t Ignore Filter Maintenance

Unfortunately, research also shows that many people are lax when it comes to changing up their HVAC filters. It’s unfortunate because filters scrub your interior space of things like mold spores, dirt/dust, pet dander, tiny hairs, microbes, biological pollutants, insect specks and more. Getting rid of as much of this stuff as possible is important to your health.

Keep in mind that homes today are more tightly sealed than ever before. That’s because of improved insulation materials and better door and window sealing technology. Even a home’s exterior siding plays a role in how well your house can “breathe.” All that is mostly good because it makes your home energy efficient and comfortable. It is problematic, however, for people with specific conditions, such as asthma, COPD, heightened sensitivity to lung allergens or other allergens, pneumonia and others.

Furthermore, HVAC filters protect the investment you have in your heating and cooling hardware. By regularly switching out and maintaining fresh filters, you prevent expensive damage to your furnace, AC units and other devices.

The great news is that keeping your HVAC filter system up to date is easy and not time consuming. In most cases, it involves simply taking out an old filter and slapping in a new one. Usually, no tools are needed and technical skills are not required. Filters in furnaces and air conditioners are made to be “easy-in and easy-out.”

Different Kinds of Filters

Air filters for HVAC units are made in a number of shapes, sizes and configurations. They have different material profiles that determine their capabilities. Let’s review the most commonly used.


Generally the most affordable, flat-panel filters contain fibers most often made from fiberglass. These materials are stretched across a framework. They are a snap to install and usually disposable. They are inexpensive. A small drawback is that they are not as effective as other models in filtering contaminants from the air.


Also disposable, pleated filters are made from screens of dense cotton or plastic fibers. As their name indicates, they are pleated whereas flat-panel filters are not. The pleats create a greater surface area to trap more unwanted debris. They’re slightly more expensive than the flat-panel model.


Electrostatic filters go a step further than ordinary flat-panel and pleated filters because they create a dynamic action without needing movable parts. These filters can create a usable electrostatic charge.

This is accomplished by putting layers of different material together whose natural properties cause electrostatic action to occur between them. The first layer is a blend of tightly woven polyurethane and polypropylene fibers. An outer layer is made of polyester mesh. When air molecules pass through these two substances, it creates natural electrostatic electricity. This is good for making stuff cling to the filter material.

Think of when you rub a toy balloon against your hair or a shag carpet and then make it stick to your forehead! That’s the drawing force of electrostatic charge. It makes these filters good at catching very tiny particles and making them stick to the filter. That includes even microscopic particles like bacteria and smoke granules.

Electrostatic filters can be disposable or washable.


Speaking washable, this quality is treated as a filter variety. Some are sold in both flat-panel and pleated model varieties. Particle build-up in washable filters is handled by simply hosing them down. Because you don’t throw them away, they are more eco-friendly. However, the downside of washable electrostatic filters is that they lessen their ability to charge with every washing. Even so, washable filters save a lot of waste over the disposable filters your throw out after every cycle of use.

HEPA Filter

The HEPA filter has been the “gold standard” for filters for several years. HEPA stands for High-Efficiency Particulate Air. These filters are rated to remove 99.97% of particles in the air — if those particles are of 0.3 microns in size or larger. HEPA filters are used in many different applications beyond HVAC systems. For example, they can be found in some vacuum cleaners and in stand-alone air purifying devices.

HEPA filters are used in industrial settings, such as circuit board fabrication labs, where super clean air is a must. They are also favored by hospitals and laboratories. People with breathing conditions use them to filter the air in their homes.

Because a HEPA filter is extremely dense, not all HVAC systems can handle them and circulate air properly at the same time.

Explaining the Numbers That Rate HVAC Filters

You may have noticed that filters come with a numbered rating between 1 and 16. This is the scale developed by the American Society of Heating, Refrigeration and Air-Conditioning Engineers. It’s called the MERV number.

MERV stands for Minimum Efficiency Reporting Value.

On the 1-to-16 MERV scale, one designates the weakest filter and 16 filters are the strongest. Note that some brands don’t abide by the MERV scale. For example, 3M has its own scale it calls the Microparticle Performance Rating.

Just to let you know and to avoid confusion, there is another often-used filter rating system. It’s the CADR or Clear Air Delivery Rate. It is recognized by the Federal Trade Commission and the EPA. As with MERV, high numbers mean the most efficient and effective. CADR goes from 1 all the way up to 1200. Most filters are rated between the 12 and 240 range on the CADR scale.

It can be highly practical to know how the CADR rating system works when you are seeking to buy an air filtration device for a particular room. For example, you can take a filter’s CADR rating and multiply it by 1.55 to judge the size of a room it will effectively filter.

Thus, if a filter has a CADR of 100, multiply that by 1.55 and you get a room size of 155 square feet.

How Do I Choose an HVAC Filter?

You start with the MERV or CADR numbers we just discussed.

Again, the highest MERV or CADR translates to the most effective filter. A family wherein some members have a high degree or breathing problems, asthma or allergies will want to select with the highest CADR or MERV rating that their HVAV hardware can accommodate.

A warning: You should seek the advice of an HVAC professional if you want to choose a filter with a very high MERV or CADR rating. That’s because some HVAC systems are simply not powerful enough to push air through highly restrictive filters. This has a large effect on how well your home is heated or cooled. You may even damage your hardware.

At the very least, check the user manual that came with your HVAC equipment.

Next comes budget considerations. You’ll find that the disposable filters made of fiberglass are the most affordable upfront. They average about $5. The washable type filter averages about $9 — but, of course, you can reuse it and save in the long run.

Another recommendation is to measure the room space your system will be handling and the size of your ventilation openings. You then multiply the MERV or CADR rating by the dimensions your calculation comes up with. Granted, this step is beyond what many people feel comfortable doing. Don’t feel bad about that. You’re not alone. The good news is that your HVAC professional will be glad to help you with this step.

Finally …

The most important take-away from this article is that everyone should not ignore the regular maintenance of their home’s HVAC filters. The easiest thing to do is replace them on a regular basis, either using disposable filters or the kind you wash out and put back in.

Don’t skip this small but necessary chore. It will help you maintain good health by protecting the purity of air inside your home and by keeping your HVAC system operating at peak efficiency.