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Filters capture tiny particles of dust, dirt and other debris. This helps improve the air quality in your home while your furnace or air conditioner is in use, but that’s not the primary purpose of a filter. Filters are actually designed to protect your heating or cooling unit from damage. Debris can clog your HVAC system, causing it to freeze, break or run slowly.
The wrong filter can cause irreversible damage to your heating or cooling system. That’s why it’s important to select a filter that protects your unit without drastically restricting airflow. Many people are torn between HEPA filters and HVAC filters, which are also known as furnace filters, AC filters or MERV filters.
WHAT ARE HEPA FILTERS?
HEPA filters, also referred to as high-efficiency particulate air filters, capture tiny airborne particles as small as least 0.3 micrometers. These filters capture at least 99.7 percent of airborne particles of this size, and some HEPA filters grab as much as 99.999 percent of these particles. A filter cannot be classified as a HEPA filter unless it meets filtration requirements established by the United States Department of Energy.
A HEPA filter used in an HVAC system is an HVAC filter. However, not all HVAC filters are HEPA filters.
WHAT ARE HVAC FILTERS?
HVAC filters are filters used in heating and cooling systems. They are also called air conditioner filters, furnace filters or MERV filters. MERV stands for Minimum Efficiency Reporting Value, and it’s used to rate a filter’s ability to capture particles. MERV values range from 1 to 20. A high MERV rating means that an HVAC filter effectively captures a large percentage of fine airborne particles, though not necessarily as well as a HEPA filter.
HOW DO HEPA FILTERS WORK?
HEPA filters generally capture airborne particles via interception or impaction, but diffusion is an option if the first two mechanisms fail. Interception and impaction block the passage of medium and large particles, while diffusion is best for fine particles.
When you purchase a HEPA filter, you may notice it has accordion-style folds rather than a flat design or subtle weaving. These accordion-like folds are made from tightly woven fibers that prevent particles from passing through to your appliance or automobile.
HOW DO HVAC FILTERS WORK?
HVAC filters have porous membranes made from fiber or polyester that promote airflow while capturing appliance-damaging particles. Like HEPA filters, some HVAC filters have pleated designs that capture particles. However, this does not mean that these HVAC filters are authentic HEPA filters.
There are four main types of HVAC filters: HEPA filters, flat-panel fiberglass filters, pleated media filters and washable filters. HEPA filters and pleated media filters generally have the highest MERV ratings, but they often cost more than flat-panel fiberglass filters and washable filters.
It makes sense to choose a HEPA filter or pleated media filter if you have allergies or a respiratory condition. However, there are some drawbacks to using one of these filter types instead of a flat-panel fiberglass filter or a washable HVAC filter. All filters help capture particles and improve air quality, but some of them make it difficult for air to flow through your HVAC system.
For example, HEPA filters block a large percentage of airborne particles, but they also restrict airflow. This may cause your unit to run slowly, overheat, freeze or even completely stop working. The same is true for pleated media filters.
Flat-panel fiberglass filters and washable HVAC filters capture fewer airborne particles than accordion-style filters, but they also block less air. This means your HVAC system is less likely to malfunction, though your indoor air may not be as pure.
As discussed earlier, MERV ratings evaluate how well an HVAC filter blocks particles from entering a heating or cooling unit. MERV ratings range from 1 to 20, with one being the least effective and 20 being the most effective. HEPA filters typically rank somewhere between 16 and 20 on the MERV scale, while fiberglass filters and washable filters rank as low as 1 to 4 on the scale.
HEPA filters are also classified by an alphabetical system ranging from A to F. Filters classified as C, D or F generally capture more particles than filters classified as A, B or E.
MERV ratings don’t just focus on how well a filter blocks particles, though. MERV filters also measure how much an air filter resists airflow and how long an air filter is expected to last.
Permanent HVAC filters exist, though filters generally aren’t designed to last forever. Over time, even washable filters should get replaced if you want your HVAC system to function properly.
Recommendations for filter maintenance vary widely across the internet, so it’s best to follow the guidelines printed on your filter. If you don’t see any, you can contact the manufacturer and ask how often you should clean or replace your filter.
With that being said, you can typically expect to get anywhere from 1 month to 5 years out of your HVAC filters. The exact duration depends on a combination of factors, including:
- The quality of your indoor air
- Whether you have pets
- How well you maintain your filter
- The type of filter you use
- How often you run your HVAC unit
If you have several pets and run your HVAC system often, you may need to replace your filter more often than someone in a pet-free home who rarely uses the air conditioner or heater.
HVAC filters are generally not something you install once and leave in place forever, regardless of whether you choose a high-MERV filter or a budget-friendly model. Depending on the type of filter you use, you may need to care for it by doing the following:
- Vacuuming it
- Shaking off excess debris
- Wiping it down
- Washing it
- Replacing it on a set schedule
Be careful with washable filters. They are prone to mold growth, especially if you don’t let them dry fully before you reinstall them. A damp filter may distribute mold particles throughout your entire home and make you and your family sick.
MERV rating often affects the cost of your filter. A higher MERV rating typically means a higher price, both for the filter itself and your utility bills.
Fiberglass filters and washable filters are generally cheaper than pleated filters and HEPA filters. They also reduce utility expenses because they promote airflow more than tightly woven filters, so your HVAC unit doesn’t have to work as hard.
You should also consider how often you have to change your filter. The cost of a filter that requires frequent replacements, such as once every month or two, can add up quickly.
WHICH FILTER SHOULD YOU CHOOSE?
Consider your health and budget when you shop for HVAC filters. HEPA filters generally cost more than other types of HVAC filters, but they help protect your respiratory system. However, this may not be a priority for you if you have strong lungs or lack a sensitivity to common household allergens.
Washable HVAC filters are inexpensive, but caring for them requires more effort than other filter types. You may find it easier to buy a filter you can discard rather than clean.
Before you select a new HVAC filter, review several different options online or at your local store. This makes it easier for you to select the best HVAC filter for your home or office. And remember, you aren’t stuck with a filter. If you try one and don’t like it, experiment with a different type and see if you get better results.