Nov 19, 2018

How do I know what size air filter I need?

If you’re like most homeowners, you just go to the hardware store and pick whichever filter fits your air duct and your budget. But while this method saves you time in the store, it may not save you money or improve your health in the long run. Ill-fitting, overly restrictive, or inefficient filters can run up your energy bill and produce poor air quality in your home. This guide to air filter types will help you make a wiser selection.

Minimum Efficiency Reporting Value

Every filter has a minimum efficiency reporting value, or MERV rating. This is a measure of the number of particles a filter can trap, compared to the total amount of air it’s trying to filter. Basically, if you put two air filters in the same room, the one that traps more particles has a higher MERV rating than the other. MERV ratings range from 1 to 16. A MERV 16 air filter would be used in a hospital, for example, since it filters out as many particles as possible. A MERV 1 air filter is the least expensive, because it’s the least effective.

So you should always go for the air filter types with the highest rating, right? Actually, a high efficiency air filter can make your HVAC system less efficient. As the filter catches more fine particles, it blocks air flow across your heat exchanger. Your system works harder to heat or cool the air. Your energy bills go up, you need to change the filter more often, and your furnace might become damaged from overheating.

Best Air Filter Types

The best filter for your home is one that removes the most pollutants from the air while allowing your HVAC to perform at peak condition. Older HVAC systems or systems with leaky ducts could perform better when equipped with filters with lower MERV ratings. You may need to experiment a bit to find the best filter. Luckily, most of your choices are relatively budget friendly.


Fiberglass filters are popular because they are inexpensive. They’re often blue; you’ve probably seen them in hardware stores. These thin, flat surfaces are composed of a dense fabric of glass fibers, most of which run perpendicular to the airflow. They tend to have the lowest MERV ratings, often between 1 and 4.

While fiberglass filters do an excellent job of protecting your HVAC unit from large dust particles, they’re not the best filters to use if you have allergies. They will not trap mold, pollen, or other small irritants.


Pleated filters are made up of folded sheets of cotton or polyester-blend fabric. They fold like an accordion, fitting more fabric surface into a smaller area. These filters are often high efficiency; to promote better air flow, look for one with lots of pleats. The more pleats it has, the more easily air can pass through this filter. A pleated polyester filter with a MERV value of 6 to 8 would be an ideal solution. It removes many pollutants from your home without taxing your HVAC system.


Electrostatic filters often have MERV values of 10 or greater, so they’re very effective at decontaminating the air inside a home. They contain multiple layers of polyester-blend materials framed by a polyester mesh. These filters create their own static charge. As air passes through the positively-charged outer material, it transfers the charge to the particulate matter. The charged particulate matter is attracted to the negatively-charged inner material, and sticks to it.

Electrostatic filters trap all kinds of particles, including mold and pollen. Smokers or people with allergies or asthma may find this to be among the most effective air filter types. However, disposable electrostatic filters can be on the pricey side. They may overtax your HVAC system if it can’t handle the limited airflow.


These filters are similar to their disposable brethren, but are usually framed in aluminum, cased in aluminum mesh, and made of washable material. They’re very cost-effective; their average price is around $20, and you only have to replace them every 3-5 years. To maximize their effectiveness, you need to wash these filters every three months or so.

There is some debate as to whether washable filters actually live up to the hype. They can have MERV ratings of 10 or greater, but they aren’t always high efficiency, and it’s sometimes difficult to tell the difference. If they’re not fully dry when you return them to your air exchange, they can grow mold and bacteria that is then circulated throughout your home. They can also bend, warp, or break during washing. If you choose a washable filter, be sure to check its MERV rating, clean it regularly and carefully, and dry it thoroughly.

The Environmental Protection Agency suggests that consumers contact an HVAC technician to determine the most appropriate air filter for their systems. Remember, an air filter serves two purposes: to clean your air, and to protect your HVAC system from damaging particles. Keep both in mind when you’re deciding which air filter to buy. If you need any ac repair or maintenance in Raleigh or Wilmington, contact Newcomb and Company today!

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