Different kinds of Gas Furnace Filters
Gas furnace filters come in a variety of qualities and materials, and they differ in thickness and lifespan. Some are reusable and require washing, while others need thrown in the trash after a single month. Knowing which furnace filter to choose requires you understand the different types of filters and the terms associated with them. It also requires that you understand your needs and preferences, as no one air filter works for all applications.
Gas Furnace Filter Terms
Knowing which gas furnace filter to choose begins with understanding three common terms: efficiency, electrostatic, and activated carbon.
Gas furnace filters were originally developed to protect furnaces from dust and other large, airborne particles. While this is still their primary function, filters today also play an important role in improving air quality.
Despite some disagreement, studies have shown filtering air through an HVAC system does improve air quality. In fact, furnace filters are better at removing allergens and reducing symptoms in people with asthma that single-room filtration units. Home and business owners have to change or clean their air filters, however, for them to help air quality.
It is also important to note that filters only remove particles from the air when the HVAC system is running. So, if the temperatures are moderate and the AC or furnace is not on, you will have to run the fan to circulate air for the filter to have any effect.
How well filters perform at removing particles from the air is measured with a minimum efficiency rating value (MERV). MERV ratings range between 1 and 20, where MERV 1 filter only scrub out the largest particles from the air and MERV 20 filters scrub particles as small as viruses from the air.
As a note, 3M, one of the most popular gas furnace filter brands, uses its own rating, called microparticle performance rating (MPR), to describe its filters efficiency. Several sources have set 3M’s ratings side-by-side with industry-standard MERV ratings, so it is possible to compare them.
The positive thing about higher-rated filters is that they remove finer particles from the air. In medical and hazardous settings, this can literally save lives. It can also help reduce allergens in homes and ease symptoms of asthma.
These higher-rated filters have a downside, however. They offer more resistance to air passing through them, which makes the HVAC system fans work harder to move air. Depending on the fan’s motor, this extra resistance can add between a small to a significant increase in energy usage.
For more information about how gas furnace filters affect air flow, check out this research article from Home Energy.
Another downside to more efficient filters is that they can interfere with a furnace’s performance. If not enough air flows over the heat exchanger, the furnace can overheat, which can damage it. To little air can also affect the furnace’s air-to-fuel ratio, which will affect the unit’s efficiency.
When you begin researching air filters, the terms electrostatic and nonelectrostatic will come up often. Electrostatic does not so much a type of filter as it describes something the filter does. Electrostatic refers to the phenomenon of static electricity, in which an object builds up an electric charge, which it can then discharge. If you have ever rubbed your socks on the carpet and shocked someone, you have experienced this phenomenon.
Static electricity is produced in gas furnace filters as air passes through the filter’s fibers. No plug-in electricity is required. The charged fibers (or strands) in turn attract particles in the air, and the particles stick to the filter.
Electrostatic filters range in efficiency from 2 to 10 MERV, and they come in disposable and nondisposable forms. The best quality disposable ones can last years. Nondisposable electrostatic furnace filters need washed.
The Term “activated carbon” also does not describe a type of filter. Instead, it describes something applied to a filter. Activated carbon is primarily used to help filters reduce vapors and odors. It is sprayed onto a filter and does not affect a filter’s MERV rating.
Types of Air Filters
Outside the above terms, gas furnace filters fall into one of five categories: washable, spun fiberglass, pleated, HEPA, and whole-house.
Washable gas furnace filters are typically made with weaved/pleated aluminum, although some are made of synthetic fiber. They come with plastic or aluminum frames, so they are rust-proof, and they typically have electrostatic properties. Unlike pleated or fiberglass filters, they are not meant to be tossed out after they collect dust and other particles.
Washable gas furnace filters do cost more than disposable types. The cost varies significantly, between $20 and more than $100, but they typically last between 5 and 10 years. Some high-quality washable filters have lifetime warranties.
As for their efficiency, their ratings do not go as high as pleated or HEPA filters. Washable filters are available with MERV ratings between 1 and 9.
The positives of these filters are that they are environmentally friendly and that they save money over their life period. Drawbacks to these filters include that they cost more upfront and that they require more work. Owners must spend time rinsing them out. If not rinsed out, washable filters may develop bacteria and fungus.
Spun Fiberglass Furnace Filters
Fiberglass furnace filters are, as their name suggests, made of spun fiberglass. These low-end filters are best at catching large particles such as dust, lint, and bugs. They cost ½ to ¾ as much as pleated air filters, but they only have a MERV rating between 1 and 4. They also have shorter lifecycles than pleated filters because of their low quality (most do not have metal reinforcement). Many fiberglass filters need replaced every 30 days.
Fiberglass filters are best for applications where owners require a filter that provides the minimum protection required for their gas furnace and where air quality is not an issue.
Pleated (Synthetic Panel Filter) and Microfine Fiberglass
Pleated gas furnace filters (also called synthetic panel filters) and microfine fiberglass furnace filters improve air quality better than spun fiberglass filters. Made of spun synthetic fibers, these filters range between 5 and 13 MERV and come in thicknesses between 1” and 5”. Most are nonelectrostatic and offer filtration levels that collect just dust and lint to particles as small as bacteria.
Although these filters are more expensive than fiberglass, they last longer because they are reinforced with metal and better-quality cardboard. For this reason, they need only be changed every 90 days to one year, according to manufacturer instructions.
As a note, if you are just turning on your gas furnace or AC for the first time in the season, or if there are large amounts of dust/pollen/etc. in the air, we recommend checking the filter after 30 days and replacing it if needed.
High-Efficiency Particulate Air (HEPA) filters are a specific type of filter that meet standards set by United States Department of Energy. Originally developed by nuclear industry to clean up radioactive particles, HEPA filters are made of a mat of randomly arranged fibers, usually fiberglass, and are required to remove up to 99.97 percent of particles in the air. HEPA filters will rid air of particles down to .3 micrometers, which is efficient enough to catch viruses.
HEPA filters should only be matched with systems made to work with HEPA, as these filters drastically restrict airflow.
Whole-House Air Filtration Systems
Air filtration systems, such as American Standard AccuClean™, have patented air filtration technologies that make them more efficient even than many HEPA filters. These systems use electricity and multiple filter layers to catch 99.98 percent of particles from, particles down to .1 micron in size. The first layer in the AccuClean™ system is a reusable “pre-filter,” which owners can clean with a vacuum. The second layer charges the air with electricity, making the air electrostatic instead of the fibers in the filter. The third layer captures airborne particles with reusable collection cells. Owners can vacuum this layer, too. This layer requires cleaning only every six to nine months, according to American Standard.
If you are concerned with pollution, whole-house air filtration systems are excellent choices, as they drastically improve air quality when the HVAC system is running.
If you are interested in a whole-house air filtration system, you will not be able to find one in a store. They are sold through select dealers and through American Standard directly. Also, they require that your home’s HVAC system be modified. You will therefore need a licensed HVAC technician to install one of these units.