What Materials Are Furnace Filters Made From?
Furnace filters come in a wide range of sizes and shapes from a diverse array of manufacturers, but those are certainly not the only differences to consider. The materials used in the construction of furnace filters have a direct impact on the performance of those filters, including how long they last and the size of the airborne particles they are capable of filtering out of the air in your home.
You depend on your furnace and air conditioner to keep your home comfortable all year long, however your HVAC system does more than just control the temperature and humidity. It’s also responsible for keeping the air in your living spaces clean and fresh by filtering out airborne particles such as dust, pollen, pet dander, and other common allergens. Over time, your furnace filter will build-up these trapped particles as it filters the air, and you’ll need to replace the filter with a fresh one to maintain good air quality in your home and keep your furnace operating efficiently.
When the time comes to replace your furnace filter, there are many factors to consider to ensure you get the right one. For starters, you need to double check the proper sizing of the filter to buy one that fits properly in your furnace. This is fairly easy if you know where to look. Most filters have the sizes printed right on the frame of the filter, or you can check the furnace owner’s manual for the proper specification. For complete details on how to find the right filter size, we recommend you check out our comprehensive Furnace Filter Sizing Guide.
In addition to the size, you’ll also want to consider the filtration effectiveness of the replacement furnace filter so you get one that provides the best level of airborne particle control and energy efficiency. Filtration effectiveness is measured according to the MERV (Minimum Efficiency Reporting Value) scale. The higher the MERV rating, the more efficient the filter is at capturing very tiny airborne particles like dust, pollen, mold spores, and many other particles and allergens. Most home furnace filters start at a MERV rating of 8, and can go as high as 16 in some cases. To get the full story on MERV ratings and what you should buy, head on over to our Guide to Furnace Filter MERV Ratings.
One last piece of the equation that should be considered when shopping for replacement furnace filters is what materials are used in the manufacture and construction of the filters themselves. The materials used have a direct correlation to the durability, capture efficiency, and airflow characteristics of the filter, and can definitely affect the value you get out of a filter when you buy it. Let’s explore the various materials that are most commonly used in the manufacture of furnace filters, and what the differences are between them.
Common Furnace Filter Materials
Fiberglass Furnace Filters – Fiberglass is a very common and affordable material used in the manufacture of air filters for a wide range of applications, including in home furnaces. Thin fiberglass strands are spun together in sheets and surrounded by a paper frame, sometimes with metal reinforcements to add structural rigidity to the furnace filter. Fiberglass filters are generally the lowest cost replacement furnace filters, and only offer very basic particle capture efficiency when compared to other materials. In general, fiberglass filters have a MERV rating of around 4, and will capture larger particles like lint and household dust fairly well, but are typically not as capable at capturing high amounts of tiny particles between 10 and 3 microns in size.
Polyester Furnace Filters – Polyester fibers can be woven together in a much tighter manner than spun fiberglass, allowing this material to provide a greater level of air filtration efficiency. Furnace filters made with polyester are a little more costly than those made with fiberglass, but offer improved capture of tiny particles, airborne pollutants, and common allergens including mold spores, pollen, and pet dander. The MERV rating on polyester filters can range from 6 to 14, depending on the physical design of the filter and its overall depth, making this material ideal for allergy-control filters and other types of higher-performance applications.
Cotton Fabric Furnace Filters – Much like polyester, cotton fibers can be woven tightly together to produce a material with superior particle capture efficiency. In fact, cotton fabric and polyester are more or less equal in terms of their ability to filter out tiny particles in a home HVAC system. This isn’t to say that every cotton fabric filter will work the same as every polyester fabric filter, but if the filter sizes and MERV ratings are equal, then the materials themselves will perform at very similar levels. Some filters are even made from cotton-polyester blends, resulting in virtually no discernable difference in the performance of these two materials.
Electrostatic Furnace Filters – While most furnace filters work by physically trapping and containing airborne particles in between tightly-woven fibers, electrostatic filters use the scientific properties of static electricity to attract and hold particles. Electrostatic filters are often made from metal mesh in combination with special blends of polyurethane and polypropylene. The layers of the filter are both positively and negatively charged, allowing particles of either charge type to be captured as they move through the filter. With MERV ratings ranging from 5 to 10, electrostatic filters can be a good option for some home HVAC applications.
Electrostatic furnace filters also come in washable models that can be removed from the furnace, cleaned, and put back in place. This means the usable life of the filter is quite long, however this also means that they are much more expensive than disposable filters. Depending on how much maintenance the homeowner is willing to perform, electrostatic filters can end up being quite affordable in the long run.
Activated Carbon Furnace Filters – For odour control from sources like smoke, gases, or VOCs (volatile organic compounds), some furnace filters are made with a combination of materials that includes activated carbon. As air containing these compounds passes through the filter, they stick to the carbon and become trapped in the filter, removing them from the air and leaving your living spaces cleaner and fresher. Activated carbon filters tend to be more on the expensive side, but the advantage they provide in controlling unpleasant smells in a home can make them well worth the little bit of extra cost.
What About the Physical Design of Furnace Filters?
While the materials used in the construction of a furnace filter certainly influence how well they work to clean the air in your home, using the same material in different designs can also provide different results. Some filters appear as flat sheets of woven fibers contained in a metal, plastic, or rigid paper frame, while others have a ridged appearance that makes them look more like an accordion. Does this really matter when it comes to how well they filter out particles from the air?
Flat Furnace Filters vs. Pleated Furnace Filters
The reason some furnace filters have ridges or ‘pleats’ in them is to significantly increase the total surface area that the air moving through the filter will come into contact with. You see, as air passes through a filter and airborne particles become trapped, the filter will gradually become ‘loaded’. This means that the accumulation of trapped particles increases over time, thereby reducing the filters useful life and increasing air resistance. Eventually, the filter becomes loaded to maximum capacity and must be replaced.
The holding capacity of a filter is related to the total surface area, as well as the materials used. For example, a flat fiberglass filter will not be able to hold as much as a flat cotton or polyester filter because the materials are different. However a flat cotton fabric filter will not be able to hold as much as a pleated cotton filter because the surface area is different. Pleated filters increase the ability of a filter to capture and retain airborne particles, which is why pleated furnace filters are often highly recommended for use in home furnaces.
What Kind of Filter Should I Really Buy?
While the best filter to buy will depend greatly on the size you need and the specific model of furnace it will be installed into, there are some general rules of thumb that can help you get the most for your money. Here at Dan the Filter Man, we typically recommend a polyester or cotton filter with a pleated construction for a good balance between filtration efficiency, holding capacity, and affordability. A MERV rating of at least 8 is suggested as the minimum for home furnaces in Canada, with MERV ratings of 10 or higher recommended for anyone with allergies or respiratory sensitivities.
We hope you find this information helpful, and use it to ensure that you get the best value for your money when shopping for furnace filters, as well as the ideal level of air filtration for your home to keep your living spaces clean and fresh. You can breathe a little easier when you use these tips from Dan the Filter Man!
