We may not give it much thought, but the quality of your indoor air is important. Allergies, illnesses, and the structure of your home can be at stake. Not only can our indoor air make us ill, but the spread of dust and mold can jeopardize your air ducts, damage your HVAC system, and ruin other portions of your home.
Regular HVAC maintenance and furnace filter replacement will dramatically improve indoor air quality (IAQ), as well as save you money on HVAC repair or replacement. There are excellent choices for furnace filters on the market. Explore some of our most frequently asked questions on furnace filters.
Use this quick reference list to jump to each section:
- How Does a Furnace Filter Work?
- What are Your Furnace Filter Needs?
- What are the Types of Furnace Filter Materials?
- What are Popular Furnace Filter Sizes?
- How is a Furnace Filter Measured?
- What is a MERV Rating?
- Are There HEPA Furnace Filters?
- Are There Furnace Filters for Allergies/Smoke/Pets?
- Can You Clean, Wash, or Vacuum a Furnace Filter?
- Where is my Furnace Filter Located?
- Which Way Does a Furnace Filter Go?
- When Should I Replace a Furnace Filter?
- Can a Furnace Filter Be Cut to Size?
- Will a Furnace Run Without a Filter?
- What Does MPR Stand For?
- Can a Dirty Furnace Filter Cause Headaches?
- Still Have Questions?
How Does a Furnace Filter Work?
Furnace filters protect the blower fan and coils from dirt, debris, hair, and other household particulates from accumulating throughout your system and air ducts. The pleated and sometimes electrostatically charged material helps to capture and hold those contaminants against the filter until it is time to replace the old one.
What Are Your Furnace Filter Needs?
Depending on your needs, allergies, odors, and pets, you will want to purchase and select the right furnace filter for your home and indoor air quality.
- Material: Most fiberglass filters provide minimal protection to your HVAC system and allow a number of allergens to pass through the filter. Protect your system from costly repairs and dirt accumulation while cleansing your indoor air with a pleated air filter. Pleated air filters are denser and provide adequate protection to the blower fan, coils, and air ducts. Electrostatically charged pleated filters are preferred for homes with pets, smokers, and allergy sufferers.
- MERV or MPR Rating: Review the MERV rating for the filter brand. The higher the MERV rating, the better the filter is at removing allergens and particulates. If you’re considering one of the 3M Filtrete filters, review the MPR rating that works best for you.
- Size: Furnace filter sizes vary according to the type of HVAC system you have. Find the recommended size through the HVAC manufacturer’s manual, or locate the previous filter dimensions used in the system.
What are the Types of Furnace Filter Materials?
- Non-Pleated/Fiberglass: One of the most recognizable fiberglass filters is the basic blue filter you find in most stores. While they can capture large pieces of debris, they are not effective at removing fine dust and other harmful allergens and contaminants that can collect and build up inside HVAC systems.
- Pleated: Pleated filters are strong, thicker, and remove indoor air particulates better than fiberglass. Offering a higher MERV rating—typically around MERV 12—they can also be electrostatically charged, capable of capturing even more indoor air particulates, such as dust mite debris, bacteria, and odors. Pleated filters are best for allergy-sufferers, homes with pets, and indoor smokers.
What are Popular Furnace Filter Sizes?
There is no standard furnace filter size, as many systems take different sizes. However, the most popular sizes we see are 16 x 20, 16 x 25, 20 x 20, and 20 x 25.
How is a Furnace Filter Measured?
Select the correct furnace filter based on the size of your HVAC system. The best way to determine the correct filter size is to look at the dimensions on the old furnace filter, usually indicated and measured by width and length (W x L), as well as thickness. In the case of furnace filters, length and height are used interchangeably.
The thickness (or depth) of the filter(s) comes in 1-, 3.75-, 4-, and 5-inch thicknesses. Lastly, the thicker the furnace filter, the longer the filter will last. However, it is important to check the compatibility of your HVAC system with any replacement furnace filter before purchasing.
What is a MERV Rating?
The Minimum Efficiency Reporting Value (MERV) rating on a furnace filter measures the effectiveness of the filter in capturing allergens and particulates. Developed by the American Society of Heating, Refrigeration, and Air Conditioner Engineers (ASHRAE), this rating provides a breakdown of filtration between 1 – 16.
MERV 16 filtration is efficient at removing 95% of particulates down to 0.3 – 1.0 microns while removing 90% of particulates down to 3.0 – 1.0 microns. AHSRAE recommends furnace filters rated MERV 6 and up, while the US Department of Energy recommends MERV 13. If you live in a LEED-certified home, you may want a filtration of MERV 8 or better.
- MERV 1 – 4: Efficient for removing 20% or less of particulates between 3.0 – 10.0 microns, these furnace filters remove particulates such as pollen, dander, lint, and other similarly large debris or particles.
- MERV 5 – 8: Depending on the MERV rating, these filters are great at removing 20% - 85% of indoor air particulates between 3.0 - 10.0 microns. The percentage of particulates captured increases as the MERV rating goes up, removing contaminants such as mold spores, dust, lint, dander, and allergens such as pollen.
- MERV 9 – 12: If you desire filtration for antimicrobial, household dust, bacteria, and outdoor air pollutants, furnace filters with a MERV rating between 9 – 12 are ideal. Nordic Pure furnace filters offer a range of mid to high MERV-rated filters.
- MERV 13 – 16: Remove the smallest indoor air allergens with these MERV-rated filters. They remove a high range of particulates—bacteria, viruses, odors, smoke, mold, microscopic allergens—and are ideal for clinics, hospitals, and other medical facilities. Using electrostatic pleated filters, these filters can remove between 75% - 95% of allergens and particulates between .3 – 1.0 microns.
Are there HEPA Furnace Filters?
Unfortunately, HEPA filters are not rated for HVAC or furnace usage because the increased airflow resistance would put too much strain on the system and blower. The thickness and decreased airflow would damage the HVAC system.
However, there are furnace filters with a MERV rating that is close to the filtration of a HEPA filter. Review filters with a MERV 12 - 14 rating. Other features to review include:
- Pleating: Pleated filters, as opposed to fiberglass, contain more surface area for catching particulates--allergens, dust, hair, or dander--in the folds. Also, the accordion shape allows you to reduce the number of filter changes.
- Activated Carbon: In addition to the pleats on the filter, activated carbon helps to remove a miasma of odors from your indoor air--pet odors, cooking, or smoke.
Are There Furnace Filters for Allergies/Smoke/Pets?
Specific furnace filters can help you clean and maintain your indoor air quality, whether you suffer from allergies, pet dander, or need odor removal. Keep these specifics in mind when shopping for furnace filters:
- Allergies: Usually, a MERV 8 furnace filter will suffice for allergy-sufferers; however, if allergies—anything from environmental pollutants to your pets—make you suffer, consider a MERV 13 or higher-rated filter. Furnace filters with a MERV 13 or higher rating are great for removing candle soot, vehicle exhaust, and other indoor air allergens and particulates.
- Pets: To effectively mitigate pet dander and odors, look for a filter with a minimum MERV 8 rating. These filters are typically pleated, and they will indicate their effectiveness against pet dander. To combat pet dander and odors, look for filters with a MERV 10 rating.
- Smoke: For those who live in smoke-ridden homes—or homes that have smokers—a MERV 12 or higher-rated furnace filter will work best. Designed with pleated material and usually with an electromagnetic charge, these filters easily remove not just dust, but also take residual smoke odors out of the air.
The 3M Filtrete Home Odor Reduction filter with an electrostatically-charged pleated filter and activated carbon provides superior cleaning for allergy-sufferers.
Can You Clean, Wash, or Vacuum a Furnace Filter?
Washable furnace filters are available for HVAC systems, but their effectiveness may vary from household to household. Homes with allergy sufferers may find that washable filters pose a risk to their health. Washable furnace filters should be thoroughly dried prior to reusing, as any residual moisture can encourage mildew and mold growth that can travel through the ductwork and into the remainder of the home.
Vacuuming alone may not be enough to remove accumulated dust from a washable filter, as most will require a rinse or wash to remove any excess dust.
Where is my Furnace Filter Located?
Filters are usually located near the blower inside the furnace. Remove the door panel and locate the filter near a return duct or the blower.
Which Way Does a Furnace Filter Go?
Furnace filters should always be placed in the proper direction, as indicated by the arrows on the side or edging of the filter. Insert the filter with the air flow arrows pointing toward the blower.
When Should I Replace a Furnace Filter?
See the recommended manufacturer-suggested replacement time, or replace when and as often as needed, depending on usage and indoor air quality.
Can a Furnace Filter Be Cut to Size?
While there are several online videos and tutorials for DIY furnace filters, the rule of thumb would be to measure and use the correct size filter for your HVAC. Specific furnace filter sizes and measurements exist to provide an airtight seal that helps secure the filter into the fitting.
The sizing is also beneficial and crucial to preventing allergens, debris, dirt, and other particulates from sweeping past the filter along the sides. The purpose of a furnace filter is to capture these particulates, and cutting a filter to size defeats the purpose of the filter. In the end, it is best to purchase an exact replacement of your old filter with the same dimensions. Remember, one size does not fit all.
Will a Furnace Run Without a Filter?
The short answer is, yes, you could run your HVAC system without a filter. Without any filter in place, though, you run a risk. Without a furnace filter in place, dust, dirt, hair, and other contaminants travel through the ductwork, collecting and sticking to the duct paneling. Because air is recirculated, the dirt is simply pumped back out in the remainder of the house.
Further, the fine dust can accumulate across condenser coils, which are cold and damp to the touch. This can further complicate matters, as it sticks to the coils while the HVAC system works harder. Lastly, a filter helps keep dirt from blocking the condenser drain that moves moisture outside. This portion is critical, as it helps to dehumidify the air inside your home. A clog to your condenser line can be costly to the entire HVAC system.
What Does MPR Stand For?
Coined and developed by 3M Filtrete, the microparticle performance rating (MPR) indicates a filter’s ability to capture micro-particles between 0.3 – 1.0 in size. The higher the MPR rating on any 3M Filtrete furnace filter, the better the micron removal. You will not find MPR ratings on any other brand of furnace filters, as it is exclusive to 3M Filtrete. We offer a range of 3M Filtrete MPR-rated filters starting from 300 MPR up to 2200 MPR for superb micron removal and clean air.
Can a Dirty Furnace Filter Cause Headaches?
Yes. In fact, a dirty furnace filter can cause a number of problems, both to your health and HVAC system. Headaches are a common issue in homes without proper filter maintenance. Dust is not adequately removed from your indoor air; thus, it remains suspended in the ductwork and air.
Trapped dust, pet dander, odors, bacteria, mold spores, dust mite matter, and more wreak havoc on the immune system. With dirty indoor air, expect to suffer from colds and respiratory infections while aggravating asthma.
Still Have Questions?
Win the war against indoor air pollutants and allergies by maintaining and scheduling regular filter changes and HVAC maintenance. In addition, adding an air purifier may also help assuage allergy symptoms. Check out the air purifier FAQ for more indoor air quality information.
Let us help you find the right furnace filter for your home by calling our knowledgeable sales team at 1-800-934-9194, and visit us at the Sylvane Facebook and Twitter pages.
