All central heating and cooling systems should have an air filter, but some HVAC units make filters harder to locate. The filter is commonly located in a return air grille, within the air handler, or external to the air handler in a filter rack. Your air handler for your HVAC system will always be inside your house — either in your basement, attic, or utility room/closet.
Clean air filters keep energy bills low and help maintain ideal indoor air quality (IAQ).
Where to Look for HVAC Units and Their Air Filters
First, find your air handler (indoor unit of your HVAC system) — it is a large metal box. If you have a basement, the air handler is likely there. Otherwise, it may be in your attic, a utility room (or closet), crawl space, or in your attached garage.
Air filter locations vary by HVAC system, equipment locations, and duct configuration. In horizontal units with the return duct on the side, a filter typically fits in a slot on the intake side of the blower. Vertical air handlers have filters located in bases or duct tracks on the return duct side, which may be either above or below the air handler, depending on the configuration (up-flow or counter-flow).
Alternatively, air filters may reside in return air ceiling or wall grilles. Systems with multiple returns may have filters behind each return grille.
Regardless of location, you should replace HVAC filters monthly in summer and winter during high-demand operation periods. You can stretch out filter replacements to every two to three months during the spring and fall, but inspect them for cleanliness every month.
When you install a new home air filter, write the date on the new filter when you installed it. If needed, take a photo of the filter so that you have a record of its size. Measure if needed.
Buy filters in bulk and when they go on sale to save money and stock up before each major demand season. Ensure the marked airflow direction aligns with the system airflow when installing. Add a task of “change filter” to your seasonal home maintenance routines.
Neglecting your central air filters causes problems. As they fill with particles, they restrict airflow, straining components and reducing efficiency. With less airflow, the system works harder to cool or heat sufficiently. Energy bills may rise. Dirty filters also allow more allergens and contaminants into the ductwork and air.
Replacing a dirty, clogged filter with a clean one reduces workload and maintains indoor air quality. Select a filter the manufacturer recommends to avoid restricting airflow too much. If dirty filters have been left in place for prolonged periods, there’s a good chance your indoor air could benefit from professional duct cleaning services.
HVAC Filter Types
HVAC systems use different types of filters to remove particles, allergens, and pollutants from the air. Selecting the right filter type for your home’s needs and HVAC capabilities is vital for performance and indoor air quality.
Among your options for HVAC filters are:
Inexpensive fiberglass or polyester filters offer minimal filtration and only capture particles bigger than 10 microns.
Made of cotton, polyester, or blends, folded pleats trap more particles while maintaining airflow by expanding surface area.
Media filters with a static charge coating capture smaller particles, down to 3-5 microns, offering good value.
True HEPA filters remove 99.97% of particles down to 0.3 microns like dust mites but restrict airflow the most.
Carbon treated to absorb odors and gases like VOCs works well with a particle filter.
Detect when to replace and can auto-adjust fan speeds when dirty filters restrict airflow.
Talk to your comfort professional during your next HVAC system tune-up about the best filtration for your home’s needs. Increased filtration reduces airflow, so ensure the system can handle upgraded filters per the manufacturer. Proper tight installation with no air gaps is critical, too. Check you have the correct size before purchasing replacements.
HVAC Filter Sizes
HVAC air filters for houses and apartments come in many sizes, but the most common sizes are:
- 12 x 12 in
- 16 x 16 in
- 16 x 20 in
- 16 x 25 in
- 20 x 20 in
- 20 x 25 in
Measure the current filter’s length and width to determine the size needed. Thickness varies from 1 inch to 5 inches. Some air handlers can accept filters of various thicknesses. For example, my HVAC system takes a 16 x 25 inch filter of either 4 inches or 1 inch in thickness (I just have to remove a spacer for the larger thickness).
Filters should list a MERV rating, a number that denotes filter effectiveness at capturing 0.3 to 10 micron particles. MERV ratings range from 1 to 16. Higher means better filtration and improved indoor air quality.
Consult your AC unit or furnace manual or professional to choose the right balance of efficiency and airflow for your system. Improper sizing can cause issues.
You may also see FPR or MPR ratings instead of MERV:
| Rating System | Value Range | Rating Description |
| MERV | 1–16 | Minimum Efficiency Reporting Value |
| FPR | 1–10 | Filter Performance Rating |
| MPR | 1–2,000 | Micro-Particle Performance Rating |
HVAC Filter Pricing
Typical prices for standard-sized HVAC filters are:
- Basic fiberglass: $6–$25
- Pleated: $10–$40
- Electrostatic: $15–$50
- True HEPA: $50–$120+
- Activated carbon: $30–$65
Prices depend on filter quality, effectiveness, brand, and size. Larger or thicker filters cost more. Cheaper basic filters can increase long-term energy and HVAC costs. Better filtration reduces strain and improves indoor air.
Some companies offer permanent washable electrostatic filters that only need replacement every few years. These reduce waste and costs compared to disposables but are generally very restrictive to airflow. Ensure the filter is dried thoroughly before reinstalling to prevent mold. Handy homeowners can incorporate washable filter cleaning with other easy air conditioner maintenance items to keep their systems operating efficiently.
Replacing dirty air filters monthly or as recommended costs little compared to the benefits of HVAC performance, longevity, and air quality. Properly size and install each new filter. Write the date on it as a handy reminder.
Today’s Homeowner Tips
You can often save buying in bulk when on sale or via auto-delivery subscriptions if timed right to avoid gaps between expired filters. Proper timing optimizes efficiency and air quality.
So, Is Changing Your HVAC Filter Really Important?
Changing the filter regularly is critical to the heating and cooling system functioning. Using the right size and type for your model is just as important.
While dirty filters cause problems, clean filters maintain airflow, reduce strain, and allow efficient operation for lower energy costs. Fresh filters also capture more contaminants to improve indoor air quality.
Following the change schedule for your climate and usage ensures efficient year-round heating and cooling. The small cost prevents much larger duct cleaning or HVAC repair/replacement expenses.
Overall, staying on top of changes optimizes performance, reduces strain, lowers energy use, and improves indoor air. Making it part of seasonal HVAC maintenance protects your comfort system and helps keep your family comfortable.
FAQs About Changing HVAC Filters
How often should the HVAC filter be changed?
For moderate use, change your HVAC filter every one to three months and every two to three months with low use, such as in the spring and fall. During times when your HVAC system works harder, such as in the summer and winter, change your filter every month. Follow the filter manufacturer’s schedule.
What if the filter isn’t changed enough?
Dirty, clogged filters reduce airflow, making the system work harder to maintain temperature, leading to higher energy bills, HVAC strain, and poorer indoor air quality. Replacement helps optimize performance.
Can HVAC filters be cleaned and reused?
You can vacuum and clean washable electrostatic filters, but they must be completely dry before reinstalling. Refrain from cleaning and reusing disposable filters, as they become too clogged. Always replace per manufacturer’s directions.
Where can I buy HVAC filters?
Hardware stores, home centers, warehouse clubs, HVAC shops, and online retailers sell furnace filters in standard sizes. Check that it has the correct dimensions and rating for your unit.
How do I know what size HVAC filter I need?
Check the owner’s manual for size and rating specifics. If available, measure the old filter’s length, width, and thickness in inches. Photograph it before buying replacements.
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