HVAC Basics: HVAC System Air Filters
By Anne Fonda with expert review by Sean Goddard, Product Manager, Coils & Indoor Air Quality
HVAC filters help remove dust, dander, and harmful particles from the air inside your home. You may know them by the name furnace filter or air conditioner filter. You may have only one HVAC air filter, but it’s possible that you have more than one.
By regularly changing your filter, you can improve your indoor air quality and extend the life of your heating and cooling system.
How to change an air filter
Changing your HVAC and furnace air filter is a vital part of home maintenance. To help ensure you're breathing healthier air and supporting your heating and cooling system to operate at an optimal level, follow the simple steps in this video to change your furnace filter as suggested.
Where to find your HVAC filter
Locating your HVAC air filter or filters is the first step. If you have a traditional split system, check at the furnace or air handler inside your home. You may see a 1” or 4” slot to the side of the indoor unit. That’s where the air filter is located. It could be behind a door or panel. You may also have an air filter located behind a large return air vent in the ceiling or an interior wall.
If you have a packaged system, there may be a filter located inside the outdoor unit, but your main air filter will most likely be inside the home behind a large return air vent in the ceiling or an interior wall.
What does a filter do?
Filters help protect the many parts of your heating and cooling unit from debris and buildup that can shorten the working life of the system. A clogged air filter can cause:
- Reduced airflow
- Frozen evaporator coil
- System overheating
- Decreased energy efficiency
- Increased energy bills
- Need for early repairs
- Early system failure
A properly fitted filter can also trap unwanted, and oftentimes unseen, pollutants from the air in your home, including:
Dust & Dirt
Pollen
Mold
Fiber & Lint
Pet Dander
Bacteria
Changing your return vent filter
Start with the return vent filter, if you have one. Air filters are typically found behind a large return vent door, often located in the ceiling or wall in the central portion of your home. If your home has multiple HVAC systems, there will likely be at least one air filter for each unit.
Changing your furnace filter
Another filter location for most HVAC systems is next to the furnace or air handler. The indoor unit houses the fan and fan motor and is usually located in the basement, crawlspace, attic, or utility closet. A slim, removable cover will reveal the filter location.
How often should I change my air filter?
In general, plan on replacing your HVAC air filter every 30-90 days.
“At a minimum, change the air filter every 1-3 months. A great way to think about this is the first day of every month or the first day of a new season. If you have pets or it’s pollen season, you may want to change it more often.”
- Sean Goddard, Product Manager, Coils & Indoor Air Quality
Which way does the air filter go? Follow the HVAC filter arrow
Not every AC or furnace filter will have an arrow printed on the frame, but when it does the arrow indicates the direction the filter must face. The arrow should face the direction the air is flowing. When changing the AC or furnace filter, the arrow should face the furnace and point away from the return duct. The same is true when changing the return air duct filter. The arrow should point toward the unit (into the ceiling or into the wall).
LET'S CLEAR THE AIR
Trane Comfort Performance Filter
Air filters remove dust, lint, pet dander, and other pollutants so you can breathe easier knowing your indoor air quality is better with Trane®. Compatible with Trane systems or any standard HVAC system
What’s the best HVAC filter?
Air filters are measured by Minimum Efficiency Reporting Values (MERV). A MERV rating speaks to the filters ability to capture large and small particles. The higher the MERV rating, the better the filter is at capturing specific pollutants from the air. However, a higher MERV rating may not be best for your system.
The MERV scale rates filters from 1 to 16. Your AC or furnace is designed for a specific type of filter. Most homes are best served by a filter with a MERV rating of 8 to 13, but refer to your system's user manual or consult a Trane dealer for guidance.
| MERV rating | Pollutants removed from air |
|---|---|
| 1-4 | Pollen, dust, clothing and carpet fibers |
| 5-8 | Pollen, dust, clothing and carpet fibers, hair spray, mold spores |
| 9-12 Best for Pets | Pollen, dust, clothing and carpet fibers, hair, mold spores, legionella, pet dander |
| 13-16 Best for most tobacco smoke | Pollen, dust, clothing and carpet fibers, hair spray, mold spores, bacteria, pet dander, cooking oil, most tobacco smoke, smog |
Best for Pets
Best for most tobacco smoke
HVAC Air Filter FAQs
Air filters should be changed at least every 90 days unless otherwise indicated on the packaging or by the manufacturer.
If you (or the previous homeowner) has been using the right size of filter, you should be able to remove the existing filter and see the size dimensions printed on the filter frame. If you don’t see measurements listed, you can measure the filter slot for height, depth, and width, and round up to the nearest inch.
In order for the filter to work properly, the right size is crucial. Using a filter that's too small or too large will allow debris particles to pass into the HVAC unit, potentially damaging or blocking the system. Purchase the correct size and replace the filter as soon as you can.
The MERV rating is typically printed on the filter packaging, but not necessarily on the filter itself. If you need assistance determining the best filter for your unit, a Trane dealer would be happy to assist you.
To clean a reusable filter, remove the filter from the air cleaning device. Follow the directions for your filter – you should be able to find directions online or in the installer's guide for your device. General directions: Soak the filter in warm water in a bathtub or sink. Use dish soap and a soft-bristle brush or sponge to remove stuck-on debris. Thoroughly rinse the filter. Allow the filter to completely dry before returning it to the device.
ADVANCED INDOOR AIR QUALITY
A breath of fresh air
Air filters are the first defense against the pollutants in your air, but building a complete air filtration system can help support better indoor air quality (IAQ). Trane® Indoor Air Quality solutions can help remove harmful contaminants from the air you breathe.
*Based on third party testing of particle removal efficiency down to 0.3 microns (2005).
Anne Fonda, Content Writer
A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.
She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism.
When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.
Get helpful HVAC tips in our newsletter
Sign up for our email newsletter to learn helpful HVAC tips and tricks before your purchase your system.Related articles
Contact a local dealer
Dealers can answer questions, help you find the right products for your home, and repair your system.
We’re here to help
Connect with our Customer Care team about your products, warranties, and dealer concerns.
Available Monday – Friday from 7am to 5pm CST
A phone