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Air Filters vs. Furnace Filters: Key Differences for Cleaner Air
In the hidden world of your central air system, two filters quietly take on crucial roles. One works tirelessly to trap allergens and dust, refreshing the air you breathe. The other, like a shield, stands guard at your furnace, blocking debris that could wreak havoc on your heating system. This isn’t just a simple team-up—it’s a strategic partnership where both filters play unique, irreplaceable parts. Your central air system uses two separate filters for a reason: one for air purity and one for mechanical protection.
Though they may seem similar, the battle of air filters vs furnace filters goes far beyond appearances. Each filter has its own mission and its own way of keeping your home running smoothly. One ensures the air is crisp and clean, while the other defends the heart of your heating. Together, they shape the air you breathe and the heat you feel, creating harmony in the background of your home’s comfort.
Key Takeaways
- Indoor air quality improves with air filters, while furnace components receive protection from furnace filters.
- Air filters better capture small allergens, whereas larger particles get trapped by furnace filters.
- Higher efficiency often characterizes air filters, requiring a greater Minimum Efficiency Reporting Value (MERV) rating.
- Air filters require more frequent replacements than furnace filters, as their main goal is improving air quality.
- Recognizing these distinctions aids homeowners in selecting the right filter type for specific needs.
The Key Difference Between Return Air Filters & Furnace Filters
Return air filters and furnace filters share a common mission but with their own rhythm—capturing dust and debris as air moves through your home, clearing the way before it reaches the heart of your HVAC system. Every time your system hums to life, these filters are hard at work, quietly keeping the air clean and your equipment protected.
It is important to note that because the filtration process is the same between air and furnace filters, some homes utilize a single filtration system or type of air filter for both heated and cooled air. There won’t always be a specific spot for a furnace filter in some central air systems. When this is the case, the air filter is sometimes referred to as a “whole home air filter.”
Central HVAC systems and newer heat pump systems are often designed so that the heating unit and cooling unit share the same air handler and intake vent air filters.
That being said, air filters and furnace filters are not the same thing.
Across countless homes, heating and cooling work in tandem yet follow separate paths, each with its own filter playing a distinct role. While the cooling system relies on one filter to purify the air, the furnace demands its own dedicated protector—a filter designed specifically to guard against the debris that threatens its inner workings. Two systems, two filters, one goal: keeping your home comfortable and efficient year-round.
Differences start to occur between furnace filters and AC filters in older homes or homes with special heating and cooling needs (like those in New England, where winter weather is much more prominent than here in Alabama).
While both the air filter and furnace filter serve the same function – to clean the air in your home – features like the filter location, lifespan, filtration level, and cost are the key differences.
AC Air Filters
Here are features that are specific to home AC intake air filters.
Air Filter Location
AC air filters are often located in a slot behind the air return vent. The vent can be in several places in a home. Typically, they are along a staircase, in a hallway, or on the ceiling in a main room in the house.
Air Filter Function
The primary functions of an AC air filter include:
- Clears contaminants, allergens, bacteria,viral particles, dust, mites, and debris from the cooled air
- Helps the AC system run efficiently
- Protects the AC equipment from harmful contaminants
Air Filter Lifespan
An AC air filter’s lifespan is a reflection of your home’s unique rhythm—how often the system hums, who walks through the door, and the daily habits that shape the air inside. In most cases, these filters quietly do their job for about 1 to 3 months before needing a fresh start, whether through replacement or a good clean.
Air Filter Filtration Level
AC air filters shine when it comes to filtration power, capturing everything from hefty dust particles to invisible viruses drifting through the air. Their range is vast, tackling the big and the microscopic with precision. The filtration level is noted as a MERV rating from 1 to 20. The higher the MERV number, the more air filters can clear. AC air filters usually have a rating between 8 and 13 MERV.
Air Filter Cost
Pleated, fiberglass AC air filters, recommended for most home AC systems, range from less than $6 to $50 apiece. It all depends on the size, thickness, and MERV rating.
Furnace Filters
Below are the key features that differentiate a furnace filter from an AC air filter.
Furnace Filter Location
Tucked inside the furnace’s blower compartment, furnace filters quietly get to work. You’ll find them in a tray or behind a door, positioned near the heart of your home’s heating system, ready to catch debris before it causes trouble. Nestled close to the air intake vents, these filters stand guard, ensuring smooth airflow and clean operations from the inside out.
Furnace Filter Functions
A furnace filter’s mission mirrors that of its AC counterpart, but it tackles the warmth in your home instead of the cool. As heated air flows through, the filter:
- Traps contaminants and debris in the toasty air
- Keeps your heating system running smoothly, free of clogs
- Shields your furnace from harmful particles that could disrupt its operation
Furnace Filter Lifespan
Furnace filters come with different lifespans, all depending on their thickness. The slim 1-2” filters work hard but need swapping or cleaning every 1-3 months. Step up to a 3-4” filter, and you get up to nine months of protection. The hefty 6” filter? It holds steady for a full year, quietly doing its job without missing a beat.
Furnace Filter Filtration Level
Furnace filters also use the MERV rating scale to denote filtration level. Residential furnace filters are usually between 4-12 MERV.
Furnace Filter Costs
The price of a furnace filter dances between $15 and $25, but the cost is as layered as the filter itself. Thicker filters, or those with higher MERV ratings, come with a heftier price tag, reflecting their added power to capture even the smallest invaders in your air. Every extra dollar brings a bit more filtration muscle to your home’s heating system.
Air Filters vs. Furnace Filters Quick Guide
AIR FILTERS | FURNACE FILTERS | |
|---|---|---|
| System | Used for cooling systems and modern central air systems with integrated cooling & heating | Used in heating systems that require dedicated filtration |
| Core Functionality | Core Functionality | Clears contaminants, allergens, bacteria, viral particles, dust, mites, and debris from the air |
| Location | Usually at 2 points in a house behind the air intake vent | Located in a tray or door on the air handler box |
| Filtration Level | MERV Ratings 1 - 20 | MERV Ratings 4 - 12 |
| Replacement Time | Recommended every 90 days, but sooner depending on usage, pets, and number of residents | Recommended 1 – 3 months for furnace filters up to 2” thick, up to 9 months for thicker furnace filters |
| Filter Cost Range | $6 - $50 per filter depending on size and MERV rating | Usually between $15 - $25 per filter |
Air Filters & Furnace Filters for Any Home
If you need a replacement air or furnace filter, shop with Filterbuy and get your new air filters delivered to your door. Filterbuy offers custom air filter sizes as well as air filter subscriptions.
Or you can start by selecting your preferred MERV rating below.
MERV 8 AIR FILTERS 
MERV 11 AIR FILTERS 
MERV 13 AIR FILTERS Frequently Asked Questions
Are furnace filters and air filters the same?
Furnace filters and air filters serve similar purposes but aren't the same. Furnace filters are explicitly made for HVAC systems to clean air in heating systems, while air filters can be used in various applications like air purifiers or standalone AC units. Although some may be interchangeable, using the right filter for your furnace or HVAC system for optimal performance is essential.
Do I need both a furnace filter and a return air filter?
Most HVAC systems only require one filter, usually located at the return air vent, to capture particles before the air reaches the furnace or AC. If your system has separate filters, make sure to check and replace them as needed. Always consult your system's manual for the best filtering practices.
Does the furnace have an air filter?
Yes, furnaces have air filters that capture dust, allergens, and other particles, improving air quality and protecting the furnace. Regularly check and replace the filter to avoid clogs, which can affect performance and air quality.
Do furnace filters purify air?
Furnace filters do purify air by trapping dust, pollen, and other particles, but their effectiveness depends on the filter type. For better air purification, consider using high-efficiency filters or adding an air purifier to your setup.
How often should I replace my furnace filter?
Replace furnace filters every 1 to 3 months, depending on the filter type and household conditions. Homes with pets, allergies, or excess dust may require more frequent changes. Check the filter monthly to ensure it's not clogged, and replace it as needed for efficiency and air quality.
Do AC and heater use the same filter?
Yes, most centralized HVAC systems use the same filter for both heating and cooling. The filter is typically located in the air return duct. Be sure to replace it regularly to maintain optimal performance year-round.
What happens if you install a furnace air filter backward?
Installing a furnace filter backward can obstruct airflow, reducing efficiency and potentially damaging your system. For proper installation, always follow the airflow direction indicated by the arrow on the filter.
Do all HVAC systems have two filters?
Not all HVAC systems have two filters. Many have one filter that serves both heating and cooling. However, some systems may have separate filters. Check your system's manual or consult a professional to find out how many filters you need to maintain.
How many air filters does a house have?
Most homes with a central HVAC system have one filter, but larger homes or homes with multiple systems may have several. Filters may also be in ductless units or air purifiers. Check all relevant systems to know your home's exact number of filters.
Where is my furnace filter located?
The furnace filter is typically located in the return air duct or near the blower compartment. It may be behind a cover or grille. If you're unsure, consult your HVAC system's manual or a professional.
Does central AC use a furnace filter?
Yes, central AC systems usually use the same filter as the furnace. The filter cleans the air before it's cooled and circulated. Regularly replacing the filter ensures efficiency and good indoor air quality.
Can I run my furnace without an air filter?
Running a furnace without an air filter is not recommended. The filter protects the furnace from dust and debris, maintaining efficiency and preventing damage. Operating without one can reduce air quality and lead to costly repairs. Always use a clean filter.
