Lennox AC Unit Filter Location: A Comprehensive Guide To Finding And Replacing Air Filters

Locating and replacing the air filter in your Lennox air conditioning unit is crucial for optimal indoor air quality and efficient system operation. A well-maintained filter protects your HVAC system, prolongs its life, and improves comfort. This guide details how to find the filter location on various Lennox AC models, outlines types of filters, and provides expert tips for easy maintenance in American homes.

Summary Table: Lennox AC Filter Locations By System Type

Lennox System Type	Typical Filter Location	Access Method	Common Filter Size
Split Central Air (with Furnace)	Near furnace blower, inside return duct/plenum	Remove access panel or pull-out slot	16x25x1, 20x25x1, 20x25x4
Package Unit	Return air grill or inside equipment cabinet	Open filter door on unit or vent grill	Varies; check manual
Air Handler Unit	Below or beside air handler housing	Slide-out tray or removable panel	Standard or custom sizes
Ductless Mini-Split (Lennox MPB/MLA)	Behind front cover of indoor unit	Lift and open cover panel	Washable mesh filter

Importance Of Locating And Replacing The Lennox AC Filter

Regular filter replacement is essential for improving airflow, protecting critical HVAC components, and reducing allergens and dust in the home. Dirty or incorrectly installed filters can lead to system breakdowns and higher energy bills. Knowing the exact filter location prevents unnecessary service calls and ensures timely replacement.

Understanding Lennox AC Systems: Types And Their Filter Locations

Lennox manufactures various AC system types, each with its unique filter placement. Homeowners must recognize their unit model to find and replace the filter correctly. Below are the main categories and where to commonly find the filters:

Split Central Air Conditioner With Furnace

This configuration is prevalent in U.S. homes. The air filter is usually inside or near the furnace, typically in the blower compartment, return air plenum, or side-mounted filter rack. Look for a slot with a removable cover, often located just where the return duct connects to the furnace.

Lennox Package Unit

Package units combine heating and cooling into one box, often placed outside or on rooftops. In most Lennox models, the filter is accessible through a dedicated filter access door on the unit itself, or through the return air vent grille. Unit stickers or manual diagrams identify the filter slot’s location.

Air Handler Units (AHUs)

For homes with a heat pump or straight-cooling system and no gas furnace, a Lennox AHU is common. Here, the filter is usually installed beneath or beside the AHU, in a slide-out tray or removable panel. The setup may vary based on installation configuration.

Ductless Lennox Systems (Mini-Split)

If you have a Lennox ductless system, such as the MPB or MLA mini-split, the filter is behind the front cover of the indoor wall unit. You can easily access it by lifting or snapping open the main panel without tools.

How To Identify Your Lennox AC Unit Model

The location of your filter often depends on your specific Lennox model. To find the unit’s model number, check the nameplate on the outdoor condenser, inside the furnace cabinet, or on the main body of the air handler. Once identified, consult the unit’s manual for model-specific filter locations and instructions.

Step-By-Step: Locating The Filter On A Lennox Central AC Furnace System

1. Turn Off The HVAC System: Before servicing, set your thermostat to OFF and disconnect power at the breaker panel or furnace switch for safety.
2. Locate The Blower Compartment: Most Lennox units have a filter slot near the blower, where cold return air enters the furnace. Look for a removable door or metal cover—often labeled “FILTER”.
3. Check The Return Air Duct: Some installations place the filter in a rack inside the main return air duct, next to or above the furnace. Inspect the ductwork for a dedicated filter slot or tray.
4. Remove The Old Filter: Slide out the existing filter, noting its orientation (airflow arrows), and check the dimensions printed on the frame.
5. Install The New Filter: Place the new Lennox-approved filter in the same direction. Make sure it fits snugly; a loose filter can allow dust to bypass and damage the system.

Filters are typically changed every 1–3 months for standard disposable models, or cleaned monthly for washable brands.

Lennox Package And Air Handler Filter Locations: Quick Reference

• Package Rooftop/Outdoor Unit: Look for a separate access panel labeled “FILTER” on the unit’s side; some units require a screwdriver to open.
• Indoor Air Handler (No Furnace): Find a slide-out tray or vertical rack in the return air section directly below or beside the unit.
• Wall And Floor Return Grilles: In older or customized homes, the main return vent in a hallway or ceiling may house the air filter. Open the grill by turning the latch or removing screws.

Always double-check specifications on the filter size and type before shopping for replacements, as incorrect dimensions can restrict airflow or allow debris through.

Ductless Lennox Mini-Split Filter Location And Maintenance

The Lennox MPB and MLA ductless models use washable mesh filters to trap dust. To locate:

• Lift the front panel of the indoor wall unit by gently pressing the side tabs or using a fingernail groove.
• Slide out the mesh air filter; it may be split into two removable halves for larger models.
• Rinse the filter under lukewarm water (no soap); let it air-dry completely before reinstalling.

Clean these at least once per month or more frequently in dusty environments.

Best Practices For Lennox AC Filter Replacement

Expert HVAC technicians recommend the following filter replacement practices to prolong system life and maintain healthy indoor air:

• Check filters monthly during heavy use (summer or winter).
• Replace filters every 60–90 days for typical households, or 30 days if there are pets/allergies.
• Write the replacement date on the filter frame for easy tracking.
• Always check airflow arrows when installing—the arrow points toward the furnace or air handler.
• Select filters with the correct Minimum Efficiency Reporting Value (MERV) as recommended by Lennox for your model and indoor air quality needs.

Lennox Filter Types And Sizes: What Homeowners Need To Know

Lennox AC units use a variety of **filter types**:

• Disposable Pleated Filters (1″ or 4″ thick): Most common; higher MERV ratings available for improved allergen control.
• Washable Electrostatic Filters: Reusable; must be cleaned and dried monthly.
• HEPA Or High-Efficiency Filters: Some high-end Lennox systems, like the PureAir air purifier, require specific cartridge filters that trap microscopic particles and VOCs.

Check your user manual or the old filter for the correct size, usually printed on the frame (e.g., 16x25x1 inches).

Frequently Asked Questions On Lennox AC Filter Location

Where Is The Filter On My Lennox Air Conditioner?

Central systems: The filter is often found at the furnace/air handler in a return air plenum or blower compartment. Package units: The filter typically sits behind the access door on the unit’s side or at the return air vent.

How Often Should I Change My Lennox AC Filter?

For most households: every 60–90 days, or more often with allergies, pets, or lots of dust. Inspect the filter monthly and replace or clean when visibly dirty.

What Happens If I Can’t Find My Filter?

Check all accessible return vents, the furnace/air handler compartment, and consult your Lennox owner’s manual (available online by model). If still unsure, contact a licensed HVAC technician for assistance.

Can I Use Off-Brand Filters In My Lennox AC?

Lennox recommends using OEM filters for premium performance, but properly sized high-quality aftermarket filters are generally compatible. Always match size and MERV rating with system specifications.

Expert Tips: Making Lennox AC Filter Maintenance Easy

• Keep extra filters on hand for quick changes every season.
• Use a smartphone calendar reminder for monthly filter checks.
• Mark air flow direction on filter housing with a sticker or marker for reference.
• When in doubt, snap a photo of your filter setup and show it to a local HVAC supplier for matching replacements.

Common Lennox Filter Sizes Table

Filter Size (Inches)	Common Use
16 x 25 x 1	Furnace/air handler side mount
20 x 25 x 1	Return air plenum/furnace rack
20 x 25 x 4	High-efficiency/HEPA applications
Custom Sizes	Custom installations/multi-return systems

Professional Lennox Maintenance: When To Call An HVAC Technician

Even with easy filter access, professional inspection is advised annually for deep cleaning and to check for hidden airflow blockages, duct leaks, or faulty installation. If you notice low airflow, odd smells, or persistent dust even after filter change, it’s time for expert service.

Resources For Lennox Homeowners

• Lennox User Manuals & Filter Guides
• Lennox Dealer Locator
• Energy.gov AC Maintenance Tips

For Lennox units under warranty, always use certified filters and document service dates to keep your coverage intact.

Key Takeaways On Lennox AC Filter Location

• Filter access varies by model: Verify your system type before searching for the filter slot.
• Central air/furnace combos place filters at or near the air handler or return duct.
• Package units have filter doors on the unit exterior or at return grilles.
• Ductless Lennox mini-splits place washable filters directly behind the indoor unit panel.
• Correct filter replacement enhances air quality, boosts system efficiency, and protects your home investment.