How to Change Your HVAC Filter: Step-by-Step Guide for First-Timers

January 11, 2026

To change your HVAC or furnace filter, follow these five steps: (1) Turn off your HVAC system at the thermostat, (2) Locate your filter in the return air vent, air handler, or furnace compartment, (3) Remove the old filter and note its size and the airflow direction arrow, (4) Insert the new filter with the arrow pointing toward the furnace or air handler, and (5) Close the compartment and turn the system back on. Most filters should be replaced every 60 to 90 days, though homes with pets or allergies may need to be changed monthly. According to the U.S. Department of Energy, dirty filters can increase HVAC energy use by 10 to 15 percent.

TLDR

Turn off your HVAC system before changing the filter to prevent unfiltered air from entering
Find your filter behind a return vent, in the air handler, or in a slot near the furnace
Note the filter size printed on the frame (e.g., 20x25x1) and the airflow arrow direction
Install the new filter with the arrow pointing toward the furnace/air handler (direction of airflow)
Replace filters every 60 to 90 days, or monthly if you have pets, allergies, or dusty conditions

Changing your air filter is one of the simplest home maintenance tasks you can do, yet it's also one of the most neglected. If you've never changed a filter before, or if you're a new homeowner figuring things out, this guide will walk you through every step.

Don't worry if this feels intimidating. The entire process takes about 5 to 10 minutes, requires no tools in most cases, and can save you money on energy bills while keeping your indoor air cleaner. According to the U.S. Department of Energy, dirty filters can increase HVAC energy use by 10 to 15 percent.

This guide is for first-time homeowners, renters, anyone who has never changed a filter before, or experienced homeowners who want a refresher on best practices.

The 5 Basic Steps

Turn off your HVAC system at the thermostat
Locate the filter (return vent, air handler, or furnace compartment)
Remove the old filter and note its size and arrow direction
Insert the new filter with the arrow pointing toward the furnace
Restart your system and dispose of the old filter

That's it. Now let's go through each step in detail.

Before You Start: What You'll Need

Required:

A replacement filter in the correct size
Access to your thermostat

Optional but helpful:

Flashlight (if your filter is in a dark area)
Permanent marker (to write the installation date)
Trash bag (for the dirty filter)
Vacuum with brush attachment (to clean any dust around the filter slot)

Step 1: Turn Off Your HVAC System

Before you touch your filter, turn off your heating or cooling system. This is important for two reasons:

Safety: The blower fan won't start unexpectedly while your hands are near the equipment
Air quality: Your system won't pull unfiltered air through the ducts while the filter is removed

How to turn off your system:

At the thermostat: Switch the system to "Off" or set the fan to "Off"
At the furnace: Look for a power switch on or near the unit
At the breaker: If you can't find another switch, turn off the breaker for your HVAC system

Wait a moment after turning off the system to ensure the blower fan has completely stopped before proceeding.

Step 2: Locate Your Air Filter

This is often the trickiest part for first-timers. Your filter could be in one of several locations, depending on your system type and home layout.

Common Filter Locations

Behind a return air vent (most common in homes): Look for a large vent on your wall, ceiling, or floor, typically larger than the supply vents that blow air out. The filter sits behind this grille, which usually has clips or a hinged door for easy access.

In the air handler or furnace unit: If you have an air handler in a utility closet, basement, or attic, the filter may be inside or directly adjacent to the unit. Look for a removable door or slot.

In a filter rack between the return duct and furnace: Some systems have a dedicated filter cabinet or rack positioned between the return air duct and the furnace. This is common in upflow and horizontal systems.

Tips for Finding Your Filter

Check your HVAC system's owner's manual
Look for a hinged or removable panel near your furnace
Search for return vents (they pull air in rather than pushing it out)
If your home has multiple return vents, you may have multiple filters

Step 3: Remove the Old Filter and Note Important Details

Once you've found your filter, carefully remove it. Pay attention to these critical details:

Note the Filter Size

Measure the dimensions of the old filter at its edge. You'll see numbers like "20x25x1" or "16x20x4" which indicate:

First number: Length in inches
Second number: Width in inches
Third number: Depth/thickness in inches

Write this size down or take a photo. Your replacement filter must match these dimensions. If no size is printed, measure the filter's length, width, and thickness with a tape measure.

Note the Airflow Direction Arrow

Every filter has an arrow printed on the frame indicating the direction of airflow. This arrow tells you which way to install the new filter. Before removing the old filter:

Look at which direction the arrow is pointing
Consider marking the direction on the furnace or duct with a permanent marker so you'll always know the correct orientation

Remove the Filter Carefully

Slide the old filter out gently to avoid releasing trapped dust back into the air. If possible, immediately place it in a trash bag to contain the dust and debris.

Pro tip: Hold the old filter up to a light. If you can barely see light through it, or if it appears gray or brown instead of white, it definitely needs replacing. A clean filter should be mostly white or light in color.

Step 4: Install the New Filter

Now comes the important part: installing your new filter correctly.

The Arrow Rule: Always Point Toward the Furnace

The airflow arrow on your filter should point toward the furnace or air handler and away from the return duct. This means:

Air flows from your home → through the filter → into the HVAC equipment
The arrow follows the direction the air travels

Common installation scenarios:

Filter Location	Arrow Should Point
Return vent (wall/ceiling)	Toward the wall/ceiling (into the duct)
Air handler compartment	Toward the blower motor
Horizontal furnace	Toward the furnace
Filter rack	Toward the furnace

Ensure a Snug Fit

Slide the new filter into the slot. It should fit snugly but not be so tight that it bends or buckles. A proper fit means:

No gaps around the edges where air could bypass the filter
The filter sits flat without bowing
The door or cover closes properly

If the filter is loose, air will flow around it rather than through it, defeating its purpose. If it doesn't fit at all, double-check your size measurements.

Write the Installation Date

Many filters have a spot on the frame where you can write the date. Use a permanent marker to mark the date you installed the filter. This makes it easy to know when a replacement is due.

Step 5: Close Up and Restart Your System

With the new filter in place:

Replace any doors, covers, or grilles you removed
Secure any latches or clips
Return to your thermostat and turn the system back on
Listen for normal operation (airflow should sound clear and unrestricted)

Dispose of the old filter properly: Seal it in a plastic bag before putting it in your trash. This prevents dust and allergens from escaping into your home or garage.

How Often Should You Change Your Filter?

The EPA recommends replacing filters every 60 to 90 days for most homes. However, several factors affect how quickly your filter gets dirty:

Replace More Frequently (Every 30 to 60 days) If You Have:

Pets (especially multiple pets or heavy shedders)
Allergies or asthma in the household
Smokers in the home
Ongoing construction or renovation
A dusty environment or live on a dirt road
High HVAC usage (running system year-round)

Replace Less Frequently (Every 90 days or longer) If:

You use thicker 4-inch or 5-inch filters (these can last 6 to 12 months)
Your home is unoccupied for extended periods
You have minimal dust sources and no pets

The Simple Rule: Check Monthly

ENERGY STAR recommends checking your filter every month. If it looks dirty or gray, replace it regardless of when you last changed it. A clean filter is white or light-colored; a filter that needs replacement appears gray, brown, or visibly clogged with debris.

Common Mistakes to Avoid

Installing the Filter Backward

This is the most common mistake. An incorrectly installed filter restricts airflow and makes your system work harder. Always check the arrow and ensure it points toward the furnace.

Using the Wrong Size

An undersized filter lets unfiltered air bypass around the edges. An oversized filter won't fit properly and may bend or buckle. Always match the size printed on your existing filter.

Choosing Too High a MERV Rating

Higher MERV filters capture smaller particles but also restrict airflow more. If your system isn't designed for high-MERV filters, you can reduce efficiency and potentially damage equipment. Most residential systems work well with MERV 8 to MERV 13 filters. Check your owner's manual for recommendations.

Forgetting to Replace Regularly

A clogged filter doesn't just reduce air quality; it strains your HVAC system, increases energy costs, and can lead to premature equipment failure. Set a recurring reminder on your phone or calendar.

Running the System Without a Filter

Never operate your HVAC system without a filter in place. The filter protects your equipment from dust and debris that can damage the blower motor and other components.

Understanding Filter Sizes

Filter sizes can be confusing. Here's what you need to know:

Nominal vs. Actual Size

The size printed on filter packaging is the "nominal" size, which is rounded to the nearest inch for convenience. The actual filter is typically ½ inch smaller in each dimension.

Example:

Nominal size: 20x25x1
Actual size: 19½ x 24½ x ¾

When shopping, use the nominal size. A filter labeled 20x25x1 is designed to fit a slot that measures approximately 20 x 25 inches.

Common Residential Sizes

Some of the most popular sizes include:

16x20x1 and 16x25x1 (very common)
20x20x1 and 20x25x1 (very common)
14x20x1 and 14x25x1
12x12x1 (smaller systems)
4-inch and 5-inch deep filters (for media cabinets)

Aerterra offers a wide selection of sizes including 16x20, 16x25, 20x20, 20x25, and many more in both 1-inch and 4-inch depths.

Choosing the Right MERV Rating

MERV (Minimum Efficiency Reporting Value) indicates how effectively a filter captures particles. Higher numbers mean better filtration, but also more airflow resistance.

MERV 8: Good for general household dust, pollen, and mold spores. Works well with virtually all HVAC systems.

MERV 11: Better for pet dander, finer dust, and some bacteria. Ideal for homes with pets or mild allergies.

MERV 13: Excellent for smoke, smog particles, and virus carriers. Recommended by ASHRAE for improved air quality, but verify your system can handle this rating.

Aerterra offers filters in MERV 8, MERV 11, and MERV 13 to match your needs and system capabilities.

The Sustainability Angle: Why Your Filter Choice Matters

Every time you replace an air filter, you're making an environmental choice. Traditional filters made from synthetic materials end up in landfills, where they take decades to decompose.

A More Sustainable Approach

Aerterra filters offer an eco-friendly alternative:

Renewable materials: Made from USA-grown corn rather than petroleum-based synthetics
American manufacturing: Produced domestically, reducing transportation emissions
Nanofiber technology: Effective particle capture without compromising on performance
Reforestation support: Every purchase supports tree planting through the One Tree Planted partnership

When you need to change your filter every 60 to 90 days, those choices add up. Choosing filters made from renewable materials is a simple way to reduce your environmental footprint without sacrificing air quality.

Aerterra Product Spotlight: Never Forget a Filter Change Again

Now that you know how to change your filter, the challenge becomes remembering to do it consistently. Aerterra's subscription service solves this problem:

How it works:

Choose your filter size and MERV rating
Select your delivery frequency (every 1, 2, or 3 months)
Filters arrive automatically with free shipping
Adjust, pause, or cancel anytime

Benefits:

No more forgetting filter changes
No emergency trips to the hardware store
Free shipping on every delivery
Filters made from renewable, American-grown corn materials
Support reforestation with every purchase

Browse Aerterra's filter selection to find your size, or learn more about our story and commitment to sustainable air filtration.

Troubleshooting Common Issues

"I can't find my filter"

Check all return vents in your home (they may be on walls, ceilings, or floors)
Look near your furnace or air handler for a removable panel
Consult your HVAC system's owner's manual
Contact an HVAC professional if you're still unsure

"My filter doesn't fit properly"

Double-check the size matches your old filter exactly
Ensure you're not trying to force a 4-inch filter into a 1-inch slot (or vice versa)
Verify the filter isn't installed at an angle

"I hear whistling or reduced airflow after changing the filter"

Make sure the filter is installed correctly (arrow toward furnace)
Check that the filter isn't too restrictive for your system (try a lower MERV rating)
Ensure the filter is properly seated with no gaps

"My filter gets dirty very quickly"

This could indicate ductwork issues or excessive dust sources
Check for gaps in ductwork that allow dust infiltration
Consider if renovation, construction, or environmental factors are contributing
A professional HVAC inspection may be warranted

FAQs

How do I know which direction to install my air filter?

Look for the arrow printed on the filter frame. This arrow should point toward your furnace or air handler, following the direction of airflow. Air flows from your home, through the filter, and into the HVAC equipment. If you're unsure, the arrow should point away from the return vent and toward the blower motor.

Can I run my HVAC system without a filter temporarily?

No. Running your system without a filter allows dust and debris to enter the equipment, potentially damaging the blower motor, coating the evaporator coil, and contaminating your ductwork. If you don't have a replacement filter available, it's better to leave the system off until you can install a new filter.

What happens if I install the filter backward?

A backward filter restricts airflow because the design is optimized for air flowing in one direction. This forces your HVAC system to work harder, increases energy consumption, reduces heating/cooling efficiency, and can potentially damage equipment over time. If you realize the filter is backward, simply remove it and reinstall it correctly.

How can I remember to change my filter regularly?

Set a recurring reminder on your phone or calendar. Write the installation date on the filter frame. Consider a subscription service like Aerterra's automatic delivery, which sends filters on your chosen schedule. Check your filter monthly when you pay utility bills as a memory trigger.

What's the difference between 1-inch and 4-inch filters?

Thickness affects filter capacity and replacement frequency. One-inch filters need replacement every 60 to 90 days (or more often with heavy use). Four-inch filters have more surface area, can capture more particles before becoming clogged, and typically last 6 to 12 months. Your HVAC system must have a compatible filter cabinet for thicker filters.

Is a higher MERV rating always better?

Not necessarily. Higher MERV ratings capture smaller particles but also restrict airflow more. If your system isn't designed for high-MERV filters, you can reduce efficiency, increase energy costs, and potentially damage equipment. For most homes, MERV 8 to MERV 13 provides excellent filtration. Check your system's manual or consult a professional before using MERV 14 or higher.

How do I know if my filter needs changing before the scheduled date?

Remove the filter and hold it up to a light. If you can barely see light through it, or if it appears gray, brown, or visibly matted with debris, replace it immediately. A filter in good condition should appear mostly white or light-colored. Also watch for signs like reduced airflow from vents, increased dust on surfaces, or allergy symptoms worsening.

Why does my new filter look different from my old one?

Filter designs vary by brand and type. Some use electrostatic fibers, others use pleated paper or synthetic media. As long as the size matches and the MERV rating is appropriate for your system, different appearances are normal. Sustainable filters like Aerterra may also look different because they use corn-based materials rather than synthetic fibers.

Additional Resources

For more information on HVAC maintenance and indoor air quality:

Conclusion: You've Got This

Changing your HVAC filter is genuinely one of the easiest home maintenance tasks you can do. Once you've done it once, you'll wonder why you ever felt intimidated.

Remember the essentials:

Turn off the system first
Note the size and arrow direction
Install with the arrow pointing toward the furnace
Replace every 60 to 90 days (or sooner if needed)
Set a reminder so you don't forget

The payoff is real: cleaner air, lower energy bills, and a longer-lasting HVAC system.

Ready to make your next filter change?

Disclaimer

This article is for informational purposes only. For specific HVAC system recommendations, unusual installations, or if you encounter problems during filter replacement, please consult with a licensed HVAC professional. Individual results may vary based on system type, home conditions, and environmental factors. Always refer to your HVAC system's owner's manual for manufacturer-specific guidance. The energy savings and air quality improvements described are estimates based on general industry data and may differ based on your specific situation.

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