Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
Changing the air filter is the one maintenance task on a central heating and cooling system that a householder can do without tools, and it is the task most often skipped. ENERGY STAR asks you to inspect the filter once a month and to change it at least every three months. A blocked filter slows the airflow, raises the running cost, and can damage the equipment.
This page gives the sequence, the two intervals that come from a government source, and the two values that no general source can supply for your equipment. Filter size and the highest efficiency rating your system will accept are specific to your model. Both are marked unverified here on purpose.
Necessary equipment
| Item | Note |
|---|---|
| New air filter | The size must be the same as the used filter. |
| Bag for the used filter | A refuse bag is sufficient. |
| Marker pen | For the date on the frame of the new filter. |
| Flashlight optional | Some filter slots are in a dark space. |
| Screwdriver optional | Only if the cover of the filter slot has screws. |
Specifications
Source: What is a MERV rating? · tier 1 · accessed 2026-07-28
Source: What is a MERV rating? · tier 1 · accessed 2026-07-28
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
Prepare the equipment
Estimated 2 min
SET THE THERMOSTAT TO OFF BEFORE YOU OPEN THE FILTER SLOT.
The blower can start without warning and injure your hand.
- Set the thermostat to OFF.<1mReport a problem with step 1, Prepare the equipment
- Find the filter slot.2mReport a problem with step 2, Prepare the equipment
- The filter slot is usually near the joint between the return duct and the equipment.
- Some systems hold the filter behind a return grille in a wall or a floor.
- The equipment documentation gives the location.
- Put the new filter near the equipment.<1mReport a problem with step 3, Prepare the equipment
Remove the used filter
Estimated 2 min
- Open the cover of the filter slot.<1mReport a problem with step 1, Remove the used filter
Hold the used filter level.
Dust falls from a used filter and can go into the equipment.
- Remove the used filter from the slot.<1mReport a problem with step 2, Remove the used filter
- Examine the frame of the used filter.<1mReport a problem with step 3, Remove the used filter
- Record the size from the frame.<1mReport a problem with step 4, Remove the used filter
- Record the direction of the airflow arrow.<1mReport a problem with step 5, Remove the used filter
Examine the used filter
Estimated 1 min
Source: Maintenance Checklist · tier 1 · accessed 2026-07-28
Source: Heat & Cool Efficiently · tier 1 · accessed 2026-07-28
- Examine the dirty surface of the used filter.Open the source document for this step, efficiency guide from ENERGY STAR, page 7<1mReport a problem with step 1, Examine the used filter
- If the filter is grey and full of dust, decrease the interval between replacements.Open the source document for this step, efficiency guide from ENERGY STAR, page 7<1mReport a problem with step 2, Examine the used filter
- Put the used filter in a bag.<1mReport a problem with step 3, Examine the used filter
Install the new filter
Estimated 2 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
Do not increase the efficiency rating of the filter without advice.
The EPA says that an HVAC technician must find the highest efficiency that your system accepts.
- Make sure that the new filter is the same size as the used filter.<1mReport a problem with step 1, Install the new filter
Make sure that the airflow arrow points to the blower.
A filter in the wrong direction decreases the airflow. This can cause damage to the equipment.
- Turn the new filter until the airflow arrow points to the blower.<1mReport a problem with step 2, Install the new filter
- Put the new filter into the slot.<1mReport a problem with step 3, Install the new filter
- Make sure that the filter is flat in the slot.<1mReport a problem with step 4, Install the new filter
- Make sure that there is no gap at the edges of the filter.<1mReport a problem with step 5, Install the new filter
- Close the cover of the filter slot.<1mReport a problem with step 6, Install the new filter
After the job
Estimated 2 min
- Write the date on the frame of the new filter.<1mReport a problem with step 1, After the job
- Set the thermostat to the usual setting.<1mReport a problem with step 2, After the job
- Make sure that the airflow from the vents is normal.<1mReport a problem with step 3, After the job
- Record the size of the filter and the date.<1mReport a problem with step 4, After the job
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- air filter
- Also called: furnace filter, AC filter, HVAC filter, return air filter, air handler filter, heating filter
- filter slot
- Also called: filter rack, filter cabinet, filter housing, return grille
- blower
- Also called: fan, furnace fan, air handler fan
- airflow arrow
- Also called: direction arrow, air flow indicator, arrow on the filter
- central forced-air system
- Also called: furnace, central air conditioner, central AC, HVAC system, air handler
- MERV
- Also called: minimum efficiency reporting value, filter rating, filter efficiency
When to use a professional
Stop if you cannot find the filter slot. Stop if the cover has damage. Stop if the used filter is wet. Speak to an HVAC technician.
Also stop if the equipment does not start after you install the new filter. Do not open the cabinet of the equipment. The work behind that cover needs a trade qualification.
The EPA says that an HVAC technician must find the highest filter efficiency for your system. Ask the technician for that value. Record the value with the size of the filter. Then this page is sufficient for each replacement after the first.
Common questions
How often should I change my furnace filter?
ENERGY STAR says to inspect, clean or change the filter once a month, and to change it at least every three months. Heavy use months matter most, so a filter that looks clean in April can be grey by August. Households with pets, smokers or building work usually need a shorter interval.
Which way does the arrow on the air filter point?
The airflow arrow points in the direction the air moves, which is away from the return duct and towards the blower and the equipment. If you are unsure, note the direction of the old filter before you remove it. A filter fitted backwards restricts airflow.
What MERV rating should I use?
The EPA recommends at least MERV 13, or as high a rating as your system fan and filter slot can accommodate. MERV describes how well a filter captures particles between 0.3 and 10 microns. Higher is not automatically better: the EPA says an HVAC technician may be needed to determine the highest efficiency filter your particular system can use.
What size air filter do I need?
The size is printed on the cardboard frame of the filter already in the slot, and it is also in the documentation supplied with your equipment. This page does not print a size, because filter dimensions are specific to one model and a guessed size does not seal. Record the size once and the next purchase takes ten seconds.
Is a hot water heater filter the same thing?
No. This procedure covers the air filter in a central forced-air heating and cooling system only. Water filters, humidifier pads and range hood filters are separate items with their own intervals.
Does a dirty air filter actually cost money?
Yes. ENERGY STAR states that a dirty filter slows down air flow and makes the system work harder, which wastes energy, and that a dirty filter can increase energy costs and damage your equipment, leading to early failure.
Related procedures
- How to change the cabin air filter in a car when the air conditioning smells or barely blows
- How do I build a DIY box fan air purifier (Corsi-Rosenthal box) for wildfire smoke?
- How to clear a blocked condensate drain on a central air conditioner
- How to replace a thermostat and get the wires on the right terminals
- How to clean the outside AC unit / condenser coil before summer
- How to change the engine air filter in your car
- How to bleed a radiator that is cold at the top and warm at the bottom
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1Maintenance Checklist
- Tier 1Heat & Cool Efficiently
- Tier 1What is a MERV rating?
- Tier 1Guide to Air Cleaners in the Home
- Tier 1What kind of filter should I use in my home HVAC system to help protect my family?
Revision history
Current version 1 · updated 2026-07-28 · next review due 2027-07-28
- v1 · 2026-07-28First publication. Built end to end as the reference record for the build pipeline.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.