How to Change a Furnace Filter: The Easiest Home Maintenance Task
How to Change a Furnace Filter: The Easiest Home Maintenance Task
Changing your furnace filter is the single most impactful maintenance task you can do for your HVAC system, and it takes less than five minutes. A clean filter improves air quality, reduces energy consumption, extends the life of your furnace and air conditioner, and prevents expensive repairs. A dirty filter, on the other hand, restricts airflow, forces the system to work harder, raises your energy bill, and can freeze the evaporator coil or overheat the heat exchanger.
Despite all that, surveys show that more than half of homeowners either do not change their filter regularly or do not know where it is. This guide fixes that.
Turn off your HVAC system before removing or inserting a filter. This prevents unfiltered air from being pulled through the system.
Quick Overview
| Detail | Info |
|---|---|
| Difficulty | Beginner (easiest task in this guide series) |
| Time | 2–5 minutes |
| Cost | $5–$30 per filter |
| Tools needed | None |
| Frequency | Every 1–3 months |
Step 1: Find Your Filter
The filter is located somewhere between the return air duct and the furnace/air handler. Common locations:
| Location | Description |
|---|---|
| Return air grille | On a wall or ceiling — the large vent with no airflow when the system is on. Remove the grille (usually secured by clips or screws) to access the filter. |
| Furnace cabinet | Inside the blower compartment of the furnace. Look for a slot where the filter slides in, usually at the bottom or side of the unit. |
| Air handler closet | If your system has a separate air handler (common with heat pumps), the filter may be inside the air handler unit. |
If you have never found your filter before, check all three locations. Your system may have more than one filter.
Step 2: Check the Current Filter
- Turn off the HVAC system using the thermostat or the system power switch.
- Slide the old filter out. Note which direction the airflow arrow points — this is critical for installing the new filter correctly.
- Inspect the filter. Hold it up to a light:
- If you can see light through it, it has some life left (but check the replacement schedule below).
- If it is grey, dark, or coated with dust and debris, it needs to be replaced now.
- If it is damp or shows signs of mold, replace it immediately and investigate the moisture source.
Step 3: Buy the Right Replacement
Filter Size
The size is printed on the frame of the existing filter (for example: 16x25x1, 20x20x1, or 16x25x4). Write it down or take a photo. Filter sizes must match exactly — a filter that does not fit properly allows unfiltered air to bypass.
Filter Type and MERV Rating
MERV (Minimum Efficiency Reporting Value) rates how effectively a filter captures particles:
| MERV Rating | Captures | Best For |
|---|---|---|
| 1–4 | Pollen, dust mites, carpet fibers | Minimal filtration (builder-grade fiberglass) |
| 5–8 | Mold spores, pet dander, dust | Standard home use — good balance of filtration and airflow |
| 9–12 | Fine dust, legionella, humidifier dust | Better air quality, homes with allergies or pets |
| 13–16 | Bacteria, tobacco smoke, virus carriers | Hospital-grade — may restrict airflow in residential systems |
Recommendation for most homes: MERV 8–11. This range captures the particles that matter for indoor air quality without restricting airflow enough to strain your system. Higher is not always better — a MERV 16 filter in a system designed for MERV 8 can reduce airflow, increase energy costs, and damage the blower motor.
Filter Types
| Type | MERV Range | Cost | Change Frequency |
|---|---|---|---|
| Fiberglass (flat panel) | 1–4 | $1–$3 | Every 30 days |
| Pleated | 5–12 | $5–$15 | Every 60–90 days |
| Deep pleated (4–5 inch) | 8–16 | $15–$30 | Every 6–12 months |
| Washable/reusable | 1–4 | $30–$80 | Wash monthly, replace every 5 years |
Pleated filters are the best value for most homes — better filtration than fiberglass, reasonable cost, and a two-to-three month replacement interval.
Step 4: Install the New Filter
- Check the airflow arrow on the new filter. The arrow must point toward the furnace/air handler (in the direction of airflow). If the filter is in a return grille, the arrow points toward the wall (into the duct).
- Slide the new filter in. It should fit snugly without bending or buckling.
- Close the access panel or grille.
- Turn the HVAC system back on.
- Write the installation date on the filter frame with a permanent marker. This makes it easy to know when it was last changed.
Replacement Schedule
| Situation | Frequency |
|---|---|
| Standard home, no pets | Every 90 days |
| Home with one pet | Every 60 days |
| Home with multiple pets or allergies | Every 30–45 days |
| Summer (AC running constantly) | Every 30 days |
| Vacation home or light use | Every 6–12 months (check before each use) |
Set a recurring reminder on your phone or calendar. The few minutes it takes to change a filter saves hundreds of dollars in energy costs and prevents thousands in potential HVAC repairs.
What Happens When You Ignore the Filter
The consequences of a neglected filter escalate:
- Reduced airflow — rooms heat or cool unevenly.
- Higher energy bills — the system runs longer to compensate (10–15 percent increase in energy use).
- Frozen evaporator coil — restricted airflow drops the coil temperature below freezing, forming ice. The system stops cooling and can damage the compressor ($1,000+ repair).
- Overheated heat exchanger — in heating mode, restricted airflow causes the furnace to overheat and shut down on safety. Repeated overheating can crack the heat exchanger ($1,500–$3,000 repair), which can also leak carbon monoxide.
- Premature system failure — chronic airflow restriction shortens the lifespan of your entire HVAC system.
When to Call an HVAC Professional
- The filter is dirty and the system is not producing adequate heat or cooling despite a fresh filter (may indicate a deeper problem)
- You find the filter is damp or moldy (indicates condensation or ductwork issue)
- You do not know where your filter is and cannot find it in any of the common locations
- Your system uses a non-standard filter size or configuration
For a comprehensive guide to your home’s mechanical systems, see our home plumbing guide. To plan seasonal maintenance tasks, check our spring maintenance checklist and winterization guide. For understanding the full range of home maintenance costs, see our home repair cost guide.
Frequently Asked Questions
Can I run the HVAC system without a filter temporarily? You can for a very short period (a few hours), but it is not recommended. Unfiltered air carries dust and debris directly into the system, coating the evaporator coil and blower motor.
Are expensive filters worth it? For most homes, a mid-range pleated filter (MERV 8–11, $5–$15) is the best value. The cheapest fiberglass filters do not capture enough particles. The most expensive filters may restrict airflow unless your system is designed for them.
Can a dirty filter make me sick? A severely clogged filter reduces air quality by recirculating dust, allergens, and potentially mold spores. People with asthma or allergies are most affected. Regular replacement is a health investment as well as a maintenance one.
This article is for informational purposes only. Always verify compatibility with your specific HVAC system. Consult a licensed HVAC professional for system-specific questions.