Guide: How to Change HVAC Filters

Difficulty: Easy Time Required: 10–15 minutes

Changing your HVAC filter is the single most important maintenance task for your heating and cooling system. A dirty filter makes your system work harder, increases energy bills, reduces air quality, and can lead to expensive repairs. This simple task takes 10 minutes every 1–3 months and can extend your HVAC system's life by years. Even if you've never done home maintenance before, you can handle this one.

What You'll Need

Materials:

• New HVAC filter in the correct size (check current filter for dimensions)
• Phone or paper to note the filter size
• Stepladder or step stool (if filter location is high)
• Flashlight (if filter area is dark)

Prerequisites:

• Located your HVAC system or air return vent
• 10 minutes of time
• No special skills or tools required
• Basic ability to read numbers on the filter frame

Step-by-Step Instructions

Step 1: Locate your HVAC filter

The filter is usually in one of three places: inside the air return vent (a large grill on your wall or ceiling), at the HVAC unit itself (basement, attic, or utility closet), or in the return air duct near the furnace. Walk around your home looking for large vents—the return vent will be bigger than regular heating/cooling vents and won't have adjustable slats.

Step 2: Note the filter size before removing it

Look at the cardboard frame of your current filter. You'll see three numbers like 16x20x1 or 20x25x4 printed on the side. These measurements are length × width × thickness in inches. Take a photo of these numbers or write them down—you need this exact size when buying replacement filters.

Step 3: Turn off your HVAC system (optional but recommended)

Use your thermostat to turn the system to "off" or switch the fan setting from "auto" to "off." This isn't mandatory for safety, but it prevents the system from running while the filter is out and keeps dust from being pulled through the unit. You only need it off for 5–10 minutes.

Step 4: Remove the old filter

Open the air return vent cover (if applicable) or access panel. Slide or pull out the old filter—it should slide out easily. Pay attention to which direction the arrows on the frame are pointing. These arrows show airflow direction and must point the same way when you install the new filter.

Step 5: Insert the new filter in the correct direction

Look at the new filter's cardboard frame—you'll see arrows and text saying "AIR FLOW." These arrows must point toward the furnace/HVAC unit and away from the room. The air flows from your house, through the filter, and into the system. Slide the new filter into the same slot where you removed the old one, arrows pointing the correct direction.

Step 6: Close the cover and turn the system back on

Close the air return vent cover or access panel securely. Return to your thermostat and turn the system back to your desired setting. The system should run normally. Set a reminder on your phone or calendar to check and replace the filter again in 1–3 months depending on your filter type and household conditions.

Common Mistakes to Avoid

• Installing the filter backwards: The arrows on the filter frame must point toward the HVAC unit, not toward the room. Installing it backwards reduces efficiency and lets dust through. If you're unsure, remember: air flows from your living space, through the filter, into the system.
• Buying the wrong size filter: A filter that's too small allows unfiltered air around the edges. Too large won't fit. Always write down or photograph the exact three-number size from your old filter. Don't guess or estimate—precise sizing matters for proper fit and function.
• Waiting too long between changes: "Change every 90 days" is a minimum guideline. If you have pets, allergies, or lots of dust, change monthly. If you have multiple pets or live in a dusty area, change every 2–3 weeks. Check it monthly by holding it up to light—if you can't see through it clearly, change it.
• Leaving the system running without a filter: Never run your HVAC system without a filter, even briefly. Unfiltered air carries dust directly into your system's internal components, causing damage that requires expensive professional repairs. If your filter is extremely dirty, change it immediately rather than waiting.
• Buying the cheapest filter without considering needs: Basic fiberglass filters ($1–3) only catch large particles. If you have allergies, asthma, or pets, spend $8–15 on pleated filters with MERV 8–11 ratings. These catch smaller particles and improve air quality significantly while still allowing proper airflow.

Pro Tips

• Buy filters in bulk online: Amazon, Home Depot, and FilterBuy sell multipacks of 6–12 filters at significant discounts. If you need 16x20x1 filters, buy a year's supply for $40–60 instead of paying $8–15 per filter at hardware stores.
• Set up subscription delivery: Many filter companies offer automatic delivery every 1–3 months. Subscribe and save 5–15% while ensuring you never forget to change your filter. Cancel anytime if your needs change.
• Check filter monthly, change when needed: Don't blindly follow 90-day recommendations. Pull out your filter once per month and hold it up to a bright light. If you can't see light through it clearly, it's time to change. Some households need monthly changes; others can go 3 months.
• Mark the filter with installation date: Use a permanent marker to write the installation date on the filter's cardboard frame: "Installed: Jan 28, 2026." This eliminates guessing about when you last changed it.
• Keep spare filters near the HVAC system: Store 2–3 extra filters in a closet near your HVAC unit or air return vent. When it's time to change the filter, you have a replacement immediately available instead of needing to make a trip to the store first.

Related Skills

• How to Make Simple Home Repairs
• How to Create a Cleaning Schedule
• How to Check Your Car's Fluids
• How to Build a Simple Emergency Kit