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When and How to Change Your Home's Furnace Air Filter

Changing your furnace filter is a quick and inexpensive DIY project that anyone can handle.

In this step-by-step guide, I will walk you through the entire process, from choosing the right filter size to properly installing it.

Quick Steps to Change Your Furnace Air Filter:

  1. Power Down: Turn off your furnace at the power switch.
  2. Locate Filter: Find the filter compartment (usually in the furnace, ductwork, or a return grille).
  3. Remove Old Filter: Carefully slide the old filter out, noting the airflow direction.
  4. Insert New Filter: Place the new filter with the airflow arrow pointing in the same direction as the old one.
  5. Close Compartment: Securely close the filter compartment door or cover.
  6. Power Up: Turn your furnace back on.

This quick guide summarizes the process—be sure to read the full article for detailed instructions and important safety considerations.

Table of Contents

When to Change Your Furnace Air Filter

While a general guideline is to change your filter every 1-3 months, several factors can influence how often you should replace it.

For most households in average conditions, changing the filter every 90 days is a good starting point. However, if you have pets that shed, live in a dusty environment, or have family members with allergies or respiratory sensitivities, you'll likely need to change your filter more frequently, potentially every 30-60 days.

Signs Your Furnace Air Filter Needs Replacement

A good way to gauge whether your filter needs replacing is to visually inspect it. Here are some telltale signs that your air filter is dirty and needs to be replaced:

  • Reduced airflow: Noticeably weaker airflow from your vents is a primary indicator of a clogged filter.
  • Increased dust accumulation: If you're dusting more frequently than usual, it could be a sign that your filter isn't effectively trapping dust particles.
  • Higher energy bills: A dirty filter restricts airflow, forcing your furnace to work harder and consume more energy.
  • Worsening allergies or respiratory issues: If allergy symptoms or respiratory problems seem to be flaring up, a dirty air filter could be contributing to the problem.
  • Visible dirt and debris: A quick visual inspection of the filter will reveal whether it's coated in dust, pet hair, and other particles. If it looks dirty, it's time for a change.

By paying attention to these signs and following the recommended guidelines, you can ensure that your furnace air filter is effectively cleaning the air and protecting your HVAC system.

Finding the Right Air Filter Size

Using the correct size air filter is essential for proper furnace function and efficient air filtration. An incorrectly sized filter can create gaps, allowing unfiltered air to bypass the filter and circulate through your home.

This not only reduces air quality but can also put extra strain on your HVAC system.

How to Determine the Correct Air Filter Size for Your Furnace

The easiest way is to check your existing filter. The dimensions (length x width x depth) are usually printed directly on the filter's cardboard frame. Common sizes include 16x20x1, 16x25x1, 20x25x1, and more.

Make a note of these numbers before purchasing a new filter.

If you can't locate the size on the old filter, consult your furnace owner's manual. The manual should specify the recommended filter size for your particular model.

Alternatively, you can also measure the filter slot in your furnace using a tape measure.

Types of Air Furnace Filters

Beyond size, air filters also come in various types and efficiency levels. The most common types include:

  • Fiberglass filters: These are the most basic and least expensive option, offering minimal filtration. They're suitable for trapping larger particles but are less effective at capturing smaller allergens and pollutants.
  • Pleated filters: These filters offer improved filtration compared to fiberglass, thanks to their pleated design, which increases surface area. They are a good mid-range option for most households.
  • HEPA filters (High-Efficiency Particulate Air): These filters offer the highest level of filtration, capturing up to 99.97% of airborne particles. They're ideal for individuals with allergies, asthma, or other respiratory conditions.

How Filter Efficiency is Measured

Filter efficiency is measured by the Minimum Efficiency Reporting Value (MERV) rating, which ranges from 1 to 16. Higher MERV ratings indicate better filtration.

However, it's important to choose a filter with a MERV rating compatible with your HVAC system, as very high MERV filters can restrict airflow and strain the system. Consult your furnace's documentation for the recommended MERV range.

Step-by-Step Guide to Changing Your Furnace Air Filter

Now that you have the right size replacement filter, let's walk through the simple process of changing it.

Step 1: Turn Off the Furnace

Locate your furnace's power switch, usually near the unit, and turn it off. This prevents the furnace from running while you're working with the filter.

Step 2: Locate the Air Filter Compartment

The filter compartment is typically located within the furnace itself, in the return air duct, or sometimes in a wall or ceiling return grille. Consult your furnace's manual if you're unsure. The compartment usually has a hinged door or a slot for easy access.

Step 3: Remove the Old Filter

  • Open the filter compartment and carefully slide out the old filter.
  • Pay attention to the direction of airflow, indicated by an arrow printed on the filter frame.
  • This will be important when installing the new filter.

Handle the old filter carefully to minimize dust release.

Step 4: Inspect the Old Filter

Take a moment to examine the old filter. A heavily soiled filter indicates that it was doing its job, but it also reinforces the importance of regular changes.

This is a good opportunity to assess your current filter change schedule and adjust it if necessary.

Step 5: Insert the New Filter

Slide the new filter into the compartment, ensuring the airflow arrow on the filter frame points in the same direction as the arrow on the old filter (typically towards the furnace). This ensures proper airflow.

Step 6: Close the Filter Compartment Securely

Make sure the compartment door or cover is properly latched or closed to prevent air leaks.

Step 7: Turn the Furnace Back On

Switch the power back on to your furnace. You've successfully changed your air filter!

By following these simple steps, you can easily change your furnace air filter and enjoy cleaner air and a more efficient HVAC system.

Tips for Choosing and Maintaining Your Furnace Air Filter

Beyond the basic steps of changing your filter, here are some additional tips for choosing the right filter and maintaining optimal air quality:

Understand Filter Types

As mentioned earlier, fiberglass filters offer basic filtration, pleated filters provide improved performance, and HEPA filters offer the highest level of filtration. Choose a filter type that balances your indoor air quality needs with your budget and HVAC system requirements.

Consider MERV Ratings

Remember that higher MERV ratings mean better filtration but can also restrict airflow. Consult your furnace documentation for the recommended MERV range. Using a filter with a MERV rating that’s too high can strain your system.

Set Reminders

It's easy to forget about changing your air filter. Set reminders on your phone or calendar to ensure you change the filter according to the recommended schedule. This will help maintain consistent air quality and prevent your furnace from overworking.

Check the Filter Monthly

Even if you're not due for a full filter change, it's a good idea to visually inspect the filter monthly, especially during periods of heavy use (like summer and winter). If it looks dirty, change it sooner than scheduled.

Don't Neglect Regular HVAC Maintenance

Changing your air filter is an important part of HVAC maintenance, but it's not the only task. Schedule professional HVAC inspections and tune-ups annually to ensure your entire system is running efficiently.

Frequently Asked Questions

What happens if I don’t change my furnace air filter?

Neglecting to change your furnace air filter can lead to a variety of problems, including:

  • reduced airflow
  • decreased indoor air quality
  • increased energy bills
  • and potential damage to your HVAC system

A clogged filter forces your furnace to work harder, leading to premature wear and tear and potentially costly repairs.

How often should I change my filter if I have pets?

If you have pets that shed, it's generally recommended to change your furnace air filter every 1-2 months. Pet dander can quickly clog a filter, reducing its effectiveness and impacting your indoor air quality.

Can I wash and reuse my furnace air filter?

While some filters are marketed as washable, most disposable filters are not designed for reuse. Washing a disposable filter can damage its fibers and reduce its effectiveness. It's generally recommended to replace your filter with a new one rather than attempting to wash it.

What does MERV rating mean?

MERV stands for Minimum Efficiency Reporting Value. It's a rating system that measures a filter's ability to trap airborne particles. Higher MERV ratings indicate better filtration.

How do I know if I have the right size filter?

The easiest way to determine the correct filter size is to check the dimensions printed on your existing filter. If you can't find the size on the old filter, consult your furnace's owner's manual or measure the filter slot in your furnace.

What if my furnace filter is a non-standard size?

If you have a non-standard sized filter, you might need to order a custom-sized filter or contact an HVAC professional for assistance. They can help you find the correct filter or suggest alternative solutions.

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