Choosing the right furnace filter and changing it when it is dirty is as important to your HVAC system as changing the oil is to your car. Each plays a critical role in keeping its system operating safely, efficiently and for a long time.

A dirty furnace filter loses its effectiveness, enabling potentially harmful particles to flow through your home. It also restricts airflow, which can damage your furnace and decrease its life span.

Making certain your furnace uses a clean filter that is suitable for your needs is not merely about keeping your furnace working efficiently. It’s also about creating good indoor air quality for your household.

Your health is important to the heating and cooling pros at Bell Mechanical Services. We've long been dedicated to enhancing indoor air quality in McKinney and Frisco. Here, we’ve answered common questions about HVAC filters, including that especially tricky question of what direction do you point a filter in your furnace or air conditioner?

How Often to Replace the Air Filter in a Furnace

Experts stress it's critical to replace dirty air filters in a furnace or air conditioner regularly. Soiled filters cause the system to worker harder than it should because it takes more energy to force air through the plugged-up filter.

Officials suggest examining your furnace filter monthly and replacing it if it’s dirty. You’ll know if your filter needs changing because it will filled with dirt or dust. Those who have pets that shed will likely want to replace their furnace air filter more often, because an effective air filter will trap pet hair circulating in a home.

Where Is the Air Filter in My Furnace?

In general, a furnace air filter is usually installed in the return air duct or blower compartment before the return air reaches the furnace. This makes sure air entering the system is filtered before it goes through the furnace components and is heated.

Depending on the furnace model, the filter may be positioned on the right, left, bottom or in some cases, within the furnace. It's usually housed within a slot, frame or cabinet for simple access and replacement. Always refer to your furnace's owner manual for information regarding filter location of your furnace.

Is My Furnace Filter Just a Type of Air Filter?

The straightforward answer is, yes. In HVAC, a furnace filter and an air filter or AC filter are effectively the same. While they might be called different things based on the current season— warm or chilly months—they are all filters that clean the air in your residence.

They each remove dust, allergens, bacteria and other particulates from the air that is drawn into the furnace and air conditioning system, ensuring the air circulating throughout your home is clean and safe.

What Are MERV Ratings and What Rating Is Best for Me?

Once you track down your old furnace filter and decide when it should be replaced, it’s time to choose a replacement. That means determining the level of filtration that you need. One method to do this is by choosing an appropriate MERV rating for your needs.

MERV is short for Minimum Efficiency Reporting Values. The MERV rating indicates the effectiveness of air filters at trapping airborne contaminants. The rating scale ranges from 1 to 20, with bigger numbers indicating a greater ability to filter small particles.

Experts say a filter with a MERV rating between 8 and 13 offers an ideal balance between having healthy indoor air quality without unnecessarily restricting airflow. However, people with some health conditions could need to purchase a filters with a higher MERV rating.

Where to Insert the Air Filter in a Furnace or Air Conditioner

Positioning an air filter in a furnace or air conditioner correctly is crucial for the efficient operation of the unit. Air filters are supposed to face a specific direction, indicated by an arrow written on the side of the filter frame. The filter should be put in with this arrow pointing at the furnace or air conditioner, which is the direction of the airflow. If you're doubtful about the airflow direction, it may be helpful to remember that air always moves from the return duct towards the heat or cooling source. Therefore, make certain the arrow points in the direction of the furnace or AC.

Many people have difficulty remembering which direction to install their air filter. To help remember, consider taking a quick picture with your cell phone after the filter has been properly installed by a professional. Or, you also could ask a technician to use a marker to write on the outside of your furnace which direction the filter should be installed. A perfect time to do this is during a scheduled furnace maintenance visit.

How to Replace Your Furnace Air Filter

Replacing the filter on your furnace or AC is an easy process. Here is a step-by-step rundown of how to remove a dirty air filter and swap it for a new one:

  1. Turn off your furnace: Be sure to turn off your furnace before starting up the process.
  2. Find the furnace filter: Typically, the filter is positioned inside the furnace or in the air return vent. Make a mental note or write down which direction the arrow points on the filter, because you’ll want the arrow on the new filter to point the same way.
  3. Remove the old filter: Be diligent not to knock out any dust or debris.
  4. Record the date: Write down the date you changed filters on the new filter's frame. This will help your family keep track of when it's time for the next change.
  5. Insert new filter: Put in the new filter with the arrow pointing at the furnace, which is the direction of airflow and should be the same direction the arrow pointed on the old filter you are replacing.
  6. Secure the filter: Make sure the new filter fits securely and close any latches or clips that secure it in the compartment.
  7. Turn on your furnace: Once the clean filter is properly secured, you can turn your furnace back on.

Can a Dirty Air Filter Cause Problems for a Furnace?

The simple answer is, yes, a dirty air filter can cause a furnace to stop working or shorten its lifespan. Changing your furnace or air conditioning filter is one of the simplest things you can do to keep your system working efficiently.