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

A dirty furnace filter loses its effectiveness, allowing potentially harmful particles to move through your home. It also slows airflow, which can damage your furnace and shorten 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 healthy indoor air quality for your household.

The health of your family is important to the HVAC pros at GV Heating & Air. We've long worked with an eye on improving indoor air quality in Crystal and Twin Cities. Here, we’ve answered frequent questions about HVAC filters, including that very 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

It's critical to replace dirty air filters in a furnace or air conditioner routinely. Dirt-clogged filters cause the system to worker harder than it should because it takes extra effort to pull air through the plugged-up filter.

Officials recommend inspecting your furnace filter every 30 days and replacing it if it’s dirty. You’ll know if your filter needs changing because it will be gray or black from dirt or dust. Those who have pets that shed will likely want to replace their furnace air filter more often, because a good air filter will trap pet hair circulating in a home.

How to Find the Furnace's Air Filter

In general, a furnace air filter is usually installed in the return air duct or blower compartment before the return air gets to the furnace. This ensures air flowing into the system is filtered before it goes through the furnace components and is heated.

Depending on the furnace brand, the filter may be found on the right, left, bottom or in some cases, on the inside of the furnace. It's usually housed within a slot, frame or cabinet for easy access and replacement. Always refer to your furnace's owner manual for facts 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 people might refer to them differently based on the current season— warm or chilly months—they are all filters that clean the air in your home.

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 Is the MERV Rating System and What Rating Is Best for Me?

Once you track down your old furnace filter and determine when it should be substituted for a clean one, it’s time to choose a replacement. That means deciding on the level of filtration that you need. One approach to this is by choosing an appropriate MERV rating for your needs.

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

Experts say a filter with a MERV rating between 8 and 13 offers a good balance between having adequate indoor air quality without unnecessarily restricting airflow. However, people with specific health conditions might need to purchase a filters with a higher MERV rating.

Where to Insert the Air Filter in a Furnace or Air Conditioning System

Installing an air filter in a furnace or air conditioner the proper way is necessary for the efficient operation of the system. Air filters have a specific direction, indicated by an arrow written on the side of the filter frame. The filter should be installed with this arrow pointing toward the furnace or air conditioning unit, which is the direction of the airflow. If you're not sure about the airflow direction, try to remember that air always moves from the return duct to the heat or cooling source. Therefore, make sure the arrow points at the furnace or air conditioning unit.

Many people have difficulty remembering which direction to face their air filter. To help remember, consider snapping a quick photo with your cellular phone after the filter has been accurately 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 handy time to ask about this is during a routine furnace maintenance appointment.

Changing Your Furnace's Air Filter

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

  1. Turn off your furnace: Be sure to switch off your furnace before starting the process.
  2. Locate the furnace filter: Typically, the filter is positioned in the furnace or in the air return vent. Make note of which direction the arrow points on the filter, because you’ll want the arrow on the new filter to point the same way.
  3. Slide out the old filter: Be careful not to knock out any dust or particles.
  4. Note the date: Write down the date of replacement on the new filter's frame. This will help you keep track of when it's time for you to change it again.
  5. Insert new filter: Put in the new filter with the arrow pointing toward 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 nicely and close any latches or clips that hold it in place.
  7. Turn on your furnace: Once the new filter is safely installed, you can turn your furnace back on.

Can a Dirty Air Filter Damage My Furnace?

The shortest answer is, yes, a dirty air filter can cause a furnace to cease working or limit its lifespan. Changing your furnace or AC filter is one of the best things you can do to keep your system operating correctly.