Selecting the ideal furnace filter and changing it when it gets dirty is as important to your HVAC system as changing the oil is to your car. Each plays a vital part in keeping its system running safely, efficiently and for a long time.

A dirty furnace filter loses its effectiveness, enabling potentially harmful particles to circulate 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 good indoor air quality for your home.

The quality of the air your family breathes is important to the heating pros at Lanz Furnace and Fireplace. We've long focused on bettering indoor air quality in Monroe. 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?

When Should I Replace My Furnace Air Filter?

It's vital 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 work to move air through the plugged-up filter.

Officials suggest checking your furnace filter every month and replacing it if it’s dirty. You’ll know if it is dirty because it will be gray or black from dirt or dust. Those who have pets that shed will probably want to replace their furnace air filter more often, because an effective 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 entering the system is filtered before it passes through the furnace components and is heated.

Depending on the type of furnace, the filter may be located on the right, left, bottom or in some cases, on the inside of the furnace. It's generally housed inside of a slot, frame or cabinet for simple access and replacement. Always refer to your furnace's owner manual for information concerning filter location of your particular brand and model of furnace.

Is a Furnace Filter the Same as an Air Filter?

The easy answer is, yes. In HVAC, a furnace filter and an air filter or AC filter are essentially identical. 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 HVAC system.

They each get rid of dust, allergens, bacteria and other particulates from the air that is drawn into the furnace and air conditioning system, making sure the air distributed throughout your home is clean and safe.

What Is the MERV Rating System and What MERV Rating Do I Need?

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

MERV is short for Minimum Efficiency Reporting Values. The MERV rating measures the effectiveness of air filters at trapping airborne molecules. The rating scale ranges from 1 to 20, with higher 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 adequate indoor air quality without overly restricting airflow. However, people with specific health conditions could need to purchase a filters with a higher MERV rating.

Which Way to Put the Air Filter in a Furnace or AC Unit

Putting an air filter in a furnace or air conditioner correctly is important for the efficient operation of the heating or cooling system. Air filters are supposed to face a certain direction, indicated by an arrow printed on the side of the filter frame. The filter should be placed in the unit with this arrow pointing in the direction of the furnace or air conditioning unit, which is the direction of the airflow. If you're not sure about the airflow direction, remember that air always moves from the return duct and then to the heat or cooling source. Therefore, make sure the arrow points at the furnace or air conditioner.

Many people struggle with which direction to install an air filter. To help remember, consider taking a picture with your cell 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 go. A perfect time to do this is during a regular furnace maintenance visit.

How to Change a Furnace Air Filter

Replacing the filter on your furnace or air conditioner is a simple process. Here is a step-by-step breakdown 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 beginning the process.
  2. Look for the furnace filter: Typically, the filter is found within 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 clean filter to point similarly.
  3. Slide out the old filter: Be mindful not to knock out any dust or particles.
  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. Put in 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 dirty filter you just removed.
  6. Secure the filter: Make sure the new filter fits securely and close any latches or clips that hold it in the compartment.
  7. Turn on your furnace: Once the replacement filter is properly in place, you can turn your furnace back on.

Will a Dirty Air Filter Damage My Furnace?

The short answer is, yes, a dirty air filter can cause a furnace to stop working or reduce its lifespan. Changing your furnace or air conditioning filter is one of the easiest things you can do to keep your system working correctly.