Picking out the correct 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 running 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 reduce its life span.

Making certain your furnace uses a clean filter that is appropriate for your needs is not just about keeping your furnace working efficiently. It’s also about creating excellent indoor air quality for your residence.

Your health is important to the heating pros at Franklin's Heating & Air Conditioning, Inc. We've long worked with an eye on bettering indoor air quality in Oxford. Here, we’ve answered frequent 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

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

Officials recommend examining your furnace filter every 30 days and replacing it if it’s dirty. You’ll know if it is dirty because it will filled with dirt or dust. People who have pets that shed will likely need to replace their furnace air filter more often, because a quality air filter will trap pet hair circulating in a home.

Locating Your Furnace's Air Filter

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

Depending on the furnace brand, the filter may be positioned on the right, left, bottom or in some cases, inside the furnace. It's typically housed within a slot, frame or cabinet for convenient access and replacement. Always refer to your furnace's owner manual for information about filter location of the furnace in your home.

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 air conditioning filter are essentially 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 home.

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

What Are MERV Ratings and What MERV Rating Do I Need?

Once you locate your old furnace filter and decide 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 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 measures 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 small 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 could need to purchase a filters with a higher MERV rating.

How to Place the Air Filter in a Furnace or Air Conditioner

Positioning an air filter in a furnace or air conditioner correctly is necessary for the efficient operation of the system. Air filters are supposed to face a specific direction, indicated by an arrow located on the side of the filter frame. The filter should be put in with this arrow pointing at the furnace or AC, 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 towards the heat or cooling source. Therefore, make sure the arrow points at the furnace or air conditioning unit.

Many people struggle with which direction to face their air filter. To help remember, consider snapping a quick photo with your mobile phone after the filter has been correctly 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 great time to ask about this is during a regular furnace maintenance appointment.

Changing Your Furnace's Air Filter

Changing 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 shut off your furnace before starting the process.
  2. Locate 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 clean filter to point similarly.
  3. Remove the old filter: Be careful not to knock out any dust or particles.
  4. Note the date: Write down the date you replaced the filter 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 dirty filter you just removed.
  6. Secure the filter: Make sure the new filter fits nicely and close any latches or clips that hold it in the unit.
  7. Turn on your furnace: Once the replacement filter is completely in place, you can turn your furnace back on.

Will a Dirty Air Filter Cause a Furnace Not to Work?

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