Choosing the ideal 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 function in keeping its system running 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 reduce its life span.

Ensuring your furnace uses a clean filter that is appropriate for your needs is not merely about keeping your furnace operating efficiently. It’s also about providing excellent indoor air quality for your residence.

The health of your family is important to the HVAC specialists at Smyth Air Conditioning. We've long focused on enhancing indoor air quality in Lake Worth. 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. Dirty filters cause the system to worker harder than it should because it takes more energy 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 the filter needs to be changed because it will coated with dirt or dust. People who have pets that shed will probably need to replace their furnace air filter more often, because a good 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 normally located in the return air duct or blower compartment before the return air goes back into the furnace. This is so air being pulled into the system is filtered before it goes through the furnace components and is heated.

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

Is a Furnace Filter the Same as an Air Filter?

The straightforward answer is, yes. In HVAC, a furnace filter and an air filter or air conditioning filter are essentially identical. While people may call them different things based on the current season— summer or winter—they are all filters that clean the air in your HVAC system.

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 circulating throughout your home is clean and safe.

What Is a MERV Rating and What MERV Rating Do I Need?

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

MERV stands 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 bigger numbers indicating enhanced capabilities to filter smaller particles.

Experts say a filter with a MERV rating between 8 and 13 offers an appropriate balance between having adequate indoor air quality without unnecessarily restricting airflow. However, people with certain health conditions might need a a higher MERV rating.

Which Way to Put the Air Filter in a Furnace or Air Conditioner

Putting an air filter in a furnace or air conditioner properly is necessary for the efficient operation of the unit. Air filters are designed to be installed in a specific direction, indicated by an arrow printed 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 not sure about the airflow direction, remember that air always moves from the return duct and then to the heat or cooling source. Therefore, be sure that the arrow points toward the furnace or air conditioning unit.

Many people have difficulty remembering which direction to point an air filter. To help remember, consider snapping a quick photo with your cellular 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 perfect time to inquire about this is during a scheduled furnace maintenance visit.

How to Change a Furnace Air Filter

Replacing the filter on your furnace or air conditioning system is a quick and easy process. Here is a step-by-step list of how to remove a dirty air filter and replace it with a new one:

  1. 1. Turn off your furnace: Make a point to shut off your furnace before starting the process.
  2. Look for the furnace filter: Typically, the filter is found inside the furnace or in the air return vent. Take note of which direction the arrow points on the filter, because you’ll want the arrow on the replacement filter to point similarly.
  3. Take out the old filter: Be diligent not to knock out any dust or particles.
  4. Document 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 the next change.
  5. Slide in new filter: Put in the new filter with the arrow pointing in the direction of 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 correctly and close any latches or clips that hold it in the compartment.
  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 shortest answer is, yes, a dirty air filter can cause a furnace to cease working or limit its lifespan. Changing your furnace or air conditioning filter is one of the simplest things you can do to keep your system running efficiently.