Selecting the proper 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 crucial function in keeping its system running safely, efficiently and for a long time.

An overused furnace filter loses its effectiveness, allowing potentially harmful particles to flow through your home. It also limits airflow, which can damage your furnace and decrease its life span.

Making certain your furnace uses a clean filter that is ideal for your needs is not merely about keeping your furnace working efficiently. It’s also about providing healthy indoor air quality for your residence.

Your health is important to the heating and cooling professionals at Gilray Heating and Cooling. We've long focused on enhancing indoor air quality in Wausau. 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?

When to Replace the Air Filter in Your 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 effort to move air through the plugged-up filter.

Officials recommend checking your furnace filter monthly and replacing it if it’s dirty. You’ll know if the filter needs to be changed because it will filled with dirt or dust. People who have pets will very likely have 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 located in the return air duct or blower compartment before the return air gets to the furnace. This is so air entering the system is filtered before it goes through the furnace components and is heated.

Depending on the furnace brand, the filter may be located on the right, left, bottom or in some cases, inside 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 details concerning filter location of your furnace.

Is a Furnace Filter the Same as an Air Filter?

The simple answer is, yes. In HVAC, a furnace filter and an air filter or air conditioning filter are basically identical. While people might refer to them differently based on the current season— hot or cold—they are all filters that clean the air in your HVAC system.

They each eliminate dust, allergens, bacteria and other airborne debris 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 Should I Have?

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

MERV is an abbreviation 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 the power to filter tinier particles.

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

Where to Insert the Air Filter in a Furnace or AC Unit

Positioning an air filter in a furnace or air conditioner properly is crucial for the efficient operation of the unit. Air filters are supposed to face a particular 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 at the furnace or air conditioning unit, which is the direction of the airflow. If you're doubtful 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 in the direction of the furnace or air conditioner.

Many people struggle with which direction to face 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 be installed. A perfect time to ask about this is during a regular furnace maintenance call.

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 rundown of how to remove a dirty air filter and swap it for a new one:

  1. Turn off your furnace: Make sure to shut off your furnace before starting up the process.
  2. Locate 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 clean filter to point similarly.
  3. Remove the old filter: Be careful not to knock out any dust or dirt.
  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 you to change it again.
  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 securely and close any latches or clips that secure it in the compartment.
  7. Turn on your furnace: Once the clean filter is completely 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 decrease its lifespan. Changing your furnace or AC filter is one of the easiest things you can do to keep your system working efficiently.