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

A clogged furnace filter loses its effectiveness, enabling potentially harmful particles to flow through your home. It also restricts airflow, which can damage your furnace and shorten its life span.

Making sure your furnace uses a clean filter that is appropriate for your needs is not only about keeping your furnace operating efficiently. It’s also about providing good indoor air quality for your residence.

The quality of the air your family breathes is important to the heating and cooling professionals at Halverson Brothers Inc. We've long been dedicated to bettering indoor air quality in Menomonie and western Wisconsin. 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?

When to Replace the Air Filter in Your Furnace

Experts stress it's critical to replace dirty air filters in a furnace or air conditioner periodically. 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 checking your furnace filter every month and replacing it if it’s dirty. You’ll know if your filter needs changing because it will coated with dirt or dust. Homeowners who have pets will probably want to replace their furnace air filter more often, because an effective 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 entering the system is filtered before it moves 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, within the furnace. It's generally housed inside of a slot, frame or cabinet for easy access and replacement. Always refer to your furnace's owner manual for information regarding filter location of your particular brand and model of 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 essentially the same. 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 remove dust, allergens, bacteria and other airborne debris from the air that is drawn into the furnace and air conditioning system, ensuring the air flowing through 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 decide when it should be replaced, it’s time to select a replacement. That means deciding on the level of filtration that you need. One method to do this is by picking 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 particles. 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 an ideal balance between having adequate indoor air quality without needlessly restricting airflow. However, people with certain health conditions may need to use a filter with a higher MERV rating.

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

Positioning an air filter in a furnace or air conditioner properly is crucial for the efficient operation of the heating or cooling system. 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 AC, 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 towards the heat or cooling source. Therefore, be sure that the arrow points toward the furnace or AC.

Many people have difficulty remembering which direction to face their system's 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 great time to inquire about this is during a regular furnace maintenance call.

Changing Your Furnace's Air Filter

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

  1. Turn off your furnace: Make sure to shut off your furnace before starting the process.
  2. Look for the furnace filter: Typically, the filter is located inside 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 diligent not to knock out any dust or dirt.
  4. Record the date: Write down the date you replaced the filter on the new filter's frame. This will make it easier to keep track of when it's time for you to change it again.
  5. Put in new filter: Put in the new filter with the arrow pointing at 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 lock it in the compartment.
  7. Turn on your furnace: Once the clean filter is safely installed, you can turn your furnace back on.

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

The short answer is, yes, a dirty air filter can cause a furnace to quit working or limit its lifespan. Changing your furnace or AC filter is one of the easiest things you can do to keep your system working efficiently.