Choosing 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 critical part in keeping its system working safely, efficiently and for a long time.

A clogged furnace filter loses its effectiveness, permitting 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 ideal for your needs is not merely about keeping your furnace operating efficiently. It’s also about providing healthy indoor air quality for your household.

Your health is important to the heating and cooling pros at Haselhoff Air Solutions. We've long focused on bettering indoor air quality in Ames. Here, we’ve answered frequent questions about HVAC filters, including that particularly 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 is critical to replace dirty air filters in a furnace or air conditioner periodically. Dirty filters cause the system to worker harder than it should because it takes extra effort to move air through the plugged-up filter.

Officials suggest examining your furnace filter every 30 days 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 dogs and cats will very likely need to replace their furnace air filter more often, because a quality 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 usually located in the return air duct or blower compartment before the return air gets to the furnace. This ensures air being pulled into 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 usually housed in a slot, frame or cabinet for convenient 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 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 conditioner filter are effectively the same thing. While people may call them different things based on the current season— hot or cold—they are all filters that clean the air in your residence.

They each eliminate dust, allergens, bacteria and other airborne debris 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 Is a MERV Rating and What Rating Is Best for Me?

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

MERV is an abbreviation 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 greater 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 overly restricting airflow. However, people with some health conditions might need to use a filter with a higher MERV rating.

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

Putting an air filter in a furnace or air conditioner properly is important for the efficient operation of the system. Air filters are supposed to face a particular direction, indicated by an arrow located on the side of the filter frame. The filter should be put in with this arrow pointing toward 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 to the heat or cooling source. Therefore, be sure that the arrow points at 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 cell 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 do this is during a regular furnace maintenance visit.

Changing Your Furnace's Air Filter

Switching out the filter on your furnace or AC is a simple process. Here is a step-by-step list of how to take out a dirty air filter and exchange it for a new one:

  1. Turn off your furnace: Make a point to turn off your furnace before beginning the process.
  2. Look for the furnace filter: Typically, the filter is positioned in 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. Remove the old filter: Be diligent not to knock out any dust or debris.
  4. Record the date: Write down the date of replacement on the new filter's frame. This will make it easier to keep track of when it's time for another replacement.
  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 old filter you are replacing.
  6. Secure the filter: Make sure the new filter fits correctly and close any latches or clips that secure it in the compartment.
  7. Turn on your furnace: Once the new filter is completely installed, 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 quit working or decrease its lifespan. Changing your furnace or AC filter is one of the best things you can do to keep your system working correctly.