Choosing the proper 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, allowing potentially harmful particles to move through your home. It also limits airflow, which can damage your furnace and decrease its life span.

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

The quality of the air your family breathes is important to the heating and cooling specialists at Fairfield Heating & Cooling. We've long focused on bettering indoor air quality in Lancaster. 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 important to replace dirty air filters in a furnace or air conditioner routinely. Soiled filters cause the system to worker harder than it should because it takes extra work to pull air through the plugged-up filter.

Officials advise examining your furnace filter monthly and replacing it if it’s dirty. You’ll know if it is dirty because it will be gray or black from dirt or dust. People who have dogs and cats will very likely need 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 commonly located in the return air duct or blower compartment before the return air goes back into 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 type of furnace, the filter may be positioned on the right, left, bottom or in some cases, on the inside of the furnace. It's typically housed inside of a slot, frame or cabinet for simple access and replacement. Always refer to your furnace's owner manual for details regarding filter location of your furnace.

Are Air Filters and Furnace Filters the Same Thing?

The straightforward answer is, yes. In HVAC, a furnace filter and an air filter or air conditioner filter are effectively the same. While people might refer to them differently based on the current season— summer or winter—they are all filters that clean the air in your home.

They each remove dust, allergens, bacteria and other particulates from the air that is drawn into the furnace and air conditioning system, making certain the air flowing through your home is clean and safe.

What Are MERV Ratings and What Rating Is Best for Me?

Once you find your old furnace filter and figure out when it should be substituted for a clean one, it’s time to pick a replacement. That means determining the level of filtration that you need. One approach to this is by picking 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 small particles.

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

How to Place the Air Filter in a Furnace or Air Conditioning System

Installing an air filter in a furnace or air conditioner correctly is crucial for the efficient operation of the heating or cooling system. Air filters are designed to be installed in a certain direction, indicated by an arrow located on the side of the filter frame. The filter should be put in with this arrow pointing in the direction of the furnace or air conditioner, which is the direction of the airflow. If you're unsure about the airflow direction, try to remember that air always moves from the return duct and then to the heat or cooling source. Therefore, make certain the arrow points toward the furnace or air conditioner.

Many people have difficulty remembering which direction to point an 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 be installed. A handy time to inquire about this is during a scheduled furnace maintenance visit.

Changing Your Furnace's Air Filter

Changing the filter on your furnace or air conditioning system is an easy process. Here is a step-by-step breakdown of how to remove a dirty air filter and swap it for a new one:

  1. Turn off your furnace: Make sure to switch off your furnace before beginning the process.
  2. Locate the furnace filter: Typically, the filter is located within 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 replacement filter to point similarly.
  3. Take out the old filter: Be diligent not to knock out any dust or dirt.
  4. Note the date: Write down the date of replacement 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 toward the furnace, which is the direction of airflow and should be the same direction the arrow pointed on your last filter.
  6. Secure the filter: Make sure the new filter fits nicely and close any latches or clips that secure it in the compartment.
  7. Turn on your furnace: Once the clean filter is properly installed, you can turn your furnace back on.

Can a Dirty Air Filter Damage My Furnace?

The simple 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 best things you can do to keep your system running efficiently.