Picking out the correct 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 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 circulate through your home. It also slows airflow, which can damage your furnace and shorten its life span.

Making certain 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 good indoor air quality for your home.

Your health is important to the heating specialists at Strine's. We've long focused on bettering indoor air quality in York. 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?

How Often to Replace the Air Filter in a Furnace

It is important to replace dirty air filters in a furnace or air conditioner routinely. Dirty filters cause the system to worker harder than it should because it takes extra work to force air through the plugged-up filter.

Officials advise inspecting 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. Homeowners who have pets will very likely have to replace their furnace air filter more often, because a quality 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 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 passes 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 typically housed inside of a slot, frame or cabinet for simple access and replacement. Always refer to your furnace's owner manual for details about filter location of your furnace.

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 the same thing. While people might refer to them differently based on the current season— warm or chilly months—they are all filters that clean the air in your home.

They each eliminate dust, allergens, bacteria and other contaminants from the air that is drawn into the furnace and air conditioning system, making certain 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 decide when it should be changed, it’s time to select a replacement. That means picking the level of filtration that you need. One way to do that is by picking 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 particles. The rating scale ranges from 1 to 20, with bigger numbers indicating the power to filter small particles.

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

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

Putting an air filter in a furnace or air conditioner correctly is necessary for the efficient operation of the heating or cooling 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 installed with this arrow pointing in the direction of the furnace or air conditioner, which is the direction of the airflow. If you're not sure about the airflow direction, it may be helpful to remember that air always moves from the return duct to the heat or cooling source. Therefore, make certain the arrow points at the furnace or air conditioning unit.

Many people are confused by which direction to face an air filter. To help remember, consider taking a quick picture with your mobile phone after the filter has been properly 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 point. A handy time to do this is during a scheduled furnace maintenance appointment.

How to Replace Your Furnace Air Filter

Changing 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 retreive a dirty air filter and replace it with a new one:

  1. Turn off your furnace: Make a point to shut off your furnace before beginning the process.
  2. Look for the furnace filter: Typically, the filter is found within 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 new filter to point similarly.
  3. Slide out the old filter: Be diligent not to knock out any dust or dirt.
  4. Document the date: Write down the date you changed filters 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 your last filter.
  6. Secure the filter: Make sure the new filter fits correctly and close any latches or clips that secure it in the unit.
  7. Turn on your furnace: Once the clean filter is properly secured, you can turn your furnace back on.

Can a Dirty Air Filter Damage My Furnace?

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