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

A dirty furnace filter loses its effectiveness, permitting potentially harmful particles to circulate through your home. It also slows airflow, which can damage your furnace and shorten its life span.

Ensuring your furnace uses a clean filter that is appropriate for your needs is not just about keeping your furnace working efficiently. It’s also about delivering healthy indoor air quality for your home.

The quality of the air your family breathes is important to the HVAC pros at H & H Service Company. We've long been dedicated to enhancing indoor air quality in Mechanicsburg. Here, we’ve answered frequent questions about HVAC filters, including that very tricky question of what direction do you point a filter in your furnace or air conditioner?

When Should I Replace My Furnace Air Filter?

Experts stress it's important to replace dirty air filters in a furnace or air conditioner regularly. 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 examining your furnace filter monthly and replacing it if it’s dirty. You’ll know if your filter needs changing because it will be gray or black from dirt or dust. Homeowners who have pets that shed will very likely want to replace their furnace air filter more often, because a good air filter will trap pet hair circulating in a home.

Locating Your Furnace's Air Filter

In general, a furnace air filter is commonly found in the return air duct or blower compartment before the return air reaches the furnace. This is so 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 located on the right, left, bottom or in some cases, within the furnace. It's generally housed in a slot, frame or cabinet for simple access and replacement. Always refer to your furnace's owner manual for important information concerning filter location of the furnace in your home.

Are Air Filters and Furnace Filters the Same Thing?

The easy answer is, yes. In HVAC, a furnace filter and an air filter or air conditioner filter are essentially the same thing. 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 residence.

They each remove 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 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 select a replacement. That means determining 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 molecules. 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 could need a a higher MERV rating.

Which Way to Put 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 unit. Air filters have 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 in the direction of the furnace or air conditioner, which is the direction of the airflow. If you're unsure about the airflow direction, it may be helpful to remember that air always moves from the return duct towards the heat or cooling source. Therefore, make sure the arrow points in the direction of the furnace or AC.

Many people are confused by which direction to point their system's air filter. To help remember, consider snapping a quick photo with your cell 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 perfect time to inquire about this is during a routine furnace maintenance appointment.

Changing Your Furnace's Air Filter

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

  1. Turn off your furnace: Be sure to switch off your furnace before beginning the process.
  2. Find the furnace filter: Typically, the filter is located in 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 clean filter to point in the same direction.
  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 your family keep track of when it's time for you to change it again.
  5. Insert 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 dirty filter you just removed.
  6. Secure the filter: Make sure the new filter fits correctly and close any latches or clips that lock it in the unit.
  7. Turn on your furnace: Once the new filter is safely installed, you can turn your furnace back on.

Can a Dirty Air Filter Damage My Furnace?

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