Picking out the right 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 crucial function in keeping its system running safely, efficiently and for a long time.

An overused furnace filter loses its effectiveness, permitting potentially harmful particles to flow through your home. It also limits airflow, which can damage your furnace and shorten its life span.

Making certain 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 delivering healthy indoor air quality for your residence.

The quality of the air your family breathes is important to the heating and cooling pros at Forster Heating. We've long been dedicated to improving indoor air quality in Auburn. 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?

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

Officials suggest checking your furnace filter monthly and replacing it if it’s dirty. You’ll know if your filter needs changing because it will filled with dirt or dust. Those who have dogs and cats will likely have to replace their furnace air filter more often, because a quality air filter will trap pet hair circulating in a home.

Locating Your Furnace's Air Filter

In general, a furnace air filter is normally found in the return air duct or blower compartment before the return air reaches the furnace. This is so air entering the system is filtered before it passes 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, inside the furnace. It's generally housed in a slot, frame or cabinet for easy access and replacement. Always refer to your furnace's owner manual for information about filter location of the furnace in your home.

Is My Furnace Filter Just a Type of Air Filter?

The easy answer is, yes. In HVAC, a furnace filter and an air filter or air conditioner filter are effectively identical. While they might be called different things 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, making certain the air flowing through your home is clean and safe.

What Is the MERV Rating System and What MERV Rating Do I Need?

Once you locate your old furnace filter and figure out when it should be changed, it’s time to pick 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 short for Minimum Efficiency Reporting Values. The MERV rating measures the effectiveness of air filters at trapping airborne particles. The rating scale ranges from 1 to 20, with higher numbers indicating enhanced capabilities to filter tinier particles.

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

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

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 located on the side of the filter frame. The filter should be installed with this arrow pointing in the direction of the furnace or AC, which is the direction of the airflow. If you're doubtful about the airflow direction, remember that air always moves from the return duct and then to the heat or cooling source. Therefore, be sure that the arrow points at the furnace or air conditioner.

Many people struggle with which direction to face their air filter. To help remember, consider snapping a quick photo with your cellular 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 do this is during a routine furnace maintenance visit.

How to Replace Your Furnace Air Filter

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

  1. Turn off your furnace: Be sure to turn off your furnace before starting the process.
  2. Locate the furnace filter: Typically, the filter is found within 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 replacement filter to point in the same direction.
  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 make it easier to keep track of when it's time for the next change.
  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 place.
  7. Turn on your furnace: Once the new filter is safely in place, you can turn your furnace back on.

Will a Dirty Air Filter Damage My Furnace?

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