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 vital function in keeping its system running safely, efficiently and for a long time.

A clogged furnace filter loses its effectiveness, enabling potentially harmful particles to flow through your home. It also restricts airflow, which can damage your furnace and shorten its life span.

Ensuring your furnace uses a clean filter that is ideal for your needs is not merely about keeping your furnace running 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 pros at Lanz Furnace and Fireplace. We've long focused on enhancing indoor air quality in Monroe. Here, we’ve answered common questions about HVAC filters, including that particularly 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's critical 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 pull air through the plugged-up filter.

Officials recommend examining your furnace filter every month and replacing it if it’s dirty. You’ll know if your filter needs changing because it will filled with dirt or dust. People who have dogs and cats will probably want to replace their furnace air filter more often, because a good 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 found in the return air duct or blower compartment before the return air goes back into 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 brand, the filter may be found on the right, left, bottom or in some cases, within 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 facts about filter location of your particular brand and model of furnace.

Is a Furnace Filter the Same as an Air Filter?

The easy answer is, yes. In HVAC, a furnace filter and an air filter or air conditioning filter are effectively the same. While they might be called different things 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, ensuring the air distributed throughout your home is clean and safe.

What Is a MERV Rating and What MERV Rating Do I Need?

Once you find your old furnace filter and figure out when it should be changed, it’s time to select 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 stands 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 smaller particles.

Experts say a filter with a MERV rating between 8 and 13 offers an ideal balance between having healthy indoor air quality without overly restricting airflow. However, people with specific health conditions might need a a higher MERV rating.

Which Way to Put the Air Filter in a Furnace or Air Conditioner

Installing an air filter in a furnace or air conditioner the proper way is important for the efficient operation of the heating or cooling system. Air filters are designed to be installed in a particular direction, indicated by an arrow written on the side of the filter frame. The filter should be placed in the unit with this arrow pointing toward the furnace or AC, which is the direction of the airflow. If you're doubtful about the airflow direction, it may be helpful to remember that air always moves from the return duct and then to the heat or cooling source. Therefore, make sure the arrow points toward the furnace or air conditioner.

Many people have difficulty remembering which direction to point their air filter. To help remember, consider snapping a quick photo with your mobile phone after the filter has been accurately 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 routine furnace maintenance call.

How to Change a Furnace Air Filter

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

  1. 1. Turn off your furnace: Make a point to shut off your furnace before beginning the process.
  2. Find the furnace filter: Typically, the filter is positioned 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 the same way.
  3. Take out the old filter: Be mindful not to knock out any dust or particles.
  4. Record the date: Write down the date you changed filters on the new filter's frame. This will make it easier to keep track of when it's time for you to change it again.
  5. Put 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 correctly and close any latches or clips that secure it in the compartment.
  7. Turn on your furnace: Once the clean filter is safely in place, you can turn your furnace back on.

Will a Dirty Air Filter Cause a Furnace Not to Work?

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