Choosing the proper 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 vital role in keeping its system working 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.

Making sure your furnace uses a clean filter that is suitable for your needs is not only about keeping your furnace running efficiently. It’s also about providing healthy indoor air quality for your household.

The health of your family is important to the heating specialists at Air Current AC & Heat. We've long worked with an eye on improving indoor air quality in Houston. Here, we’ve answered common questions about HVAC filters, including that especially 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 vital to replace dirty air filters in a furnace or air conditioner periodically. Dirt-clogged filters cause the system to worker harder than it should because it takes more energy to pull air through the plugged-up filter.

Officials suggest checking your furnace filter monthly 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 dogs and cats will very likely want 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 found in the return air duct or blower compartment before the return air gets to the furnace. This makes sure air entering the system is filtered before it moves 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, on the inside of the furnace. It's typically housed within a slot, frame or cabinet for simple access and replacement. Always refer to your furnace's owner manual for facts concerning filter location of your furnace.

Is My Furnace Filter Just a Type of Air Filter?

The simple answer is, yes. In HVAC, a furnace filter and an air filter or AC filter are basically the same. While they might be called different things based on the current season— summer or winter—they are all filters that clean the air in your HVAC system.

They each eliminate dust, allergens, bacteria and other particulates from the air that is drawn into the furnace and air conditioning system, ensuring the air circulating throughout your home is clean and safe.

What Is a MERV Rating and What MERV Rating Should I Have?

Once you locate your old furnace filter and determine when it should be substituted for a clean one, it’s time to choose a replacement. That means picking the level of filtration that you need. One way to do that is by choosing 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 an ideal balance between having healthy indoor air quality without needlessly restricting airflow. However, people with specific health conditions may need to use a filter with 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 have a specific direction, indicated by an arrow written on the side of the filter frame. The filter should be installed with this arrow pointing at 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 towards the heat or cooling source. Therefore, be sure that the arrow points in the direction of the furnace or air conditioning unit.

Many people have difficulty remembering which direction to point an 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 go. A great time to ask about this is during a scheduled furnace maintenance appointment.

How to Replace Your 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 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 positioned in 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 clean filter to point in the same direction.
  3. Slide out the old filter: Be mindful not to knock out any dust or dirt.
  4. Document the date: Write down the date you replaced the filter on the new filter's frame. This will help your family keep track of when it's time for the next change.
  5. Insert 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 your last filter.
  6. Secure the filter: Make sure the new filter fits securely and close any latches or clips that secure it in the compartment.
  7. Turn on your furnace: Once the clean filter is properly secured, you can turn your furnace back on.

Will a Dirty Air Filter Damage My Furnace?

The simple answer is, yes, a dirty air filter can cause a furnace to cease working or decrease its lifespan. Changing your furnace or air conditioning filter is one of the best things you can do to keep your system running correctly.