Guide to Air Filters: How to Choose and When to Replace It

Selecting 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 role in keeping its system working safely, efficiently and for a long time.

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

Making sure your furnace uses a clean filter that is suitable for your needs is not merely about keeping your furnace operating efficiently. It’s also about creating healthy indoor air quality for your residence.

The quality of the air your family breathes is important to the HVAC pros at Three Rivers Heating and Cooling. We’ve long focused on enhancing indoor air quality in Portland. 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?

When to Replace the Air Filter in Your Furnace

Experts stress it’s important 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 effort to pull air through the plugged-up filter.

Officials recommend examining 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 filled with dirt or dust. People who have pets that shed will likely want to replace their furnace air filter more often, because an effective 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 goes back into the furnace. This ensures air entering 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, inside the furnace. It’s typically housed inside of a slot, frame or cabinet for convenient access and replacement. Always refer to your furnace’s owner manual for facts concerning filter location of your particular brand and model of furnace.

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 conditioning filter are basically the same. 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 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 distributed throughout your home is clean and safe.

What Are MERV Ratings and What MERV Rating Do I Need?

Once you locate your old furnace filter and figure out when it should be substituted for a clean one, it’s time to pick a replacement. That means deciding on the level of filtration that you need. One approach to this is by choosing an appropriate MERV rating for your needs.

MERV stands for Minimum Efficiency Reporting Values. The MERV rating calculates 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 small particles.

Experts say a filter with a MERV rating between 8 and 13 offers an ideal balance between having good indoor air quality without unnecessarily restricting airflow. However, people with some health conditions might need to purchase a filters with a higher MERV rating.

Which Way to Put the Air Filter in a Furnace or Air Conditioning System

Putting an air filter in a furnace or air conditioner correctly is important for the efficient operation of the unit. Air filters are designed to be installed in a specific 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 at the furnace or AC, 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 and then to the heat or cooling source. Therefore, make sure the arrow points toward the furnace or air conditioning unit.

Many people have difficulty remembering which direction to face their system’s air filter. To help remember, consider taking a picture 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 be installed. A great time to inquire about this is during a scheduled furnace maintenance appointment.

How to Change a Furnace Air Filter

Changing the filter on your furnace or AC is a simple 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 sure to shut 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 clean filter to point in the same direction.
3. Take out the old filter: Be mindful not to knock out any dust or debris.
4. Record 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 the next change.
5. Insert 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 securely and close any latches or clips that hold it in the unit.
7. Turn on your furnace: Once the new filter is completely installed, you can turn your furnace back on.

Will a Dirty Air Filter Damage My Furnace?

The shortest answer is, yes, a dirty air filter can cause a furnace to stop working or shorten its lifespan. Changing your furnace or air conditioning filter is one of the easiest things you can do to keep your system running effectively.