Air Filters: Your Guide to Choosing and Replacing Them

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

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

Making certain your furnace uses a clean filter that is appropriate for your needs is not merely about keeping your furnace running efficiently. It’s also about delivering good indoor air quality for your home.

The health of your family is important to the HVAC professionals at Schraer Heating & Air Conditioning. We've long been dedicated to bettering indoor air quality in Warrenton. 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 Should I Replace My Furnace Air Filter?

It is 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 inspecting your furnace filter every month and replacing it if it’s dirty. You’ll know if it is dirty because it will filled with dirt or dust. Those who have pets will very likely need to replace their furnace air filter more often, because an effective air filter will trap pet hair circulating in a home.

How to Find the Furnace's Air Filter

In general, a furnace air filter is usually 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 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, within the furnace. It's usually housed within a slot, frame or cabinet for convenient access and replacement. Always refer to your furnace's owner manual for details about filter location of the furnace in your home.

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 people may call them different things based on the current season— summer or winter—they are all filters that clean the air in your residence.

They each eliminate dust, allergens, bacteria and other contaminants from the air that is drawn into the furnace and air conditioning system, making sure the air flowing through your home is clean and safe.

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

Once you track down your old furnace filter and determine when it should be changed, it’s time to select a replacement. That means determining 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 measures the effectiveness of air filters at trapping airborne molecules. The rating scale ranges from 1 to 20, with greater numbers indicating a greater ability to filter smaller particles.

Experts say a filter with a MERV rating between 8 and 13 offers an appropriate balance between having good indoor air quality without overly restricting airflow. However, people with certain health conditions might need to use a filter with a higher MERV rating.

Where to Insert the Air Filter in a Furnace or Air Conditioner

Installing an air filter in a furnace or air conditioner correctly is crucial for the efficient operation of the unit. Air filters have a certain 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 air conditioner, 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 towards the heat or cooling source. Therefore, make certain the arrow points in the direction of the furnace or air conditioner.

Many people struggle with which direction to point their system's air filter. To help remember, consider taking a quick picture 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 be installed. A great time to inquire about this is during a scheduled furnace maintenance appointment.

How to Replace Your Furnace Air Filter

Switching out the filter on your furnace or AC is an easy process. Here is a step-by-step breakdown of how to take out a dirty air filter and exchange it for a new one:

1. Turn off your furnace: Make a point to switch off your furnace before starting the process.

2. Find the furnace filter: Typically, the filter is found within 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 replacement filter to point in the same direction.

3. Slide out the old filter: Be careful not to knock out any dust or debris.

4. Note the date: Write down the date of replacement 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. Slide 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 the dirty filter you just removed.

6. Secure the filter: Make sure the new filter fits securely and close any latches or clips that secure it in the unit.

7. Turn on your furnace: Once the new filter is properly installed, 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 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 operating effectively.