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

8/16/2023

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Selecting 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 critical function in keeping its system operating safely, efficiently and for a long time.

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

Ensuring your furnace uses a clean filter that is appropriate for your needs is not just about keeping your furnace running efficiently. It’s also about creating good indoor air quality for your household.

The health of your family is important to the heating specialists at AC Sales. We've long been dedicated to improving indoor air quality in Lafayette. Here, we’ve answered frequent 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 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 more energy to move air through the plugged-up filter.

Officials recommend checking your furnace filter every 30 days and replacing it if it’s dirty. You’ll know if it is dirty because it will be gray or black from dirt or dust. Those who have pets that shed will very likely need 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 installed in the return air duct or blower compartment before the return air gets to the furnace. This is so air flowing into the system is filtered before it passes through the furnace components and is heated.

Depending on the type of furnace, the filter may be positioned 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 information regarding filter location of the furnace in your home.

Is a Furnace Filter the Same as an Air Filter?

The straightforward answer is, yes. In HVAC, a furnace filter and an air filter or air conditioning 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 home.

They each eliminate dust, allergens, bacteria and other airborne debris 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 Are MERV Ratings and What MERV Rating Should I Have?

Once you track down your old furnace filter and determine when it should be substituted for a clean one, it’s time to select a replacement. That means deciding on the level of filtration that you need. One method to do this is by choosing an appropriate MERV rating for your needs.

MERV is an abbreviation 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 greater 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 adequate indoor air quality without overly restricting airflow. However, people with some health conditions may need to use a filter with 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 the proper way is crucial for the efficient operation of the heating or cooling system. Air filters have a certain 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 in the direction of the furnace or air conditioner, 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 certain the arrow points at the furnace or air conditioner.

Many people have difficulty remembering which direction to install their system's 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 perfect time to ask about this is during a routine furnace maintenance call.

How to Replace Your Furnace Air Filter

Replacing the filter on your furnace or air conditioning system is a simple process. Here is a step-by-step list 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 starting the process.
2. Locate the furnace filter: Typically, the filter is found within the furnace or in the air return vent. Take 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. Remove the old filter: Be diligent not to knock out any dust or debris.
4. Record 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 the next change.
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 the dirty filter you just removed.
6. Secure the filter: Make sure the new filter fits correctly and close any latches or clips that lock it in the compartment.
7. Turn on your furnace: Once the clean filter is completely secured, you can turn your furnace back on.

Can a Dirty Air Filter Damage My Furnace?

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

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