How Do Furnace Filter Sizes Work

Posted by Service Champions

Air Conditioning Blog

Furnace Filter Sizes

What are furnace filter sizes? Do furnace filter sizes affect indoor air quality? Or home comfort? What furnace filter sizes have to do with energy efficiency and HVAC spending costs?

With all the numbers and metrics printed on the box of furnace air filters, it is easy to grow overwhelmed.

Furnace filter sizes are different from other measurements. As long as homeowners know how to read them and where to find them, they should have little trouble replacing furnace filters at home.

Homeowners should always know their furnace filter sizes in order to:

Purchase new furnace filters
Successfully replace old furnace filters
Maintain healthy indoor air
Protect their furnace and air conditioner
Prevent HVAC repairs and damages

Using the wrong furnace filter sizes causes all sorts of issues. Homeowners should always use the correct furnace filter sizes in order to protect their home comfort, indoor air quality and lower HVAC costs.

How To Read Furnace Filter Sizes

What measurements go into furnace filter sizes? There are three different calculations included in furnace filter sizes.

Length
Width
Depth

Almost always, furnace filter sizes are printed on the side of the filter. They are read as Length x Width x Depth.

When inspecting furnace filters, homeowners may find two different sets of sizes. First, there is the nominal size expressed in whole numbers. Then, there is the actual size, which typically runs half an inch shorter than the nominal size.

For example, the nominal size of one of the most popular furnace filter sizes is 20 x 25 x 1 inches. The actual furnace filter size measures to 19.5 x 24.25 x 0.75 inches.

Nominal sizes are used to simplify furnace filter sizes. Rest assured, most furnace filters have both sizes printed on the sides.

Finding the Right Furnace Filter Sizes for Your Furnace

The simplest way to find furnace filter sizes is to remove the existing furnace filter and check the label. If the old furnace filter has already been discarded, consult the furnace user manual for this information. If you no longer have the user manual, check with the furnace manufacturer. Lastly, you talk your HVAC specialist.

The furnace you have determines the furnace filter sizes used. However, homeowners usually can choose from different brands of furnace filter sizes.

Popular Brands for Similar Furnace Filter Sizes

Aprilaire
Carrier – Bryant
Honeywell
Lennox
Toptech
Totaline
Trion Air Bear
Skuttle

Furnace Filter Sizes for Indoor Air Quality

The depth or thickness of furnace filter sizes determines what it can do for indoor air quality. The thickness of furnace filter sizes ranges from one inch to five inches.

Furnace filter sizes with a thickness or depth of one inch typically need to be changed more frequently. The thicker the furnace filter, the less it needs be replaced. Why?

Furnace filters with greater thickness or depth have more layers and more surface area. These additional layers act as extra nets to capture airborne particles that may have gotten through the first layer. As a result, these furnace filter sizes last longer and capture more. While these do cost more, they also deliver more benefits.

When homeowners opt for furnace filter sizes with a greater depth, they choose a furnace filter that:

Holds more particles
Doesn’t restrict airflow
Lasts longer

The thicker the furnace filter, the longer homeowners can go without replacing it. Typically, furnace filter sizes with a thickness or depth up to one inch need to be replaced once every one to three months. In contrast, furnace filter sizes with a thickness of four inches last up to one full year.

Generally, the furnace determines the furnace filter sizes. However, homeowners who want to upgrade their air filters to a greater depth just need to do a little more work to make it possible.

Which homeowners benefit from thicker furnace filter sizes? Homeowners who want:

Better energy efficiency
Improved indoor air quality
Less air filter maintenance time
A stronger central air system

If your current furnace only allows for furnace filter sizes with a depth of one inch, HVAC contractors can modify the furnace to accommodate larger sizes. This does take work and time. However, homeowners get to use better furnace filter sizes that do more for home comfort. They also worry less about their furnaces.

Making these technical adjustments means that the furnace can hold larger and stronger furnace filter sizes for better indoor air quality and energy efficiency.

Homeowners also do need to keep in mind that other factors determine just how frequently air filters need replacement.

What else determines the frequency of air filter changes?

Home construction and insulation
Indoor air pollutants
Number of people or animals in the home
Ventilation
Condition of the furnace and air conditioner
Lifestyle goals and needs

Homeowners having trouble collecting this information should work with their HVAC experts. Heating and air conditioning technicians can accurately assess the home, indoor air quality and lifestyle goals for the perfect furnace filter sizes.

Furnace Filter Sizes and MERV Ratings

Furnace filter sizes in an L x W x D format should not be confused with MERV ratings.

MERV stands for minimum efficiency rating value. It refers to the pore size of the air filter material. A higher MERV rating means that the pore is smaller, catching more particles.

No matter the furnace filter sizes, there also come MERV ratings or numbers.

Furnace filter sizes with a MERV rating between 1 and 4 capture airborne particles like:

Pollen
Dust and dust mites
Sanding and spray paint dusts
Fibers from textiles and carpets

Furnace filter sizes with a MERV rating between 5 and 8 also capture airborne particles like:

Microbiological growth
Hair sprays and cleaning sprays
VOCs
Cement and pudding mixes

Furnace filter sizes with a MERV rating between 9 and 12 also capture airborne particles like:

Auto emissions and fumes
Dust from lead, flour and humidifier
Legionella

While a higher MERV rating seems like the better option, they do cost more and use more energy. Homeowners with homes that do not need higher MERV-rated furnace filter sizes should opt for a more appropriate size in order to cut down on unnecessary costs and energy spending.

Furnace Filter Sizes for Energy Efficiency and Cost Savings

Furnace filter sizes are important in maintaining energy efficiency. Using the wrong furnace filter sizes causes all sorts of issues that cost homeowners time and money.

Furnace filters must fit just right inside the furnace with no gaps or spaces. If there are gaps, there is too much room for error.

Using the wrong furnace filter sizes results in:

Dirty indoor air
Stubborn and damaging buildup
High energy spending
Irregular heating and air conditioning
Expensive repairs
Permanent damages

What can homeowners do to prevent these issues? Use the correct furnace filter sizes and replace as needed. Fortunately, air filters are relatively affordable and deliver benefits that outweigh the initial costs. Simply using a clean air filter cuts down on HVAC energy spending by 15 percent.

For homeowners who want to save on costs, air filter care habits also matter.

As a rule of thumb, homeowners should always:

Wipe down vents and registers
Keep the home clean
Ventilate the home
Replace the air filter as needed
Schedule HVAC maintenance twice a year

Homeowners new to furnace filter care may be put off by the cost of buying new furnace filters. However, using an old or dirty air filter causes more harm than the small savings are worth. Using old air filter racks up enormous utility bills, expensive damages and repairs and terrible home comfort.

By utilizing these simple habits for air filter care, homeowners cut down on technical troubles and wasteful energy spending. As a result, they enjoy clean indoor air, a healthy central air system and reliable heating and air conditioning.

Check Furnace Filter Sizes with Service Champions HVAC Experts

Service Champions Heating & Air Conditioning is the Diamond Certified HVAC provider for Orange and Los Angeles Counties. We lead in heating and air conditioning repairs, installations, maintenance and advanced air care solutions. The homeowners of California trust us in their homes.

Our experts promise your total satisfaction. From start to finish, we always deliver exceptional customer care with our superior technical service to give you the best.

To meet with Service Champions for help on furnace filter sizes, complete the form below. You can also speak to our call center representatives for more information.