One of the prerequisites for efficient furnace heating in homes is a properly sized air filter.
You’d be surprised by how many sizes there are.
If you’re unsure which size air filter to buy for efficient heating and keeping your energy bills minimal, this guide is for you.
We have mapped out the best way to determine your furnace’s air filter size.
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The Best Way to Determine Furnace Air Filter Size — Measuring the Compartment
There are several ways to figure out what size air filter you need, but for most of them, you need an existing air filter.
If you don’t have an old air filter in the furnace’s compartment, that rules out reading the printed dimensions or measuring the air filter.
This leaves us with measuring the compartment itself. The only things you need are a measuring tape and a flashlight.
Here’s how to measure the slot. Check out the compartment where the air filter is supposed to go.
You should be able to see a filter track of about 1″. This is where the filter fits into. Measure the compartment’s length, width, and depth.
The size dimensions would look something like 13x18x1, 17x21x1, 8x8x1, etc.
Visit this link to see all options for air filter sizes.
Once you get the exact figures, you can buy an air filter that snugly fits the compartment.
Remember that the dimensions you’d see online would be nominal sizes, not actual ones.
So choose the rounded size while buying air filters online.
We’ll talk about the actual and nominal size air filters later.
If you’re still confused about the right air filter for your furnace, you can speak to the manufacturer directly.
If not, you can consult an air filter expert.
Other Ways of Determining Furnace Air Filter Size
If you have an old air filter, things are much easier for you.
If you’re lucky, the nominal filter size is printed on the frame of the old air filter.
Simply punch in the size on Google and check out if any nearby vendors have filters in the size you need — which most of them would.
If the air filter dimensions are not on the frame, or if they have faded and become illegible, then you have to measure the old air filter.
Use a measuring tape, and jot down the air filter’s length, width, and depth.
Once you know its size, you can order filters and stock up for the next several months.
Remember that size is not the only factor that decides the best air filter for your furnace.
You must also consider the filter’s MERV rating and your furnace’s handling capacity.
MERV is the metric used to measure the efficiency of the air filter.
The higher the rating value, the better the air filter’s efficiency and the more your furnace’s handling capacity needs to be.
If the furnace and MERV rating is incompatible, it will face issues, which could increase your energy bills.
Speak to a professional if you’re unsure what MERV rating is right for your furnace.
They can take a look at your furnace and tell you the right size and MERV rating air filter for it.
Nominal Size vs Actual Size
One thing you need to be mindful of while buying an air filter is the difference between the nominal size and the actual size.
As the name suggests, the filter’s actual size is its exact measurements.
They are accurate down to one-eighth of one inch.
The nominal size is the measurements printed on the air filter by the manufacturer.
These figures are rounded up to the closest whole inch.
If the actual size of an air filter is 13¾” x 13¾” x ¾, the dimensions you’d see printed on the air filter are 14″x14″x1″, which would be its nominal size.
If you’ve measured the air filter compartment of the furnace, look for air filter sizes closest to the figure you have measured.
While buying online, all the sizes you see are nominal.
Keep that in mind while shopping.
If you’re not sure how to go on about buying the right size air filter or still have questions about it, speak to a professional.
They can help you navigate different air filter sizes. This is the Best Way to Determine the Best Air Filter Size for Your Furnace.
