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How to Find the Right HVAC Filter Size

How to Find the Right HVAC Filter Size

Replacing your HVAC filter is an important part of HVAC maintenance and keeps your system running safely and efficiently. Of course, it’s much easier to change your filter when you know what size and type you need.

Shopping can be overwhelming, but you never want to guess at the right size for your filter. With just a little know-how, you can get the right HVAC filter size without a lot of stress or hassle. You can also change it yourself, but if you prefer, you can bring in a pro to do it for you.

Why Does the HVAC Filter Size Matter?

If your air filter is too big, you simply can’t cut it to fit into your HVAC system. That only allows contaminants and air to escape, defeating the purpose of having a filter in the first place and wasting energy.

Image: air filter cat meme. If this cat reminds you of your filter, you should probably change it!
Conversely, an air filter that’s too small will create air gaps and allow particles to come in, impacting your air quality and energy efficiency. Neither option is good for your home or your health, so you have to get an air filter that fits properly.

Look at Your Existing Air Filter

The quickest and easiest way to determine the size for your new HVAC filter is by checking the old filter. Most air filters have a size printed on the side of the frame, with the length, width, and depth measured in inches.

For example, your air filter may read “16x20x1,” meaning that it is 16 inches in length, 25 inches in width, and one inch in depth. Once you know this size, you can purchase a new filter with the same dimensions. Remember, the filter has to be the right size to avoid issues with your air quality or energy usage.

Measure It Yourself

If your current air filter doesn’t have measurements printed, you can measure it yourself easily. All you need is a measuring tape to determine the length, width, and depth of your air filter.

Keep in mind that air filter dimensions listed are typically slightly larger than the size of the air filter itself. For example, if your air filter measures at 16 inches, 20 inches, and one inch, the actual measurements may only be 15.75 inches, 19.75 inches, and .75 inches, but the new air filter will fit if it’s listed as 16x20x1. Round up to the nearest inch, if necessary.

Measure Air Register or Air Filter Slot

If the previous methods aren’t possible, such as with a missing air filter, you can measure the slot that the air filter goes into. This will help you determine what size air filter is appropriate.

Image: an air filter sticking out of its slot on the side of a furnace. If your air filter doesn't have the size printed on it, you can measure the slot to determine the HVAC filter size.
In this case, the air filter slot is the actual air filter size, so the slot may measure slightly smaller than the size of the air filter that you need to purchase. Similarly, you can round up to ensure you’re getting the right size.

Where Is the Air Filter Located?

Air filters are typically located in the return air intake on the furnace. Look for the area where the return duct comes into your furnace, and you should see a plate that covers the air filter slot.

Image: an HVAC tech inserting a clean filter into a furnace.
Some HVAC systems don’t have air filters in the air handling unit. In this case, the air filter will probably be located near the return vent inside your home. If so, changing the filter is a quick and simple process. You just have to be able to reach the vent to change the filter safely.

Know Your Air Filter’s MERV Rating

Aside from size, you’ll also need to determine the MERV rating for your air filter before replacing it. This is a measurement of how effective the air filter is at removing particles from the air. The higher the MERV rating, the more effective the filter will be at removing small particles from the air.

So, a higher MERV rating is better, right? Not necessarily. If you have a high MERV rating on your filter, the filter will be thicker. This means your HVAC system will have to work harder to circulate the air through your home, using more energy and increasing your utility bills.

Ideally, homes should have a MERV rating of 5 to 8. This range provides good filtration and will remove pollen, dust mites, and mold spores. Your system will also run efficiently, as long as you’re diligent about replacing the filters as needed.

That said, if you have allergies, asthma, or respiratory conditions, then a filter in the range of 10 to 12 may be the better choice. These ratings ensure the filter can trap allergen particles as small as one micron, which encompasses mold spores, pollen, and automotive exhaust.

Do you need to change your air filter or other HVAC repairs or replacements? Contact Adeedo to schedule your appointment!

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