How to Find a Furnace Filter Size

Keep the air coming out of your vents free of dust and dirt. Change your furnace filter regularly.

Regularly replacing your furnace filter will not only improve the operation and extend the life of your furnace, but it can also improve your health and the air quality in your home by keeping dust, dirt and other particulates out of the air you breathe. In most furnaces, replacing the air filter is simply a matter of sliding the old one out and sliding the new one in. The hardest part is figuring out what size filter fits your furnace.

Things You'll Need

• Measuring tape
• Pen
• Paper

Instructions

Filter

1. Open the furnace cover and locate the filter. In most furnaces, the filter is located in the blower compartment, which is on the bottom half of the furnace. The filter is also usually in a vertical slot, but can also be in a horizontal slot.
   If it turns out the filter slot is empty, proceed to Section 3.

2. Slide the filter out of the slot.

3. Look on the filter for markings that indicate the size in inches. In most cases, the filter measurements can be found on one of the thin edges or sides of the filter frame, but sometimes they will be printed on the the surface of the frame next to the filter fabric.

4. Write down the measurements to take to the store with you. If you do not find a filter the exact size of your measurements, visit the U.S. Home Filter link in the Resources section and look at the filter sizes chart to find the closest standard size filter that is just smaller than your measurements.

5. If you cannot locate the measurements on the filter, proceed to Section 2.

Measure Filter

1. Use the measuring tape and measure the width of the filter in inches. Write down the measurement.

2. Measure the length of the filter and also write this measurement down.

3. Measure the thickness of the filter, and mark down the measurement.

4. Take the measurements to the store with you to purchase a new filter. You may want to compare your measurements to the standard filter size chart at the U.S. Home Filters link in the Resources section. Choose the standard size filter that is closest to, but smaller than, your measurements.

Measure Filter Slot

1. Measure the width of the filter slot and write it down.

2. Measure the length of the filter slot and also write it down.

3. Measure the thickness of the filter slot and mark it down.

4. Use these measurements to select a filter, choosing the standard size filter that is nearest to the measurements you took, but only slightly smaller so that it will slide in and out of the slot. You may also want to visit the U.S. Home Filter link in the Resources section and look at the filter sizes chart to find the standard size filter that corresponds to your measurements.

Tips & Warnings

• Once you've found the standard size filter you need, save time by calling around to stores in your area to see if they have the size you need in stock. Some stores only stock certain size furnace filters and may not carry the size you need.

• If you need to buy a furnace filter in a size that is different from your measurements, buy one that is slightly smaller. A larger filter may not fit into your furnace.

Resources

• U.S. Home Filter---Filter Size Chart