HOMEOWNER GUIDE · FURNACE FILTERS

Furnace Filters: How to Choose and Change One

A clean, correctly installed filter helps your heating and cooling system move air as designed. Here are a few simple things to check before you replace yours.

By Wilcox Heating and Cooling · Randolph, Wisconsin

Start with the filter your system calls for

Check the size printed on the filter you are removing. If it is missing or hard to read, look in the equipment manual or on the filter rack for the required size. A filter that is too small can leave gaps; one that does not fit can be difficult to install correctly. Don’t force it into the slot.

Point the arrow toward the furnace

Most disposable filters have an arrow on the frame showing airflow direction. Install the filter so the arrow points toward the furnace or air handler’s blower. If the arrow is hard to see, take a photo of the old filter before removing it and follow the equipment or filter instructions.

Check it monthly

Check your filter about once a month, especially during periods when the system runs often. Dust, pets, home conditions, and the filter itself can all affect how quickly it loads up. Follow the replacement interval on the filter and the instructions for your equipment; replace it sooner if it is visibly dirty or airflow seems restricted. The U.S. Department of Energy advises checking filters monthly and replacing them at least every three months.

Choose a compatible filter

Use the filter type and rating recommended for your system. A higher number on the package is not automatically the right choice for every furnace. If you want to change filter type or rating, check your equipment documentation or ask an HVAC professional to confirm it is suitable.

When to ask for help

If you can’t find the filter slot, the filter will not fit, or you are unsure which replacement your system needs, stop before forcing anything. A technician can help locate the filter and confirm the correct size and type.