What Are the Basics of Furnace Filters?

A furnace filter is there first to protect the equipment and second to clean the air that passes through it. It catches dust, pet hair and other debris before it can coat the blower and the heat exchanger, and it should be checked regularly and changed before it clogs. For a standard 1 inch filter, every one to three months is a common guideline.

What a filter does, and what it does not

Air is pulled from the house through the return ducts, passes through the filter and then goes to the furnace or air handler. The filter traps the larger particles. Its main job is keeping grime off the moving parts and coils. Any air cleaning you get is a bonus, and a standard filter will not catch everything.

That is worth knowing in the Tri-Cities, where fine dust is a fact of summer and wildfire smoke drifts in late in the season. A filter that is clean and correctly fitted helps, but heavy smoke may call for a better grade of filtration, and your system has to be able to handle it.

The main types

• Basic fiberglass filters are thin and inexpensive, and they mostly protect the equipment from large debris.
• Pleated filters have more surface area and catch finer particles, which makes them a common upgrade.
• Washable or electrostatic filters can be cleaned and reused, but they must be fully dry and cleaned on schedule.
• Thick media filters, often 4 or 5 inch, last longer between changes and catch more, and they need a cabinet built for them.

Filters carry a MERV rating that describes how small a particle they capture. Higher is not always better. A very dense filter in a system that was not designed for it restricts airflow, which strains the blower and can cause problems with heating and cooling. Ask a technician which rating suits your equipment before you jump to the highest number.

How often to change it

The one to three month guideline is a starting point. Change filters more often if you have pets, if someone in the house is sensitive to dust, if there has been construction or if a smoky stretch of weather has the system running hard. Thicker media filters may go six months to a year. The simplest habit is to check the filter monthly and hold it up to a light: if you cannot see light through it, change it.

Make sure the filter is the right size and installed with the arrow pointing toward the furnace, in the direction of airflow. Gaps around the edges let dirty air slip past, and a filter installed backward does less.

What to do with the old ones

Most disposable furnace filters are made of mixed materials, and many curbside programs do not accept them. Check with your local waste service. Slip the old filter into a bag as you remove it so the dust stays out of the air.

A note on smoke season and fit

When smoke settles over the Tri-Cities, many people want the best filtration they can get. A better filter can help, but only if your system was built to push air through it. If you cannot tell whether your furnace can handle a denser filter, ask before switching, and do not stack two filters in one slot to get the same result.

Keep a spare filter or two on hand in the right size, and write the size on the edge of the furnace cabinet, or take a photo of the old filter's label. It makes changing on schedule far easier than a last-minute trip to the store.

Air-Tech has been a family-owned business in the Tri-Cities since 2007, and if you are unsure which filter fits your furnace, the team at (509) 392-2021 can help you pick one.