Why your filter matters more than you think

If we could pick one homeowner habit that prevents the most service calls, it would be "change the filter on schedule." That's it. That's the post.

OK, a little more.

What the filter actually protects

The filter isn't really there for your lungs (though clean filters do help). Its main job is to protect the indoor coil and the blower motor from a coating of dust that, over a year or two, becomes a felted insulating layer that reduces airflow and heat transfer. A coil that can't transfer heat efficiently has to run longer, which means higher bills, more wear, and eventually a frozen coil in summer or a tripped high-limit in winter.

How often to change it

• 1-inch fiberglass or pleated filters: every 30–60 days during heavy use, every 90 days in mild weather. Faster if you have pets or someone with allergies.
• 4-inch (5-inch) media filters in a dedicated cabinet: every 6–12 months. Mark the install date on the cardboard frame with a Sharpie.
• Washable electrostatic filters: rinse monthly during heavy use. Let dry fully before reinstalling.

What MERV rating to buy

Higher MERV = finer filtration but more airflow restriction. A residential system designed for a basic 1-inch filter cannot handle a high-MERV "hospital grade" filter — you'll choke airflow and cause exactly the problems the filter was supposed to prevent.

• MERV 8: the standard. Good general filtration, low airflow penalty. Fine for most homes.
• MERV 11: a step up for households with pets or mild allergies. Most modern systems handle it without complaint.
• MERV 13: only if your system was sized for it (4-inch cabinet, properly designed return). Don't drop one of these into a 1-inch slot.

The bigger picture

If you can't remember the last time you changed it, it's time. If you don't know what size it is, write it on the side of the cabinet so you don't have to measure again next time. And if you'd rather not deal with it at all, our maintenance plan covers two visits a year and we bring the filters with us.