Maintenance & care · August 2026 · HVAC Iowa City
How often to change your furnace filter, really
Ask five companies how often to change a furnace filter and you'll get five confident numbers. The honest answer is that the right interval depends on your house, so the useful advice isn't a number, it's a habit: check it monthly during heating season, and change it when it looks gray and furry instead of white and crisp. For most Iowa City homes that works out to every one to three months, but the check is what keeps you honest.
What moves your interval? Pets shed it shorter. So does remodeling dust, a full house, wood floors that collect and release dust, and cheap thin filters that load up fast. A tight, newer house with no pets can genuinely run longer. The filter itself will tell you, which is why the monthly look beats any calendar rule.
Why it matters more here: runtime. An Iowa City furnace works through a five-month heating season with the windows shut, so whatever the filter catches, it catches at volume, and a clogged filter punishes the system the entire time. Airflow drops, the blower strains, rooms farthest from the furnace go cool first, and in the worst case the furnace overheats and shuts itself down on a safety switch, which reads as a breakdown but started as a two-dollar filter problem. In summer the same clog freezes the AC coil solid.
Finding and reading the filter takes one minute. It lives in a slot where the return duct meets the furnace, or behind a return grille on a wall or ceiling. The size is printed on the cardboard frame. Slide the old one out and hold it up to a light: if you can't see light through it, it's done. Note the arrow on the frame, which points in the direction the air flows, toward the furnace.
Which filter should you buy? A middle-of-the-road pleated filter suits most systems. The thin see-through ones barely filter, and the densest allergy filters can actually choke airflow on some blowers. If anyone in the house has allergies or you're not sure what your system can handle, ask us during a tune-up and we'll match the filter to the blower, not to the marketing.
That's the whole guide: look monthly, change when gray, buy sensible pleated, mind the arrow. It's the cheapest maintenance in this trade, and in a heating season like ours it quietly outperforms gadgets ten times its price. And if a filter change doesn't fix a comfort problem, that's when it's worth a call.