Most homes should change furnace filters about every 1–3 months, but the exact timing depends on filter type and how heavily the system is used.
General timing
For standard 1-inch disposable filters, a common guideline is to replace them every 30–90 days. Many experts recommend checking the filter monthly and changing it as soon as it looks dirty, especially in peak heating or cooling seasons.
Filter thickness and rating
Thicker or higher-end filters usually last longer than thin, basic ones. As a rough guide, 1–2 inch filters are often changed every 1–3 months, 3–4 inch filters every 6–9 months, and 5–6 inch filters every 9–12 months, assuming normal conditions.
Home and lifestyle factors
You may need to change filters more often if you run the furnace or AC a lot, have pets, or have allergy or asthma sufferers in the home. In those cases, many pros suggest checking monthly and changing every 30–60 days during heavy use.
Why changing matters
A clogged filter restricts airflow, which can reduce comfort, increase energy bills, and strain or even damage the furnace over time. Regular changes also help keep dust and other particles from recirculating, improving indoor air quality.
Simple rule of thumb
Check the filter once a month and replace it whenever it looks gray or visibly dirty, or if you can’t remember the last time it was changed. When in doubt, changing a bit early is safer for both your system and your air quality.
