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Filter Replacement Schedule
Quick answer: Enter your filter depth, number of pets, whether there is smoking, renovation or heavy dust, and whether the system runs heavily. The tool starts from a typical interval — three months for 1-inch, nine for 4-inch — and shortens it for each factor. It returns a suggested interval and a check-by date. Inspect monthly regardless.
The rule set
Starting points: 1-inch 3 months, 2-inch 4, 4-inch 9, 5-inch 10. Each pet subtracts half a month (up to three pets); smoking, renovation or heavy dust subtracts one month; heavy runtime, such as a heat pump or continuous fan, subtracts half a month. Floors are 1 month for thin filters and 3 for deep media. These are common guideline patterns, not maker specifications.
Worked example
A 1-inch filter with two dogs and heavy runtime: 3 − 1 − 0.5 = 1.5 months. A 4-inch filter in the same home: 9 − 1 − 0.5 = 7.5 months.
Illustrative note (2026-10-29): Example inputs were set on 2026-10-29 for illustration.
Limits
Replace sooner if the upstream face is evenly grey, the filter bows or airflow drops. Follow your filter and equipment makers' guidance.