Guides

Plain-language explainers on sizing, fitment and replacement. Model-specific numbers live on the model pages; these guides cover the rules that apply across all of them.

Guide7 min What Size Air Filter Do I Need? The size is almost always printed on the filter already in your system. Here is where to look, how to measure when the print has worn off, and the rounding rule that trips most people up. Updated July 2026Read Guide8 min How Often Should You Change an Air Filter? The 90-day rule is a ceiling, not a schedule. Depth, run hours and what is in your air all move the number — and a five-second light test beats every estimate in this guide. Updated July 2026Read