The recommended change frequency for Nordic Pure filters depends on the specific model's MERV rating: MERV 8-10 – Replace every 3-6 months, MERV 11-13 – Replace every 6-9 months, MERV 14-16 – Replace every 9-12 months. Check your Nordic Pure filter each month as well. If it appears very dirty or clogged, change sooner than the recommended interval. Replacing promptly preserves HVAC system air flow.