Filterbuy 17x26x4 Air Filter MERV 13 Optimal Defense (2-Pack), Pleated HVAC AC Furnace Air Filters Replacement for Lennox x6664 (Actual Size: 16.56 x 25.94 x 4.13 Inches) - Amazon.com
16 x 25 x 5 Air Filters at Lowes.com
MERV: 11 Air Filters at Lowes.com
Lennox X6670 MERV 11 Box Replacement Filter also for Honeywell, 16" H x 25" L x 5" W - Humidifier Replacement Filters - Amazon.com