20x21_1/2x1 Exact MERV 12 Plus Carbon AC Furnace Filters 6 Pack spl_hf Use High Altitude model at

Use High Altitude model at 4500 ft elevation or above

Plant Growth Promoting Substrate (trace minerals for flower development

and landscape plants

and high output in any growing environment

You will need either a pump or a valve

20x21_1/2x1 Exact MERV 12 Plus Carbon AC Furnace Filters 6 Pack spl_hf Use High Altitude model atNordic Pure Custom MERV 12 Plus Carbon air filters are made based on the actual measurements so be sure to measure your current filter to get the EXACT dimensions before ordering. As with all Nordic Pure filters, the effective life of your filter depends on the environment in which you live. We recommend changing 1 and 2 filters every 30 90 days. Our 4, 5 and 6 inch thick filters could last up to 6 months. EXACT MEASUREMENT: Furnace and air condition