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Merv 11 should be plenty for most all allergens (typically jsut dust, pollen and mold spores). Keep in mind, the primary function of a filter to to keep dust from accumulating over hte fins on the indoor coil and heat exchanger and and to prevent recirculating airborn dust as much as reasonably possible. With this in mind, it's mot a dust collector and won't more nearly enough air to act as a primary filtration system. For example, the airflow and air exchange rate at a hospital or pharmaceutical manufacturing facility can be 10 air changes per hour or more. A properly sized residential system running on low continuous fan will probaly be around 2-3 ACH.
The best weapon against dust in a home is a good quality vacuum cleaner with a HEPA filter used at minimum once a week, more often if needed. More often with higher occupancy or if you have carpet. Don't forget, the majority of dust is mainly lint, dead skin cells, hair and fine soil/dirt from outdoors.
Some standard 20x25x5" media filter like a Trion Air Bear have a MERV 13 Option. I typically use that in my home. I have 2 systems that are 2 tons each so that filter can last nearly a year in my set-up. They are very inexpensive filter housings and filter are pretty rasonably prices and most supply houses stock a generic version locally. They also have a pretty slick right angle verson too for retrofit installations where you have limited width bewteen the return and the furnace.
Originally Posted by wahoo67
