Air De-Stratification with Air Filtering

Most buildings suffer from air stratification, in which air near the ceiling and upper floors is warmer than air near the floor and lower floors. This can be mitigated by constantly running the furnace/air conditioning fan.

For new construction and for motivated remodels, provide a product that contains one (maybe two fans inline depending on length of duct), ductwork, two endcaps, filter and UV. During construction, run a duct from the ceiling to the floor (or upper level to lower level). The fan would run constantly to slowly pull air "down", filter the air, and clean air with UV. The fan + filter enclosure + UV with a couple end-caps to expose in drywall could be sold as a kit. The ductwork and additional filters could be bought at a hardware store. A subscription package of montly filter change and yearly UV light change could be sold.

Less air stratification creates a more uniform atmosphere with may result in less furnace/AC cycling which will save money. The additional air filtering and UV germ killing will create a healthier breathing environment.

The ductwork should be narrow enough to pass in drywall cavity or plumbing run, and the main unit should be accessible for homeowner filter maintenance.
A second inline fan may be needed for long runs of ductwork, or for increased air volume.

Add-on module for monitoring of temperature / humidity / CO2 with wifi communication.

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Cheaper standalone air purifiers (like sharperimage products) are about $120.
Cheap HEPA are $230 Blueair 210B HEPASilent™ Air Purifier with Bonus Particle Filter with price quickly going over $440 Blueair HEPASilent™ 510B Air Purifier with Bonus Filter.
HEPA replacement filters retail for around $100.