Can I Use a HEPA Furnace Filter?
A HEPA filter uses a dense filtration material and must remove at least 99.7% of airborne particles that are 0.3 microns or larger. This level of filtration is much better than a standard pleated or fiberglass filter.
Unfortunately, HEPA filters restrict too much air to be used as a traditional furnace filter. A HEPA filter is extremely efficient, but a significant amount of air pressure is needed to force air through a HEPA filter. A typical HVAC system will not be equipped to provide enough air pressure to use a HEPA filter (which means that no air would blow out of your registers).
In order to use a HEPA filter for whole house filtration, you need to install a separate HEPA filtration system. A system like this will pull some of the air out of the regular air flow through your furnace, and then boost the air and pass it through a HEPA filter. The extremely filtered air is then returned back into the normal air flow.