HEPA is just a standard - a very high one..   It could be met by any
technology.

It's worth adding good quality filters of one type or another to central
heating systems.  If they meet the HEPA standard or another similarly high
standard, so much the better.....

One easy way is to put 3M Filtrete filters on the intakes....

Hello,
You need both:
The Hepa catches and holds, so the air is recycled threw the dirt.
The electronic with ions cleans and throws much back into the room,
however it all sticks on the walls, furnitute, blinds, fixtuures etc,
much as what you see in your cloths-dryer filter is an example, but of
course a lot finer and less. When you dust, the dust will be pure
white.
Candida is probably your root problem.
Another is the mold, so you need an ozon generator, and  O-Zone
bulbs (you can look them up on the Internet).
The Doc to go to for candida is an "Infectious Disease" specialist,
however you will still need this:
Killing the Fungus:
http://www.mall-net.com/mcs/afung.html
Stuffy Nose:
http://www.drmirkin.com/morehealth/G220.htm
Copper:
http://www.drlwilson.com/Articles/candida.htm
Making Salt Water (or go to the drug store and get "OCEAN"):
http://www.educate-yourself.org/dc/saltwatersolutions.shtml

HEPA, HEPA, HEPA....There are some 'clean-room' type HEPA's called
'hyper-HEPA'. Difference is that 99.9% of all particles > 3 microns (?)
go away vs 99.7%.

Go to allergybuyersclub.com...they have a great comparison chart for
the brands they sell.

Also make sure that your vacuum has HEPA filtration - either the bags
or in the cannister.