Why do HEPA air purifiers need replacement filters?
I’ve been able to find Ionic air purifiers that don’t need replacement filters, but I have not been able to find a HEPA air purifier that does not need a replacement filter. Not only do they require replacing the filter but the filters are very expensive.

Here’s some checks of proof ( Click back then go on http://www.100wgezi.com to get started)
hepa is the short name for “high efficiency particulate absorbing”. You are comparing apples to oranges
The reason why you can find Ionic air purifiers that don’t need replacement filters is because they work in a different way from hepa filters. Ionic purifiers charge particles in the air such as dust or pollen and then those particles pass over metal plates with the opposite charge. The air particles stick to the plates like two magnets stuck together. From there, you wash the plates periodically.
These are quiet and easy to maintain, but they don’t have nearly the quality filtration of the HEPA system.
Hepa filters work to trap the dust and particles in the air with cardboard or micro filters. The result is that 99.97% of all particles are trapped. The filters are so expensive because they are designed to capture every tiny particle in the air. If you have allergies, nothing is better for you than a HEPA filter.