hi all,

can I know where can I get maintenance free air purifiers? means no need to change filter.

The main purpose of air purifier is to trap contaminants, if one's doesn't require to replace filter, where are those contaminants going?
All air purifier need to replace filters.

But still can’t imagine my hepa filter (according to user manual to change every two years) could last without doing anything to it. On 24hrs per day.

Mind to show what air purifier doesn't need filter change? Ionizer doesn't really fall in air purifier category, it only traps contaminants in the air and fall to the ground, which the contaminants are still there.

If you are really looking for an air purifier, best to check for 3rd party certification. Many air purifiers don't even meet HEPA requirements (0.3 micron and able remove 99.99% particles, not 99%) but they showing their filters are HEPA standard. CADR & coverage area also might be misleading by the company. Example as below, advertised coverage area is whooping 2650 sqft (almost a luxurious condo unit size) but as tested by AHAM is 695 sqft (4 times smaller).

Atmosphere air purifier from Amway
https://www.allergyuk.org/get-help/products...re-air-purifier

What's the purpose you bought the air purifier?