How do I determine what air purifier I need based on my room size? 
Small rooms, often below 100 sq. Ft, need a table top or mini tower-style air purifier
Medium rooms, between 100 sq. Ft. and 180 sq. Ft. typically need a floor model that has a larger filter 
Large rooms, over 180 sq. Ft, require a full size tower or box style unit. 

What is the difference between True HEPA  and HEPA type?
A True HEPA filter can capture 99.97% of all particles that pass through it that are 0.3 microns or greater in size.
The efficiency of true HEPA is 99.97%,and The efficiency of HEPA type is 90%.

How often do I need to replace my filter?
It should be replaced every 6–8 months depending on use.

What is a carbon filter?
Carbon filters are also called charcoal or activated charcoal/carbon filters.Carbon filters can absorb a variety of chemicals and vapors simultaneously.

What is CADR?
CADR stands for “Clean Air Delivery Rate” which indicates the volume of filtered air delivered by an air purifier. CADR ratings show the effectiveness of how efficient the air purifier is at capturing particles, such as: tobacco smoke , pollens and dust .

How do I know the air quality?
According to the bulb  :  Green —good; Yellow –average ; Red—poor