When sourcing ceiling air purifiers, prioritize the Clean Air Delivery Rate (CADR), which should be matched to the room volume for at least 5 air changes per hour (ACH). Ensure the unit utilizes H13 or H14 HEPA filters capable of capturing 99.97% of particles down to 0.3 microns. Additionally, check the noise level (dB); for office or classroom environments, the noise should not exceed 45-50 dB at maximum operation. Verify the motor type, as DC brushless motors offer better energy efficiency and a longer lifespan compared to AC motors.