What is a good CADR rating for an air purifier?

A good CADR rating depends on your room size. For a 300 sq ft room, look for a CADR of at least 200 CFM for smoke, 210 for dust, and 230 for pollen. Higher CADR means faster air cleaning. Always match the CADR to your room's square footage.

Do I need a HEPA filter or can I use a carbon filter alone?

For capturing particles like dust, pollen, and pet dander, a HEPA filter is essential. Carbon filters are best for removing odors, gases, and VOCs. For comprehensive air purification, choose a unit with both HEPA and carbon filters. UV filters can add germicidal benefits but are not a replacement for HEPA.

How loud is an air purifier typically?

Noise levels vary by model and fan speed. Most air purifiers range from 20 dB (whisper quiet) on low to 60 dB (conversation level) on high. For bedrooms, look for units with a sleep mode below 30 dB. Check the product specifications for decibel ratings.

Air Purifier Buying Guide: How to Choose the Right One

Choosing the right air purifier can feel overwhelming with so many technical terms like CADR, HEPA, and UV. Our editorial team compared specifications, buyer feedback and key decision factors to create this comprehensive guide. Whether you need relief from allergies, want to remove pet dander, or just want cleaner air, this guide will help you make an informed decision.

Understanding CADR: The Key Performance Metric

CADR stands for Clean Air Delivery Rate, a standard developed by the Association of Home Appliance Manufacturers (AHAM). It measures the volume of filtered air an air purifier delivers per minute, expressed in cubic feet per minute (CFM). There are three separate CADR ratings: for smoke, dust, and pollen. Higher numbers indicate faster filtration.

To effectively clean a room, the CADR for smoke should be at least two-thirds of the room's square footage. For example, a 300 sq ft room needs a smoke CADR of 200 CFM or higher. Always check the CADR ratings on the product or its AHAM certification. A higher CADR means the unit can clean the air more quickly, but it may also be louder and use more energy.

Filter Types: HEPA, Carbon, UV and More

HEPA Filters

True HEPA filters are the gold standard for particle removal. They capture at least 99.97% of particles as small as 0.3 microns, including dust, pollen, mold spores, and pet dander. For allergy sufferers, a HEPA filter is essential. Some units advertise "HEPA-type" or "HEPA-like" filters; these are not certified and may be less effective. Always look for "True HEPA" certification.

Activated Carbon Filters

Activated carbon filters are designed to adsorb gases, odors, and volatile organic compounds (VOCs). They are excellent for removing smoke, cooking smells, and chemical fumes. Carbon filters are not effective against particles; they work best in combination with a HEPA filter. The amount of carbon (measured in pounds) affects how long the filter lasts and how well it adsorbs pollutants.

UV (Ultraviolet) Filters

UV air purifiers use ultraviolet light to kill bacteria, viruses, and mold spores. However, UV light alone does not remove particles or gases. For UV to be effective, the air must be exposed to the light for a sufficient time, which is often not the case in portable units. Many experts recommend HEPA filtration over UV for general air cleaning. Some units combine UV with HEPA and carbon for a multi-stage approach.

Other Filter Types

Some purifiers include pre-filters to capture large particles like hair and dust, extending the life of the main filter. Electrostatic precipitators use an electrical charge to attract particles, but they can produce ozone, which is a lung irritant. Ionizers also generate ozone; the California Air Resources Board recommends avoiding ionizers that produce ozone. Always check for ozone-free certification.

Room Size Matching: How to Calculate the Right Capacity

Matching the air purifier to your room size is crucial for effectiveness. Manufacturers typically specify a maximum room size, but this is often based on an ideal scenario with low ceilings and minimal obstructions. A more reliable method is to use the CADR rating.

Measure your room's length and width in feet to get the square footage (e.g., 12 ft x 15 ft = 180 sq ft).
For standard 8-foot ceilings, the recommended CADR for smoke should be at least two-thirds of the square footage (e.g., 180 sq ft x 2/3 = 120 CFM).
If you have high ceilings (over 8 ft), increase the CADR proportionally. For a 10 ft ceiling, multiply the square footage by 1.25.
For rooms with heavy pollution (e.g., smokers, pet dander), choose a unit with a CADR 50% higher than the minimum recommendation.
Consider placing the purifier in the room where you spend the most time, such as the bedroom or living room. For whole-house coverage, you may need multiple units.

Noise Levels and Energy Consumption

Noise Levels

Air purifiers produce noise from the fan and air movement. Noise is measured in decibels (dB). A whisper is around 20 dB, a quiet library is 40 dB, and normal conversation is 60 dB. Most purifiers have multiple fan speeds; lower speeds are quieter but clean slower. For bedrooms, look for a sleep mode that operates below 30 dB. Check the product specifications for noise levels at each speed. Some units are specifically designed to be ultra-quiet.

Energy Consumption

Air purifiers run continuously, so energy efficiency matters. Look for an Energy Star certified model, which uses about 40% less energy than standard models. The power consumption is measured in watts. A typical purifier uses between 20 and 100 watts on high speed, similar to a light bulb. Running a 50-watt unit 24/7 costs roughly $5 to $10 per month, depending on your electricity rate. Energy Star models often have efficient motors and smart features like auto mode that adjusts fan speed based on air quality.