Common Questions
Air Purifier Buying FAQ
What is CADR and why does it matter?
CADR stands for Clean Air Delivery Rate — it measures how quickly an air purifier removes pollutants from the air, expressed in cubic feet per minute (CFM). A higher CADR means the unit cleans air faster. For a room, you want a CADR rating that allows the purifier to cycle the room's air at least 4–5 times per hour. The CADR is tested independently by AHAM (Association of Home Appliance Manufacturers) and is the most reliable spec to compare across brands.
What's the difference between HEPA and True HEPA?
True HEPA filters capture 99.97% of particles 0.3 microns and larger — this includes dust, pollen, mold spores, pet dander, and most bacteria. Regular "HEPA-type" or "HEPA-like" filters are not the same — they may only capture 85–99% of particles and are often used to cut manufacturing costs. Always look for "True HEPA" or "H13 HEPA" on the label. If you have allergies or asthma, True HEPA is non-negotiable.
Do I need activated carbon for odors?
Yes — HEPA filters capture particles but do nothing for gases, odors, or VOCs (volatile organic compounds from paint, cleaning products, furniture off-gassing). Activated carbon adsorbs these molecules. If you have pets, cook frequently, live near traffic, or are sensitive to smells, look for a purifier with a thick activated carbon layer — not just a thin carbon coating on the pre-filter, which is largely ineffective.
How often do I need to replace filters?
Pre-filters every 2–3 months (or wash if washable). True HEPA filters every 12–18 months. Activated carbon filters every 6–12 months depending on odor load. Always check the manufacturer's recommendation for your specific model. Running a purifier with a clogged filter is worse than no purifier — it restricts airflow and can actually recirculate pollutants. Factor filter replacement cost into your total budget before buying.
Should I run my air purifier 24/7?
Yes, for best results. Air quality degrades quickly once a purifier stops — pollutants, dander, and dust re-settle within minutes to hours. Most modern purifiers are designed for continuous operation and use very little electricity on low or auto settings ($20–$50/year). Set it to auto mode so the fan speed adjusts based on detected air quality. Running 24/7 on low uses less electricity than running on high for a few hours.
Where should I place the air purifier in a room?
Place it where airflow is unrestricted — away from walls, corners, and furniture. The ideal position is near the source of pollutants (near a pet bed, cooking area, or doorway). In a bedroom, place it at least 2 feet from the bed for white noise comfort while still cleaning the breathing zone. Elevating it slightly (on a nightstand or shelf) helps it reach airborne particles more efficiently. Never place it behind furniture or in a closet.
Is one large unit better than two smaller ones?
For a single room, one correctly-sized unit is usually better — it's more energy efficient and easier to maintain. Two smaller units make sense for large open-plan spaces where one unit can't circulate air to every corner, or if you want to move units between rooms. If your space is over 600 sq ft with a standard ceiling, consider either a high-capacity single unit or two mid-range units placed strategically on opposite ends of the room.