# HEPA Air Purifier Guide ## Quick Reference - HEPA Standard: 99.97% efficiency for 0.3 micron particles - Target ACH: 4-6 for allergies, 2-4 for general use - Formula: CADR (m³/h) = Room Volume (m³) × ACH - Power estimate: 0.1-0.5 W per m³/h of CADR > TIP: To achieve optimal air purification, aim for an air purifier with a CADR roughly twice the size of your room. For example, if your room is 25 m², choose a purifier rated for 50 m². This ensures the purifier lasts longer, uses less energy, is less affected by obstacles or poor airflow, and keeps your air consistently cleaner. Always aim for a larger margin than the actual room size. --- ## Why You Need a HEPA Purifier Air purifiers with HEPA filters address several important air quality concerns that affect health and comfort in indoor spaces. Health protection is the primary reason many people invest in HEPA purifiers. These devices capture 99.97% of particles as small as 0.3 microns, which includes most common allergens like pollen, pet dander, dust mites, and mold spores. For people with allergies, asthma, or other respiratory conditions, this can mean fewer symptoms, better sleep, and reduced reliance on medication. HEPA filters also trap many bacteria and viruses, potentially lowering your risk of airborne illness transmission in your home. Indoor air pollution is often worse than outdoor air, sometimes by a factor of two to five times according to EPA estimates. Modern homes are built to be energy-efficient and well-sealed, which unfortunately means pollutants get trapped inside. Cooking releases particulates and gases, furniture and building materials can off-gas volatile organic compounds (VOCs), and everyday activities stir up dust. A HEPA purifier continuously works to remove these particulates from circulation. Smoke and odor removal becomes critical if you live near wildfires, have neighbors who smoke, or cook frequently with high heat. While HEPA filters primarily target particles, many purifiers combine HEPA filtration with activated carbon filters that absorb smoke particles, odors, and some gases. Pet ownership presents specific challenges since animals shed dander, hair, and can track in outdoor allergens. Even people without pet allergies often find their air quality improves noticeably with a HEPA purifier when living with animals. Better sleep and cognitive function can result from cleaner air. Some studies suggest that better air quality correlates with improved sleep quality and cognitive performance, though individual results vary. That said, HEPA purifiers aren't universally necessary. If you live in an area with excellent outdoor air quality, don't have allergies or respiratory issues, have no pets, and your indoor environment doesn't generate much pollution, you might not notice significant benefits. The cost and noise of running a purifier continuously should also factor into your decision. --- ## Air Purifier Sizing & Power Calculation > ⚠️ Warning: Always choose a True HEPA filter. "HEPA-type" or "HEPA-like" filters do not meet the 99.97% efficiency standard and are far less effective. --- ### Step 1: Calculate Room Volume $$\text{Room Volume (m³)} = \text{Length (m)} \times \text{Width (m)} \times \text{Height (m)}$$ Example: 5 m × 4 m × 2.5 m → Volume = 50 m³ Tip: For irregular rooms, break them into rectangular sections and add the volumes together. --- ### Step 2: Determine Air Changes Per Hour (ACH) ACH represents how many times per hour the purifier should completely filter all the air in your room. | Use Case | Recommended ACH | |----------|----------------| | General indoor air quality | 2-4 | | Allergies / asthma | 4-6 | | Smoke / heavy pollution | 6-8 | | Medical/immunocompromised | 8-12 | Choosing your ACH: Start with 4 ACH for most residential applications. Increase to 6 if you have allergies or pets. --- ### Step 3: Calculate Required CADR CADR (Clean Air Delivery Rate) is the metric that tells you how much filtered air the purifier delivers per hour. $$\text{CADR (m³/h)} = \text{Room Volume (m³)} \times \text{ACH}$$ Example: 50 m³ × 4 ACH = 200 m³/h Unit conversion: - 1 m³/h ≈ 0.588 CFM (Cubic Feet per Minute) - 200 m³/h ≈ 118 CFM > Note: Check the purifier's CADR rating for dust/pollen for general purposes, or smoke CADR if dealing with wildfire smoke or cigarette smoke. --- ### Step 4: Estimate Power Consumption $$\text{Power (W)} \approx 0.1\text{-}0.5 \times \text{CADR (m³/h)}$$ Example: CADR = 200 m³/h → Power ≈ 20-100 W Typical power draw by speed: - Low speed: 20-40 W (quiet, good for sleeping) - Medium speed: 40-60 W (balanced performance) - High speed: 60-100 W (maximum filtration) --- ### Step 5: Calculate Energy Costs $$\text{Daily Energy (kWh)} = \frac{\text{Power (W)} \times \text{Hours per day}}{1000}$$ Example: Power = 50 W, running 8 hours/day: $$\text{Energy per day} = \frac{50 \times 8}{1000} = 0.4\text{ kWh/day}$$ Cost calculation (Netherlands ≈ €0.50/kWh): $$\text{Cost per day} = 0.4 \times 0.50 = €0.20$$ - Monthly cost (30 days): €0.20 × 30 ≈ €6.00 - Annual cost: €0.20 × 365 ≈ €73.00 Running 24/7 costs: If running continuously at 50W, multiply by 3 (24h ÷ 8h) → ~€18/month or €219/year --- ## Complete Example Walkthrough Scenario: Living room with allergies, 5m × 4m × 2.5m, run 10 hours daily 1. Volume: 5 × 4 × 2.5 = 50 m³ 2. ACH: Allergies → choose 5 ACH 3. Required CADR: 50 × 5 = 250 m³/h (or ~147 CFM) 4. Estimated power: 250 × 0.3 = 75 W (medium estimate) 5. Daily energy: (75 × 10) ÷ 1000 = 0.75 kWh 6. Daily cost: 0.75 × €0.50 = €0.375 7. Monthly cost: €0.375 × 30 = €11.25 Shopping tip: Look for purifiers with CADR ≥ 250 m³/h. Consider buying one rated slightly higher (300+ m³/h) so it can run on lower, quieter settings. --- ## Additional Tips ### Placement - Position at least 15-30 cm away from walls for proper airflow - Place in the room where you spend the most time - Avoid corners and behind furniture - Keep away from curtains that might block intake ### Maintenance - Pre-filters: Clean monthly (vacuum or rinse) - HEPA filters: Replace every 6-12 months depending on usage - Carbon filters: Replace every 3-6 months - Set calendar reminders for filter checks ### Noise Considerations - dB levels typically range from 20-60 dB depending on speed - For bedrooms, look for models with ≤30 dB on low speed - Most purifiers have a "sleep mode" with reduced noise ### Air Quality Monitors Consider pairing your purifier with an air quality monitor to: - See real-time PM2.5, PM10, and VOC levels - Verify your purifier is working effectively - Adjust settings based on actual air quality --- ## FAQ Q: Can I use a purifier rated for a larger room in a smaller space? A: Yes! This is actually ideal. The purifier will achieve the target ACH while running at lower, quieter speeds. Q: Do I need to run it 24/7? A: Not necessarily. Running during sleeping hours and high-pollution times (cooking, cleaning) provides most benefits. However, continuous operation maintains the most consistent air quality. Q: What about ozone generators or ionizers? A: Avoid ozone generators as ozone is harmful to lungs. Some ionizers are safe but produce trace ozone. Stick with mechanical HEPA filtration for the safest option. Q: Can one purifier handle multiple rooms? A: Only if there's good airflow between rooms and you calculate the combined volume. Generally, one purifier per room is more effective.