Home Air Quality Risk Estimator
Our ai enhanced tool computes home air quality risk accurately. Enter your inputs for detailed analysis and optimization tips.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
Indoor AQI = Outdoor AQI x Infiltration x Ventilation x Purifier + Indoor Sources
Indoor AQI is calculated by combining outdoor pollutant infiltration (based on building envelope tightness, ventilation type, and purifier effectiveness) with indoor-generated pollutants (from occupants, cooking, and household sources). Each factor reduces or contributes to the total indoor air quality index.
Worked Examples
Example 1: Urban Apartment with Moderate Outdoor Pollution
Problem:A 15-year-old apartment with outdoor AQI of 85, natural ventilation, 4 occupants, no air purifier. Estimate indoor air quality.
Solution:Infiltration rate for 15yo building: 0.50. Ventilation multiplier (natural): 1.0. No purifier reduction. Outdoor contribution: 85 x 0.50 x 1.0 x 1.0 = 42.5. Occupant contribution: 4 x 8 = 32. Household: 15. Indoor generated: (32 + 15) x 1.0 = 47. Total indoor AQI: 42.5 + 47 = 90. PM2.5: ~27.5 ug/m3 (exceeds WHO guideline by 5.5x).
Result:Indoor AQI: 90 (Moderate) | PM2.5: 27.5 ug/m3 | CO2: ~1,420 ppm — needs ventilation
Example 2: New Home with HEPA Purifier
Problem:A 3-year-old home with outdoor AQI of 120 (wildfire smoke), HRV ventilation, 2 occupants, HEPA purifier running.
Solution:Infiltration rate for 3yo: 0.30. HRV multiplier: 0.40. HEPA reduction: 0.40. Outdoor: 120 x 0.30 x 0.40 x 0.40 = 5.8. Occupant: 2 x 8 = 16. Household: 15. Indoor generated: (16 + 15) x 0.40 = 12.4. Total: 5.8 + 12.4 = 18. Despite unhealthy outdoor air, indoor AQI is Good. PM2.5: ~4.3 ug/m3 (within WHO guideline).
Result:Indoor AQI: 18 (Good) | PM2.5: 4.3 ug/m3 | 85% reduction from outdoor levels
Frequently Asked Questions
Is indoor air quality really worse than outdoor?
The EPA estimates that indoor air can be 2-5 times more polluted than outdoor air, and in some cases up to 100 times worse. This is because indoor environments concentrate pollutants from multiple sources: cooking (PM2.5, NO2), furniture off-gassing (VOCs, formaldehyde), cleaning products, mold, pet dander, and human bioeffluents. Unlike outdoor air which disperses pollutants over large volumes, indoor air recirculates in enclosed spaces. Americans spend approximately 90% of their time indoors, making indoor air quality arguably more important than outdoor AQI for overall health. Proper ventilation and filtration are essential for maintaining healthy indoor environments.
How does home age affect indoor air quality?
Home age affects air quality in two competing ways. Older homes (pre-1990) tend to have leakier building envelopes with higher natural infiltration rates, meaning outdoor pollutants enter more freely but indoor-generated pollutants are also diluted faster. Newer homes (post-2000) are built much tighter for energy efficiency, which reduces outdoor infiltration but can trap indoor pollutants if not properly ventilated. Very new homes also have higher VOC levels from new construction materials, paint, and furniture. The sweet spot is a well-sealed home with mechanical ventilation and filtration, which controls both outdoor infiltration and indoor buildup.
How effective are HEPA air purifiers for indoor air quality?
HEPA air purifiers are highly effective for particulate matter, capturing 99.97% of particles 0.3 microns and larger. In real-world home use, a properly sized HEPA purifier can reduce PM2.5 levels by 40-60% in the room where it operates. However, effectiveness depends on several factors: the unit must be sized for the room (look for CADR rating matching room size), filters must be replaced regularly (typically every 6-12 months), and doors/windows should remain closed. HEPA purifiers do not remove gases like CO2, VOCs, or radon. For comprehensive air quality improvement, combine HEPA filtration with adequate ventilation and source control (reducing pollutant generation).
Should I keep windows open or closed for better air quality?
The answer depends on your outdoor AQI. When outdoor AQI is below 50 (Good), opening windows provides beneficial ventilation that dilutes indoor pollutants and replenishes oxygen. When outdoor AQI is 50-100, balance is needed — brief airing during low-traffic hours (early morning) is acceptable. When AQI exceeds 100, keep windows closed and rely on mechanical filtration. During wildfire smoke events (AQI 150+), sealing the home and running HEPA purifiers is essential. A compromise solution is a heat recovery ventilator (HRV) with MERV-13+ filters, which provides continuous fresh air while filtering outdoor pollutants. Season also matters — pollen counts affect the optimal window strategy for allergy sufferers.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy