Air changes per hour (ACH) is a ventilation metric that measures how frequently indoor air is replaced and filtered within a 60-minute time period. When choosing an air purifier, ACH values can play an important role in determining air cleaning efficiency and filtration power.
Understanding ACH values, metric calculations, and associated symptom relief is key to guarantee maximum air quality protection and fast filtration efficiency within indoor spaces.
What does ACH mean?
Air changes per hour is a metric system utilized to measure how often indoor air particles are cleaned and filtered within one hour in a controlled indoor space, meaning an ACH value of 2 equals to air particles being replaced 2 times in an hour. ACH values commonly range on a scale of 1-6; however, exceptional air quality filtering and ventilation can produce higher ACH levels (1).
For air purifiers, the higher the ACH calculated value, the higher the indication that air particles within a room have been replaced through filter circulation. Low ACH values could determine stagnant air or a lack of proper ventilation in an enclosed space.
Therefore, by calculating ACH levels for air purifiers or air cleaning systems, families and homeowners can gain a better understanding of the air filtration efficiency surrounding them.
How do you measure ACH?
Air changes per hour is calculated through a simple equation combining system airflow in cubic feet per minute (CFM) with timespan divided by the room dimensions. Check product packaging to see manufacturer labeled ACH values or calculate at home through personal measurements. To measure air changes per hour, utilize the equation:
Measuring ACH levels not only allows for an in-depth understanding of the surrounding ventilation and filtration efficiency in a space, but also ensures health symptoms are alleviated and clean air quality is maintained through quantitative data.
Most manufacturers provide ACH only for the highest speed setting. Therefore, it’s important to understand ACH, so that you are aware how to determine ACH on the speed setting that you will use the air purifier. You will need the CFM for each speed setting to determine this. It’s important to have at least two air changes per hour to make an acceptable difference in air quality in a room or space.
What does ACH help with?
Air changes per hour measures differences in air quality and pertain associated benefits with higher ACH values that help alleviate health conditions and symptoms.
According to a recent study, higher ACH levels have been found to be associated with respiratory symptom relief, reduced allergies, and healthier breathing by eliminating infectious aerosols (2). Rooms with high activity may require higher ACH levels to properly address elevated airborne pollutant activity. Contrastingly, large rooms with low activity or occupancy may not require high ACH levels to sufficiently provide clean air ventilation.
The Centers for Disease Control and Prevention (CDC) recommends an ACH level of 7 or higher for the “best” ventilation efficiency, labeling an ACH value of 4 as “good” and a 6 as “better” (3).
Why does ACH matter when choosing an air purifier?
Air changes per hour is an important measurement tool and scale for determining air filtration efficiency, ensuring proper circulation and ventilation is actively cleaning the air. Selecting an air purifier with a high ACH value ensures maximum filtration efficiency while improving health conditions and symptoms. By utilizing ACH values to choose clean air systems, efficient ventilation and filtration power can be guaranteed for indoor spaces.
Individuals with asthma, eczema, and respiratory difficulties also experienced an improvement of symptoms through ACH measurements and stability. Elevated ACH levels can substantially reduce the time to remove airborne pollutants, creating a high-filtration-efficiency environment and limiting exposure to harmful particles.
Check for “Shortcutting” in air purifier design
In air purification, "shortcutting" is an airflow design flaw where an air cleaner's intake and exhaust are too close, causing freshly filtered air to re-enter the machine immediately instead of circulating through the room.
IQAir systems prevents shortcutting by placing intakes and outputs at opposite ends with its Swiss Design and manufacturing.
Understanding Shortcutting:
- The Problem: Poorly designed purifiers pull clean air right back in, wasting energy and reducing effective room cleaning.
- The IQAir Design: Units like the HealthPro series separate intake (bottom) and outflow (top/opposite ends) to force complete room air mixing.
- Result: Maximizes air changes per hour (ACH) without recycling already-purified air.
How to increase ACH levels
Air changes per hour values are not set in stone and are influenced by the actual speed setting being used and if the air purifier is designed to prevent shortcutting. High ACH levels have been linked to allergen symptom relief, the dilution of indoor airborne pollutants, and reduced exposure to harmful particles. ACH levels can be elevated within indoor spaces through additional air cleaning technology and daily ventilation practices, such as:
- Air cleaning technology: Utilize multiple HyperHEPA air purifiers in high activity spaces, rely on HVAC filtration to increase airflow, and install an air quality monitor to know when outdoor ventilation is safe
- Daily practices: Open windows during periods of low outdoor activity, employ fans to increase air circulation throughout rooms, and routinely clean surfaces to limit airborne pollutants
Employing additional air quality metrics could help further contextualize the filtration and ventilation efficiency within indoor air, such as CADR and CCM. The Clean Air Delivery Rate (CADR) measures how fast an air purifier can produce clean air, while Cumulative Clean Mass (CCM) determines how much pollutants an air purifier can capture before losing efficiency.
Frequently Asked Questions (FAQs)
Is ACH important?
Yes, air changes per hour (ACH) is an important metric system for determining clean air ventilation and filtration efficiency. ACH measures how often an air cleaning system can clean and replace the air particles in a room. Specific ACH values detail how efficiently and effectively an air purifier system functions within the hour timeframe.
By quantifying performance results, the air purifier selection process is simplified and ensures the most optimal decision can be made.
Where can I find my ACH level?
Check the air cleaning device’s product packaging for a listed ACH value or ranking. If no ACH value is listed, utilize the ACH equation to calculate at home and determine a device’s ventilation efficiency.
What does ACH stand for?
ACH is an acronym for air changes per hour, meaning this metric measures how many times air particles can be replaced within an hour in an indoor space.
How do CCM and CADR relate to ACH?
Cumulative Clean Mass (CCM), Clean Air Delivery Rate (CADR), and Air Changes per Hour (ACH) are all metrics measuring specific aspects of clean air quality, such as ventilation, filtration, and healthy particle production. These metrics help quantify air purifier capabilities to find the best air cleaning results through proven data collection.
Employ CCM, CADR, and ACH calculations to ensure maximum pollutant protection and filtration efficiency is achieved between every air cleaning device.
Conclusion
Air changes per hour (ACH) is an essential metric tool that allows us to understand ventilation efficiency, symptom relief, and clean air filtration through quantitative, tangible data values and levels. Without understanding ACH, health risks and invisible pollutants may unknowingly prevail within indoor spaces.
Employ clean air technology and filtration practices to achieve high ACH levels for maximum ventilation efficiency and harmful pollutant reduction.
