1. What is ACH (Air Changes per Hour)?

Definition: ACH measures how many times the air in a space is completely replaced with fresh air in one hour.

Purpose: It's a crucial metric for HVAC design, indoor air quality assessment, and ventilation system evaluation.

2. How Does the ACH Calculator Work?

The calculator uses the formula:

Where:

• \( ACH \) — Air changes per hour
• \( Ventilation\ Rate \) — Air flow rate in cubic feet per minute (cfm)
• \( Volume \) — Space volume in cubic feet (ft³)

Explanation: The ventilation rate (cfm) is converted to cubic feet per hour (×60) then divided by room volume to determine complete air changes per hour.

3. Importance of ACH Calculation

Details: Proper ACH ensures adequate ventilation for occupant health, controls contaminants, and maintains comfortable indoor environments.

4. Using the Calculator

Tips: Enter the ventilation rate in cfm and room volume in cubic feet. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical ACH for different spaces?
A: Homes: 0.35-1 ACH, Offices: 2-4 ACH, Hospitals: 6-12 ACH, Labs: 6-15 ACH depending on use.

Q2: How do I find my ventilation rate?
A: Check HVAC specifications or measure airflow at vents using an anemometer.

Q3: What if my space has multiple ventilation rates?
A: Sum all supply or exhaust rates (whichever is larger) for total ventilation rate.

Q4: How do I calculate room volume?
A: Multiply length × width × height of the space in feet.

Q5: What's the 60 in the formula for?
A: It converts minutes to hours (60 minutes/hour) since ACH is per hour but cfm is per minute.