The rate at which air is exchanged (in the premises) represents another method of measuring ventilation capacity & effectiveness. Air exchange rate is typically expressed in Air Changes per Hour – “ACH”. Air changes per hour can be estimated by determining the total air supplied to, and removed from, the premises “total air exchange” or the outdoor (fresh) air supplied to, and removed from, the premises “outdoor air exchange”. We invite you to experience how this calculator can transform your workflow. Whether you’re specifying a new system, troubleshooting an existing installation, or teaching the next generation of HVAC professionals, this tool was built with your needs in mind.