The air exchange rate in your house tells you important things about the effectiveness of your HVAC system as well as the health of your indoor air quality.
Your heating and cooling system delivers new airflow into rooms through supply ducts while removing air through return ducts. How rapidly the system completely replaces the existing air volume in a room with fresh air is known as the air exchange rate, or air changes per hour (ACH). If the rate for a room is calculated at 7, for example, that means the entire volume of air inside that room is replaced with new air 7 times per hour.
How is Air Exchange Rate Determined?
Using equipment to measure airflow through the supply vent, an HVAC technician can determine the air volume entering a room expressed as CFM (cubic feet per minute). The CFM is multiplied by 60 minutes per hour, then that figure is divided by the total volume of the room—length x width x height. The result is the present air exchange rate for that room.
How Many Air Changes are Enough?
Living spaces have differing recommended ACH rates, depending on the room. For example, to maintain air quality and comfort, a bedroom typically requires 5 to 6 air changes per hour, while a crowded family room or busy kitchen needs more — usually 7 to 8 ACH.
What Causes Insufficient ACH?
When airflow volume into a room doesn't provide the recommended ACH, there may be one or more causes:
- System airflow isn’t properly “balanced.” Some rooms may be receiving excessive air volume while others aren't getting enough. Adjusting internal dampers that control airflow to individual rooms may balance the system.
- System blower is no longer delivering adequate air volume. A worn, defective blower may not move enough air through the ductwork to deliver the recommended air exchange.
- Supply duct issues such as excessive leakage, loose or disconnected segments, and other defects may reduce airflow volume below specs.
To schedule routine maintenance, and a professional examination of the air exchange rate throughout your home, contact Hartman Brothers Heating & Air Conditioning.
Our goal is to help educate our customers in New Haven, Indiana and surrounding Fort Wayne area about energy and home comfort issues (specific to HVAC systems). For more information about other HVAC topics, download our free Home Comfort Guide or call us at 260-376-2961.