A healthy and consistently comfortable indoor environment depends on a balanced air exchange rate. HVAC system airflow is always entering rooms through supply vents and being removed from rooms through return vents. The air exchange rate expresses the number of times per hour that the entire air volume in a given room is removed and replaced by fresh incoming air.
How Much Is Enough?
When air exchange is too low, the room environment stagnates and airborne pollutant levels rise. The give-and-take of air exchange must be equalized to ensure optimum air quality and consistent temperature control. What’s acceptable depends on the size of the room, typical number of occupants and general activity level. A single-occupant bedroom, for example, might require 6 air changes per hour to meet standards. However, a lively family room with multiple occupants might need 8 or 10 air changes to stay fresh, healthy and comfortable.
Calculating Air Exchange
To accurately determine the present air exchange rate in a room, an HVAC service technician will measure airflow entering the room through the supply vent. This amount, expressed in cubic feet per minute (CFM), is multiplied by 60 times per minute and then divided by the total air volume of the room (length x width x height.) The result of the calculation is the current air exchange rate for that specific room.
Restoring Proper Air Exchange
Several factors may impair air exchange:
- A dirty or clogged system air filter generally reduces air exchange throughout the entire house.
- An “unbalanced” system may deliver too much air volume to rooms closest to the system blower and too little to rooms furthest away. A qualified HVAC service technician can balance airflow by adjusting damper doors inside ductwork for more even air distribution.
- Issues with system ductwork also impact air exchange. Over time, supply ducts may leak excessive air volume or ducts may become disconnected or collapse. A ductwork pressure test can reveal duct problems. Options like duct sealing and other repairs are available.
For more information about restoring optimum air exchange rate, contact the professionals at Cool Power.
Our goal is to help educate our customers in Hauppauge, New York and the Long Island 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 631-292-0629.