How to Identify Central Heating Air Flow

Air flow is the lifeblood of central heating and many performance, energy efficiency and even indoor air quality issues are either the cause or result of incorrect air flow. Proper air flow results from a correct match between the output of the furnace blower and the size and layout of ductwork that disperses heat throughout the home.

A Question of Balance

Forced-air central heating systems are closed-loop designs integrating separate supply and return ductwork to recirculate air. The supply half of the system conveys heated air from the furnace through ductwork into individual rooms. Simultaneously, the system draws air out of each room into the return ductwork and conveys it back to the furnace for reheating. Equivalent volumes of supply air and return air create neutral air pressure in rooms. This means the system is “balanced,” the optimum condition for efficient heating.

Not Too Much, Not Too Little

The use of industry-standard load calculation software determines the BTUs of heat energy the system must deliver to each room to maintain a comfortable temperature. This data is then used to calculate the cubic feet-per-minute of blower air output as well as the optimum diameter of ductwork to recirculate that air volume efficiently. When imbalances are suspected, a manometer can identify volume at each supply register as well as the air flow through the return duct. Fine tune air flow in and out of each room by adjusting dampers inside the ducts until the room is balanced and neutral air pressure restored.