Our Summer has arrived in a hurry, and residential cooling systems are starting to get a thorough work out. Evaluating the performance of an air conditioning system is fairly simple when you know what to look for. As a home inspector, one of the key evaluation points that we can check is called Temperature Differential, of Delta T, but exactly what is the Temperature Differential....

True or False? The Temperature Differential or Delta T of an air conditioning system measures change in air temperature between the incoming (return) air and outgoing (supply) air.

TRUE - The Temperature Differential or Delta T is the measurement of the temperature change between the air entering the HVAC system (usually from a return air grill) and the air exiting the air handler (usually measured at the point closest to the air handler unit or what is you might call the "inside" air conditioner unit). The acceptable allowance is a range of 14 to 21 degrees. If the measurement is less than 14 degrees, it typically indicates the system is not cooling properly. A measurement greater than 21 degrees typically indicates there is blockage at the return compartment and air is not properly flowing over the cooling coils (A-coil). This condition is most likely a badly clogged filter or contaminated A-coil, and the system needs to be serviced to restore functionality between the standard 14 to 21 degrees.

Rebekah Haraczka of 100% Realty, Inc.