Abstract: An improved HVAC air handler and control system adapted for measuring and monitoring operating characteristics, the leakage of supply and return ducts to which it is connected, the infiltration leakage of the building it serves, the blockage of air return paths and the watts drawn and air flow generated by its blower. Leakages are measured by blocking outlets of all supply ducts or all return ducts, opening one side of the air handler to outdoor air, running the air handler blower, and measuring the air flow. Airflow may be measured by opening or closing orifices mounted in plenums attached to the air hander or built into the air handler cabinet, or by varying the speed of the blower motor, in connection with an integrated manometer. Thermostat firmware controls all functions.