sensor unit can be secured to the heat exchanger 33 in a multitude of ways such as by a section of adhesive tape which can also be thermally conductive in nature as with copper of aluminum foil tape to aid heat flow in operation thermal energy flow is monitored by the formula q k t1 t2 where q is the energy flow amount k is a constant depending upon the heat exchanger characteristics and the thermal conductivity of sensor element 34 and t1 t2 is the difference in temperature between the two major sides of sensor element 34 as measured by temperature sensors 35 and 36 fig5 illustrates two further applications of said energy monitoring circuit a typical space conditioning heat exchanger unit 79 consists of a heat exchanger 85 a fluid supply pipe 88 a fluid return pipe 89 an air moving blower fan 87 and a blower motor 86 temperature sensors 81 and 82 are exposed to the airflow over the heat exchanger 85 from blower fan 87 and correspond respectively to temperature sensors 35 and 36 of fig2 being electrically coupled to said energy monitoring circuit via leads 83 and 84 sensor 81 is exposed to the output airflow to heat exchanger 85 and sensor 82 is exposed to the input airflow to heat exchanger 85 the difference in temperature of the air flowing over heat exchanger 85 is proportional to the thermal energy transferred to or from said unit variations in airflow rates from blower 87 can be.