now to fig6 there is shown the operational characteristics of a heat recovery apparatus equipped induction motor which is connected to a source of ac supply with significant phase delay 720 as a result of thermal inertia of the motor mass and the heat removed by the heat recovery apparatus the motor absolute temperature slowly rises until it reaches thermal equilibrium 730 the increased efficiency of a heat recovery apparatus will result in an absolute motor operating temperature below the design limit 740 even though motor operational efficiency has been reduced as a result of the phase delay described above referring now to fig7 there is shown a schematic fragment of one preferred embodiment of an apparatus which is capable of introducing a phase delay in the ac mains supply voltage a source ac mains supply voltage 600 is applied to low voltage power supply 630 and one supply lead of a permanent capacitor induction motor 610 a permanent capacitor motor is preferred as the construction of the motor will allow operation on a phase delayed source of ac supply without modification other types of motors such as split phase designs may not operate on such an apparatus the second supply lead of motor 610 is connected to a semiconductor alternating current switch 620 which is preferably a triac a zero crossing detect.