According to Autotherm, their T-2500 Energy Recovery System (ERS) is the least expensive (less than $750), smallest and lightest (5 lbs.), easiest to install system in the no-idle industry. By adding a small pump in the water line of the engine and by taking control of the vehicle HVAC system thru the ERS's Central Control Unit, the cab heater can operate fully with the ignition off and keep the cab warm for up to 4 1/2 hrs. The System also provides cab ventilation in the summer and Controlled Engine Cool Down all year round.