Ford Edge 2016 Owner's Manual page 158

Starting and Stopping the Engine
The heater uses 0.4 to 1.0 kilowatt-hours
of energy per hour of use. The system does
not have a thermostat. It achieves
maximum temperature after
approximately three hours of operation.
Using the heater longer than three hours
does not improve system performance and
unnecessarily uses electricity.
155
Edge/Galaxy/S-MAX (CDQ) Canada/United States of America, enUSA, First Printing