Thermostats used on heat pumps vary significantly, but most have an setting to turn the entire system off and a setting to set the heat pump to create hot or cold air. They also have a setting for emergency heating.
Thermostats allow operators to select their desired temperature. Often, the "heat" and "cool" mode store the value used most recently, allowing users to avoid changing the temperature too often. As with all heating and cooling systems, heat pumps operate most effectively when the temperature setting is left unchanged for periods of time, so some programmable thermostats can be counterproductive. However, heat pumps are better able to handle changes than gas- and oil-powered systems.
Most heat pumps also have an emergency setting, sometimes marked as "em heat," for use when the system cannot create warm air quickly enough or if the heat pump itself has failed. This setting relies on electrical resistance to generate heat and operates inefficiently. Avoiding this setting allows users to save a significant amount of money.
Depending on the design of the heat pump, a programmable thermostat may set the heat pump into an emergency mode, leading to high electricity bills. As a result, experts recommend using a programmable thermostat designed for use with heat pumps or using a traditional thermostat instead.