Heat Pumps should have a method to turn the condenser off when the heat pump reaches the tipping point and stops being able to produce effective heat for indoor comfort factors. Many heat pumps are installed without this method to turn it off when it reaches this tipping point of ineffectiveness. There are two methods that can easily turn the heat pump off when it reaches the tipping point described. One is to have an outdoor thermostat that will turn the heat pump condenser off when it reaches the tipping point. The other method is to use an indoor thermostat that reads the outside temperature and allow the indoor thermostat to control the heat pump condenser based on the outside temperature. The Honeywell VisionPro heat pump thermostat has this ability. Two terminals in the Honeywell VisionPro are used for remote temperature sensing. It does require running a an additional shielded wire to the remote solid state temperature sensor (thermistor) but it is far more reliable and easier to control through the thermostat than it is from an outdoor thermostat hooked up to the heat pump condenser. Plus, if it is set up properly you will be able to visually see the temperature outdoors from you thermostat. The Honeywell VisionPro has in its display a reading for outdoor air temperature if the outdoor air temperature sensor is hooked up. The real bonus to have the heat pump condenser shut down when it reaches the tipping point is that you will save energy because you do not have the run the heat pump condenser when it is not doing anything. This is why heat pumps are installed in geographical climate zones where the air temperature rarely falls below 38° F.