 At colder outdoor temperatures the heat pump is less efficient; it could be switched off and the premises heated using only supplemental heat (or emergency heat) if the supplemental heating system is large enough.There are specially designed heat pumps that, while giving up some performance in cooling mode, will provide useful heat extraction to even lower outdoor temperatures.An air source heat pump designed specifically for very cold climates can extract useful heat from ambient air as cold −30 °C (−22 °F).