 Manufacturers include Mitsubishi and Fujitsu.One Mitsubishi model provides heat at −35 °C, but the Coefficient of performance (COP) drops to 0.9, indicating that resistance heating would be more efficient at that temperature.At −30 °C, the COP is 1.1, according to the manufacturer's data, although the manufacturer's marketing literature also claims a minimum COP of 1.4 and performance to −30 °C.