Supplementary heat must be controlled in such a manner that it does not engage when the outdoor air temperature is above the balance point temperature of the heat pump, except when supplementary heating is required during a defrost cycle or when emergency heating is required during a refrigeration cycle failure.
If a low ambient temperature compressor cutout option is installed, it must not cut out the compressor at temperatures above -8°C (17°F) in the case of standard ASHPs and -15°C (5°F) in case of cold climate ASHPs.
If thermal balance point used for sizing ASHP, it must not cut out the compressor at temperatures above the thermal balance point temperature.
Any independent thermostats for supplementary heating systems (e.g. baseboards) should be turned down 3-5°C lower than the usual to ensure that the heat pump is the primary heating source.
For constant speed systems with multiple stages of compression and supply air temperature sensor control, supplementary heat shall be controlled in such a manner that it does not engage when the supply air temperature is above 25°C.
If the supplementary heat is provided by a furnace in the case of centrally ducted ASHP systems, the control system should be setup in such a way that both the systems cannot operate simultaneously.
New York State Energy Research and Development Authority (NYSERDA) and Mass Save (Massachusetts) maintain a list of controllers that are compatible with centrally ducted heat pumps and supplementary heating systems, including systems that are compatible with dual fuel heat pump systems.24