- 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