If I were you-I would call a local whole saler who sells your brand of heat pump and ask them what thermostat their equipment is designed for. Give them your model and serial number and find out what the recommend. The amperage of the old stat is not necessarily designed to meet system specifications. Most low voltage transformers only handle between 1-3. amps so the thermostat rating should be designed to meet the system amperage not the old stat amps. The manufacturere should be able to help. Why are you replacing your old stat to begin with?