One more thing not to forget - water source heat pumps (geothermal) are availible in two stage compressors. The two stage or two speed compressors can greatly increase the heat pumps overall efficiency. They can operate in (think of it as) low, medium or high speed to meet your needs.
Depending on your local earth temperatures, you can see COP's in excess of 5. There is no potential for refrigerant leaks outside, and the tubing is usually guaranteed by the installer for 50+ years. The electricity used for the pumps is typically on the order fo 4 light bulbs (400Watts) only when the heat pump is running.
Your real consideration will be the overall compressor power consumption and the need for emergency backup electric strip heaters. Strip heaters will typically require about 50-70 amp breakers (depending on the size you get, they are optional) and the compressor will typically require about 30-40 amp breakers.
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