So the term efficiency with heat pumps typically refers to COP Coefficient of Performance. It a measure of how many watts of heat you are able to pump per given

So the term efficiency with heat pumps typically refers to COP Coefficient of Performance. It a measure of how many watts of heat you are able to pump per given watt of electricity used. So 400% would be a COP of 4.0 which is definitely possible with air source heat pumps in milder weather and ground source heat pumps in pretty much any weather.