Your answer is correct, but remember that if we are heating steam, it is at a much higher temperature differential than a typical heat pump. Good luck getting

Your answer is correct, but remember that if we are heating steam, it is at a much higher temperature differential than a typical heat pump. Good luck getting a COP of 3.5 from room temperature up to steam engine temperature. Steam engines operate at well above 100C. Actually, good luck even finding a heat pump that will operate at those kind of temperatures. There is a huge gap in what is commercially available in high temperature heat pumps for e.g. boiling water. The best example that I am aware of is the EcoCute for water heating. Heat pumps are much more efficient for heating water for domestic use than resistive heating. However, the only ones on the market are fairly expensive. I'd be very interested if someone on HN knew of a better option. I've tried building my own high temperature heat pump to go up to around 300C. It isn't easy, because most refrigerator technology is not designed to operate above 100C, so if you use off-the-shelf parts the seals will go or various temperature limit switches will actuate. Then if you try marrying engine parts to AC parts, you have to make your own high-pressure adapters. Overall, its a great way to burn a lot of dollars and hours in the garage. I've considered just buying a Stirling engine and running it backwards, but I've not yet found one which is designed to be able to run effectively as a heat pump. Any Stirling aficionados here? I'd love some advice on using a Stirling as a heat pump.