With an exterior storage tank, I'm sure you could work something out. I could still pull hot water from my boiler as I just installed valves instead of cutting the lines. That said, it does have a 30W conventional resistance coil for high demand times. We had my family (wife, 2 smaller kids, and my parents in law for a week). The tank did switch to normal resistive heating once in a while, but we never had water that was cooler than expected. Now that they have gone, I've forced it into heat pump mode only. No problems so far.