Wait - you have a HPWH connected to a hydronic floor system? That's an extremely inappropriate setup - the heatpump on a rheem is probably like ~4000 BTU/hr, and it's pulling the heat from the conditioned space, then you're drawing it off and pumping it back into the space via the floor. If you don't have an air-to-water heatpump and don't want fossil fuels, just use an electric boiler.