Iheat Electric Tankless Water Heater Model AHS21-D Runs 1 to 1.5 showers at 1 time in regions where the incoming water is above 45F Capacity of heating 4 GPM at a 35 degree F degree temperature rise. Runs 2 to 3 showers at 1 time in regions where the incoming water is no lower than 65F Continuously monitors all real time data collected 60 times a second For applications as Floor heating, multiple units in series, and recirculating configurations