The number of MODEL 1s and their respective power levels required to get enough hot water are primarily driven by two factors; the incoming water temperature, and what flow rate in gallons per minute (GPM) you want.. The easy proxy for flow rate is how many showers you would want to take at a time. Typical shower heads are 2 GPM, with some very good ones now available at 1.5 GPM (for lots of reasons, we love low flow shower heads!) .
The MODEL 1 provides incremental heat to the incoming water, therefore raising the temperature. In order to calculate the temperature rise at 1 GPM, multiply the kilowatts available (which is volts times amps/1000) times 6.83. For example, 240 volts at 48 amps = 11.52 kW, which will provide a 78 degree (F) temperature rise at 1 GPM, or 53 degrees at 1.5 GPM.
The average comfortable shower temperature is about 105 degrees, so if your incoming water temperature is 53 degrees or more, one unit should work for one shower at a time with a 1.5 GPM shower head. If the incoming water temperature is less, or the flow rate is more, you will likely need more than one. Since much of this is site-specific, please click on this link and look at the chart for your groundwater temperature, or contact us for sizing information.