[chopper]

Yes, it's natural gas. I don't know of anyone who makes an electric whole-house unit, although I suppose it's possible, but I was told it would take close to 100 amps of power to run it at the same capacity as a gas unit. Rinnai also makes a propane model, if you don't have a gas line to your house.

If you are looking at a point-of-use installation, such as for a dishwasher or upstairs shower, a smaller electric unit may fit the bill. A common installation these days seems to be for dishwasher replacements. The new dishwashers do not heat the same way the older models did. That is, the older models would take water in and heat it to a preset temperature, usually 145 degrees F. The newer units, to make the EnergyStar ratings, have smaller wattage heaters and will only heat up for a maximum of 20 minutes, with a temperature rise of about a degree per minute. Since the dishwasher needs a minimum water temp of 145 deg F to wash properly, that means the water in the bottom of the dishwasher at the start of the cycle has to be at least 125 deg F and is usually specified as such in the installation manual. Even if you have your water heater set to 140 deg F, the line temperature loss transporting the heated water to the dishwasher, plus the temperature loss from the water contacting the dishwasher pan upon entry, pretty much ensures the water temp in the dishwasher cycle will be insufficient to clean the dishes properly. As far as I know, only the Bosch units still use an internal heater that heats to a preset temp; mine heats to 151 deg F according to the literature. Anyway, some folks have taken to installing small electric under-the-sink tankless heaters to feed just the dishwasher and kitchen sink in order to alleviate the dishwasher problem. Bear in mind, however, that even a small under-the-sink electric unit may require 240 volts to operate.