I am still forming opinions on them at this point. I have installed a few electric instant heaters in office buildings, to provide tenants local hot water for an individual bathroom or for a sink in a lunchroom.Their purpose is to provide continuous hot water for one fixture. In offices, they allow water heating in areas considered hard to get to. Most of them do not require pressure relief valves and the drain attached to same. From a plumbing standpoint, cold water supply is needed only. There is the requirement of bringing in electricty to power them up, ranging from 120, 240 and 270 volts. Sometimes there is not enough panel to power up a quantity of these devices.The gas units require a chimney, which adds additional costs.For most multi bath homes in the US, using a standard or larger than standard water heater, (gas preferred) provides the ability to get a good sized family out the door quickly in the morningGas water heaters on average, heat water for $180 per year.I will be adding more links for the instant water heaters on the water heater page located at: http://www.terrylove.com/wh.htmRegards, Terry