Instant-Flow C-Micro 0.20 GPM Point of Use Electric Tankless Flow Water Heater, 20 Amp, 240-Volt, 4800-Watt, 104°F

A:  The simple answer is ones that produce enough hot water. In reality very few can, and more importantly very few people, if any, have enough electrical capacity to run such a unit if it were available. Allow me to explain the math. I live and practice plumbing here in the North East. Due to our cold winters, resulting in cold incoming water. You need roughly 30,000 BTU's per hour to heat 1 Gallon of hot water instantaneously. As elasticity is 3413 BTU's per Kilowatt, that means you need roughly 10KW of electricity to heat one gallon. So if your washer needs 5 gallons per minute you would need a 50KW heater. As most residential services were not designed and built with that type of a capacity, we make up for that with storage. Your typical 40 gallon water heater has two 4500 Watt elements; but they do not run at the same time. So you heat the water using the 4.5 KW unit. Until the stored water is up to temp and it shuts off. This may take a few hours depending on how cold the water. Then the unit shuts off until there is a water draw. Now some will retort and say that is inefficient. However I don't know why. Tank type hot water heaters are very well insulated and lose very little heat out of there jackets and the heat they do lose is often into heated space. Also by heating the water slowly the draw on the grid is more balanced. My point here is its all math. The amount of water your machines is knowable. As is the temperature rise the water needs. With this info the amount of electricity needed can also be determined. Typically that is beyond the electrical service of the home. I have done installations on commercial ships that have on board generators that make sufficient power to run such units. So they are available. But typically point of use hot water heaters are only used on small draw applications; like infrequent hand washing. If you are in a climate with a warmer supply of cold water possibly this can be done. If you have further questions you are welcome to give me a call. Chris 978 651 3301