Instant-Flow SR-Low Flow 0.35 GPM Point of Use Electric Tankless Water Heater, 15 Amp, 120-Volt, 1800-Watt

A:  Same issue here? all I want to do is warm the very cold water at one sink until the hot water arrives. Not enough room to add a small tank water heater or bigger circuit. After reading a few of these answers here it seems that this unit has no use at all

A:  This particular product would not work in the application you describe. At 1800 Watts, its capacity is only 6143 BTU's which will not significantly heat any quantity of water. Also this unit would restrict the flow of water to your entire bath to .35 Gallons per Minute, which will not be enough. However your logic is spot on. Many times small point of use water heaters will be used as buffer storage to provide immediate hot water. You want to select one that has actual hot water storage and will allow full volume of water to pass through it, when the hot water supply does arrive. As putting a small tank type point of use water heater at the point of use, may not be practical you may want to consider installing a water recirculation system instead. It will send the cooled hot water back to the water heater, through the cold line. thus insuring there is always hot water at the bathroom. An example would be the "Grundfos 595916" if you put that in the search box, on the Home Depot site it will come up.

A:  If you look at the specification sheet, a PDF of which can be found under the header info and guides, on the Home Depot product listing page, you will find that this unit can raise the temperature of .41 gallons of water per minute 31 degrees. As most shower heads are three gallons per minute plus, I would say absolutely not. Not only will not heat nearly enough water but it won't raise the temperature enough. Calculating the required capacity is a straight math problem. You just need to know the incoming temperature of the cold water and how many gallons per minute you want to produce. With this information the kilowatt capacity needed can be determined. In all but extremely warm climates this typically exceeds the electrical service to the home. This is why water heaters have tanks so that the water can be heated over time, as the amount of current needed to heat large quantities of water instantaneously is more than most residential services can handle.

A:  No that is not how this product operates. More conventional tank type hot water heaters would have an aquastat that would shut off the heat source when a high limit is reached. This unit as with most tank type hot water heaters comes on when the flow switch indicates the flow of water. The unit adds a fixed measure of energy to the water. To regulate the output temperature you would either govern the flow rate or install a tempering valve on the output.

A:  Your logic is sound but this is not the product you would use. First the unit will come on whenever there flow and second it does not have enough capacity to do the job. So this is not the product. However I have seen this done with a small tank type hot water heater. The small amount of storage will do the job and when the hot water reaches the tank the aqua-stat will shut off the element.