Electric instantaneous water heater

This is actually more complex that it might appear. The savings on instantaneous heaters is related to the reduction in standby storage losses, and can reduce costs related to piping and other costs. However, there are very specific performance requirements for every model, and some are better than others. There are so many coming into the market, I fully expect some advances in technology and controls, but one thing to consider is "you get what you pay for." If you can get an example, or find one that is installed, take a look.

So, there are two factors that must be commissioned. First, the flow of the lavatory or sink must match the heater. There have been several instances where the aerator does not match the flow requirement, ie too low, and the unit either does not work or the temperature is way too high.

That comes to the second factor, temperature. There are some industry standards, and often the AHJ will have criteria too. Some units are adjustable and control the output to the lav (good) and others are dependent on the flow and cold water temperature, so will not always have a consistent temperature (bad).

If you have one heater with one sink/lav, it is easy, and while a little more first cost, this is my current recommendation based on past experience.

But if you have one heater for multiple outlets, and there are some manufacturers that say they can do this (to reduce costs), the complexity increases dramatically, as does the functional testing. Our experience with this has not been good, either from a design side or a commissioning side.

I do not have 2007 handy, but took a look at 2004. These would fall under Service Water Heating. There are required efficiencies listed for instantaneous water heaters, and they reference National Appliance Energy Conservation Act of 1987. There are required controls for all heaters, and defined temperatures.

So the answer is yes, they must comply with 90.1. I think you should get a copy of the standard and go from there.

That could sure be true, I do not have the standard handy. Basically, electrical heaters are by definition 100% efficient, although there are still standby losses and true conversion of electricity into hot water sure is not 100%. My recommendation would be to focus on the controls, that is what makes or breaks an instantaneous heater.