On Thursday, July 9, 2015 at 12:31:55 AM UTC-4, HerHusband wrote:


At this point, you really only have a few options.

1. Return the tankless heater and go back to a tank heater.

2. Replace the tankless heater with a more powerful model.

3. Add a valve to the water line to reduce the flow rate (giving the
heater more time to heat up the water).

Of course, putting low flow aerators on all of your fixtures would help
too.


Agree. Sounds like another satisfied tankless customer. I see
what's going on and how it's annoying, but I'd say the root cause
are the properties of the tankless. It would be solved by having
a tankless sized to maintain constant water temp up to whatever
the max usage rate of the whole house is. But that will likely
take a much larger model, because you have to support the max
reasonable load of the whole house. And if he's having this
problem with just one point of use, it would likely require a much
bigger unit to support two or three simultaneous draws.
Alternative, as you say, is to restrict the hot water flow rate
so that the tankless can keep up. Even then though, I wonder
how variable their burn rate is and if they can actually
maintain a perfectly constant outgoing temp rate? IDK, because
I don't and won't have one, for a variety of reasons, starting
with cost.