On 2008-03-17, S. Barker wrote:

There's NO WAY you can get 140 degree water from 39 degree input
with a tankless.

That's simply false. The burner's firing rate is modulated based on
the flow rate and the needed temperature rise to provide the set
temperature.

Admittedly, a tankless water heater will be somewhat taxed by cold
incoming water. For example, the Noritz N-0631 has a maximum input
rate of 180,000 BTUs/hr and can achieve a 3.0 gpm flow rate at 100
degree F temperature rise. So that's just enough for two 2.0 gpm
showers simultaneously (since in a shower you will mix it down to 110
degree water).

Cheers, Wayne