Quote Originally Posted by darctangent View Post

I disagree. One tankless would rarely give the same preformance when a contractor thought that two 50's were appropriate. Custom homes usually mean more bathrooms than typical and high end tubs/ multi-head showers, etc. On top of that you are almost certainly not accounting for the reduced BTU capacity that goes with most locations in Colorado, a fatal thing to disregard in this state. That being said, niether of us knows without more information.
It would depend on the BTU capacity of the water heaters. IF they are both 75k BTU units, then I would tend to agree that 1 300k tankless would fall short. However, keep in mind that's it's atill a single family home, and I'm well aware of winter water temps. We hit record lows of 35F incomming water temps here this winter. That still gives you 5gpm at 112F. Plenty to fill a soaking tub and still use a handwash sink. But it might fall short if there was one of those stand-up showers with 20 heads that uses 15gpm. In that case... well in that case, even the 100 gallon storage would run out quick.

A compromise could be to add an electric water heater just as a storage tank and have it just maintain at 120F for hygenic reasons, set the tankless to the same and use a mixing valve to drop it to 115F. IMO there no need to run domestic water over 115F.