I had a Noritz N-069M http://www.noritz.com/n069.html in my newly
constructed
home of about 2500 sqft with 3 1/2 baths. I love it! With no circulation
pump
at all, most hot water locations get hot water within a minute. The only
real
wait time for hot water is the master shower, it takes about 2 minutes. But
the
jetted tub just a few feet from the master shower gets hot water in about 30
seconds.
More water volume to the tub vs. the shower head really cranks up the
heater.
I'm in west Texas with very hard water - it is highly recommended that you
have
a water softner in place in hard water conditions.

Give Noritz a pre-sales call, they were very helpful when I spoke to them.
I considered zoning two units, but the sales guy conviced me the N-069M
would be
sufficient, but suggested that if you ever needed to, you could simply add a
second unit. They are designed to work in tandem with a connector cable.

....Bob