I had a Noritz N-69M-OD installed a couple of months ago.
I am remodeling the utility/mud room, and getting the old heater out of there gives me room for front loader washer and dryer on the outside wall.
This is the only part of the remodel I wanted to hire out. Utility company put in the new gas meter for no charge (2lb service). I had a local mechanical contractor come out and install the heater, new gas line for dryer for 2000 including the heater. Federal tax credit is $300, local utility gave me a check for 350 for putting in an efficient gas heater. So for 1500-1600, I got more space in the house, and a more efficient unit.
The past 2 months, my gas bill has been about 40% of what it normally would be (most of the summer we use the grill, so hot water is the only real gas use). This only = about 15.00 month in savings, but:
1500-1600.00
1) More space in a house where space is at a premium. (This was really the biggest plus for me, any utility savings is just gravy)
2) Lower gas bill.
3) Hot water lasts forever.
4) Remote is cool.
5) Will enable me to solve the problem of a dryer on an inside wall with a 30' vent (2 sharp angles). This should also cut down utilities.
I had a 2 plumbers give estimates on relocating a tank heater about 10' into the garage (they did not do tankless, for some reason). They both wanted to put in a new vent (I would be responsible for flashing, etc. at roof). For this, and re-routing plumbing and gas, their bids were about the same (1450 and 1600).
For me this decision was a no-brainer, and I don't regret it at all.
**Outside unit requires no venting, which saves on the materials/install.
**There is a yearly maint. to do, but really amounts to the equivalent of cleaning out a really big coffee machine.
The one thing I do think about is waiting on repair parts when it breaks down. I'm in north central Florida though, so 6 months out of the year, I can probably rough it if I need to.