Stay far away from Rheem. We bought 2 Rheem gas tankless exterior water heaters in Feb.08 for our home, that had previously been 2 rental units with separate plumbing systems. From the start, we had problems. The units were serviced at least 4-5 times during their first year. Once the one-year service warranty ended, the problems continued unabated. We've had 5 service calls since last February. The repairman has replaced the computer brain twice, re-located the igniter, replaced an internal gasket, etc., etc., etc. Both units have been problematic, but one has been serviced more than the other simply because we are in the midst of a very long kitchen renovation and don't use the second one very much. Rheem eventually offered to replace the unit, tho not cover installation. We have spent so much repairing the units that I'm hesitant to spend another $200 installing a new one. Would we then have to continue paying to have the igniter moved and the computer brain replaced? We will try to get more life from our units before replacing them with Noritz. Buyer beware- this has been a terrible disappointment.

So far I've only heard good things about Navien from installers - highly recommended. SR

I'm a bit late to respond but I'll give you my input on how our Noritz M-084M is working in Sammamish (Seattle area), which is to say, great! The 8.4 GPM is for a 45 deg temp rise, the lower 5 or 6 GPM is for a higher temp rise needed in Winter. You can find the charts on the Noritz website. I have our unit set to 120 deg and it works well at that setting. Our kitchen is the farthest from the unit, which I installed in the garage attic, and with the temp set at 120 I run the faucet on full hot when doing hand washing of dishes and this is just fine. I find the unit actually works better with COLDER incoming water temp. In the summer the temperature at the kitchen seems to be lower for some reason. The highest load we put on the unit is running two showers at once, which we do on the weekend. It has absolutely no problem keeping up and the water temp stays nice and constant. Our unit is rated at 0.75 GPM to activate, and there is no problem at all to get it running with a bath faucet. Newer units are 0.50 or below. And once it's running it seems like you can turn it down below the 0.75 GPM rate and still get hot water. Go too low though and it will shut off and you'll get the dreaded slug of cold water. This happens very infrequently and has not been any problem. If you haven't purchased a unit and would like to see our installation, drop me an email. I have some pictures or you could come out and take a look in person. Tom

There is a LOT of disinformation on these forums about on-demand tankless units, ESPECIALLY the electric units. First, energy cost savings is NOT a reason in itself to make the switch. No reason alone is sufficient. It is the total package, in light of your particular lifestyle, that will dictate the pro-con outcome of the decision making process. First, tankless units save space -- a lot of it, especially electric units that do not need to be vented. In Texas we have no basements, so that can be an important issue. Second, an electric unit is unlikely to blow up, unlike anything using natural gas. Third, there is an endless supply of hot water, which in a successive-morning-shower household like mine, is a really important issue. And finally, yes there is some documented comp fuel savings (electric tankless over electric tanks, or gas over gas), that is really offset by the added initial cost of the unit plus upgraded electrical service or gas supply line sizing. Moreover, there ARE full-house electric units out there that provide plenty of water, unless you plan on taking two showers simultaneously while also doing your laundry and running the dishwasher! And if that's your bag, you can run 2 or more electicals together. Or get a really big gas unit. Bottom line, nearly every nay-sayer of tankless units ignore the pros and focus on a single con - cost, cost, cost. Well, we all don't drive a Ford Focus for a reason. Some of us enjoy our Buicks, Porsches or Camrys even though another car would get us from point A to point B cheaper while using less fuel etc etc etc. Full disclosure: I have a Steibel Eltron Tempra 36 whole-house electric unit. Love it. My electric bill went up nary at all.