I've been extensively researching gas tankless heaters because I'm about to buy one as part of a major remodel of my home. I haven't found very good cost information aimed at the involved homeowner, so I thought I'd start a thread. There are plenty of threads on pro installer sites on costs that are useful and informative to read, but they are aimed more at how to profit from the homeowner. I have nothing against plumbers, but I want mine to make no more than a fair and reasonable profit doing this job. Anything I can do to control costs, including sourcing parts myself, I will do. I am buying all fixtures and providing them to the installer. First - my project description. When I say major remodel, I mean we are tearing our 1940s house down to the studs, demoing all interior walls, and building up a floor. We are replacing all utilities (water, gas, electric) completely and can site them where we want. So practically speaking, this is new construction, though it is permitted as a remodel (which qualifies me for the federal tax credit). There isn't any incremental plumbing cost to going tankless, since all of the gas and water plumbing is already covered by my construction loan. The plumbing is all PEX. We did specify a hot water return system for recirculation, and that added about $500 to the plumbing bid. Second - my tankless system. A recirculating system is a must, I'm convinced. Research it and draw your own conclusions, but I'm not even considering a static on-demand system. We will have only 2 full baths, but one has both a multi-head shower and a large soaker tub. Our groundwater temp in Seattle is 50degF. I want a fairly high capacity system. I'm looking at 8.5+ gpm systems for a 45 to 50 deg rise. It will be mounted on an external wall in the basement level garage, and direct vent horizontally. Very simple installation. The two bathrooms are directly above the heater, with the master two floors up, and the guest bath between. So, the question is what system to buy? My plumber's recommendation, echoed by many professional threads I have reviewed is a Rinnai TWH (R94LSi or comparable), feeding into a 4 gal electric buffer tank that feeds the recirc system. I can direct purchase that unit for about $1100 shipped. The additional parts I need, including concentric vent, buffer tank, and circ pump with timer will set me back another $500 at least. Intellectually, I don't like the idea of using an electric resistance heater for the recirc, but it is the cheapest option, and the only one Rinnai will approve for warranty purposes. I know it will work, and won't cost that much if I limit the recirc to heavy use times. This unit has an energy factor of 0.82. Rinnai's condensing TWH (RC98HPi) gets you up to 0.93 EF, and can be owned for about $1400. Option two is to go with a unit that has an integral buffer tank and pump, such as the Navien NR240A. I can get this unit delivered for $1700, with nothing else significant to buy. It vents in and out through ordinary 3" PVC, and two holes is not a problem for my installation. The 240A is a condensing unit with a 0.98 EF, so is quite a bit cheaper than the equivalent Rinnai and easier and neater to install. It also has a standard remote control that allows you to program temp and recirc timing from a convenient spot in the house. Both of the above systems are eligible for rebates from my local utility ($150 for 0.82+ EF or $200 for 0.90+ EF), as well as the federal tax credit (30% of installed price). That brings the non-condenser Rinnai system down to $970. The condenser Rinnai system is $1130. The Navien system would be $990, which looks like the best deal. Installation of the Navien isn't any different than a tank heater, other than the recirc return. I might have to pay a little extra labor to plumb the external tank and pump on the Rinnai, depending on my plumber's mood. The real question on the Navien is reliability. The installer forums all rave about the Rinnai reliability. There are more in service than anything else, and people are used to them and know how to deal with them. They apparently rarely break. The early generation of Navien TWHs (CR-xxx, circa 2008-2009) had a lot of problems, and there are a lot of Navien haters out there because of it. You can learn a lot from reading the pro blogs and forums. I highly recommend it. Plumbers are not a forgiving bunch though, and one bad product will put them off a brand til the day they die. From what I can tell, the newer 2010 NR-xxx heaters work as advertised. One of the moderators here has one in his home and loves it. I haven't found the rants among the installers that were there a year or two ago for the old model (though some have neither forgiven nor forgotten all the angry customers and service calls). Clearly, the weight of expert opinion comes down more in favor of Rinnai though. To some degree, this is due to inexperience and hearsay about Navien. So I hope this narrative is useful to other homeowners, and I hope others will post their opinions and recommendations, based on real experience. If I am missing something, I really hope somebody will point that out. I am not a heater expert, just a consumer trying to get educated.