It is made by Rinnai. I sell them at my place of business and I am simply amazed by the performance of this machine.
For those who don't know about these, a little background.
Tankless water heaters are just what their name implies - water heaters without tanks. They heat water as it passes through the unit. I know it is hard to believe but it works like a champ. To understand how, you first have to realize that standard tank water heaters have a 40k btu plate burner on the bottom. This unit modulates from 18k up to 180k btu depending on demand.
There is a rack of burners inside the unit. The computer does many calculations every second measuring incoming water temp, outgoing water temp and flow rate and comes up with how many burners to have on. You can see right off the bat how this saves energy - if you have one sink on, you will more than likely get the minimum burner set. If you have on two showers, the dishwasher and a sink, you will get more burners on. When there is no demand, the unit sits idle. Contrast this to your traditional tank heater. When you go on vacation or are at work, if you don't set your water heater thermostat down (who does this?) you are constantly heating this large container of water to a certain temperature. Then when your water heater ages, and limes up your recovery rate goes way down. More lost energy.
There is no guarantee that a tankless heater won't lime up but the odds are slim. There really isn't much water (any?) stored inside the unit at a high enough temperature for the solids to come out of solution and cake the heater up. If this does happen though, there is a lime sensor inside and it will flash the appropriate error code on the keypad. The simple solution is to valve the unit off with the valves you see below the heater, and run vinegar through it with a pump. Problem solved.
The venting you see on the top is what is called a concentric vent. This means that it is a circle within a circle. Like this:It takes combustion air from the outer ring and sends to the outside of your house the combustion products through the inside portion. This is great because you aren't using your already heated or air conditioned air inside your house and sending it outside - you are bringing in outside air for combustion.
To boot this thing is very quiet.
As a wholesaler of water heaters, these units are becoming more affordable every day. To the dealer, they are only about $200 more expensive than a single pipe power vented traditional water heater. And the federal government will give the homeowner a $300 tax credit (not a writeoff, a CREDIT) for installing one of these as they are so efficient for the reasons posted above. If it is time for you to replace your water I highly recommend this particular brand as it has many more features than some other brands you will find in home centers.
One problem I had with mine I should share. When it was installed it was discovered that the water pressure entering my house was very high (almost 90 psi) from the city. So when this heater was installed we got a severe case of water hammer. Why? Before, when we turned our faucets off the water had that large tank to slosh back into. With that removed, all of the energy had to be dissipated by the pipes - so they shook and banged. This problem was fixed by installing a water pressure regulator and an expansion tank. You can see the tank in the upper left of the photo.
By the way, please ignore all the cords in the photo, I am re-doing my wireless network setup and have not cleaned up the installation yet. They don't have anything to do with the heater. Also ignore the large pvc pipe you see coming across and down - that is a radon removal unit and also had nothing to do with the heater.