Navien NR-210A

This gas tankless water heater avoids the problem of small, sudden spurts of cold water by building in a buffer tank and a recirculating pump. By eliminating any wait to get hot water when you turn on a faucet, this avoids wasting water and saves energy. Like all the Navien NR tankless water heaters, this middle-sized model uses condensing technology to provide an outstanding thermal efficiency of 0.98, meaning almost no gas fuel is wasted. Needless to say, this water heater earns Energy Star certification, so when it replaces the water heater in an existing primary residence, the installed price is eligible for the 30 percent federal tax credit as well as the state "cash for appliances" rebate and other incentives. If you're replacing a storage-tank water heater for a more energy-efficient model that delivers more hot water for peak usage, you can minimize installation costs by going with a storage-tank condensing water heater (also Energy Star certified), the A. O. Smith GDHE-50 Vertex 100 (*Est. $1,940).

We didn't find the Navien brand covered in reviews or in brand surveys of contractors and builders. We did find enthusiastic articles about the Navien NR series by plumbing contractors. The well-illustrated Alpine Heat Blog comments on actual installations of these water heaters, showing how they look and perform in real-life situations. The review at 411plumb.com summarizes the features and advantages well, but doesn't document any testing. At the Journal of Light Construction, Jim Lunt argues that storage-tank condensing water heaters are a better bet for replacing other storage-tank models.