Tankless water heaters have always been full of promise. By heating water only when you need it, the suitcase-sized units could potentially save homeowners lots of energy and a bit of storage space, plus the endless hot water supply meant no more cold showers. But our first tests of tankless water heaters back in 2008 found that they didn't always deliver, especially when they were replacing an existing conventional water heater. Between their steep upfront costs, complicated installations, and inconsistent water temperatures, thankless water heaters was more like it.
Manufacturers haven't given up on the technology, however. And their commitment might just be starting to pay off. Many of the tankless water heaters on display at the recent Design & Construction Week trade show claim to address those early growing pains. Here are the most common past problems, and how this latest generation of tankless water heaters is addressing them. We'll find out if the promises are for real when we get the units into our labs for testing.
Solution: Improved designs promise to make it easier to switch from a conventional tanked unit to a tankless one. The manufacturer Noritz, for example, is positioning the input and output waterlines at the top of its units, instead of at the bottom, which used to be the norm. That mirrors the location of the lines on tanked units, simplifying the retrofit. Noritz also has a flexible exhaust pipe with a proprietary adaptor that allows it to be connected to existing ductwork more easily than the standard PVC piping.
Several manufacturers are also saying that their new tankless water heaters will work with existing 1/2-inch gas lines. That wasn't common when we last tested the units, and it should make retrofit installations easier and less expensive
Solution: Manufacturers have also tackled this issue. Rinnai, for example, has added a recirculation pump to its units to ensure that water comes out hot from the start and stays that way for as long as it's running. Korean manufacturer Navien goes one step further by including a buffer tank on certain models that stores a ready supply of hot water. That eliminates the cold-water sandwich and ensures consistent temperatures.
Solution: During our last long-term testing, scale buildup was a big concern, since it could decrease efficiency, restrict water flow, and eventually damage tankless models. In homes with hard water, installing a water softener was recommended, which added to the upfront costs. Rinnai has addressed this issue by developing isolation valves that make routine maintenance and descaling the unit easier.
Even with these innovations, tankless water heaters aren't for everyone. For example, if your current water heater is electric and you don't have natural gas or propane capability, a tankless model might not make sense because you'd almost need to double the capacity of your electrical system to power the electric tankless unit. Also, if you live in an area with extremely cold incoming ground water, you'd need a very large capacity tankless unit, and maybe even multiple units, to get the water hot enough—and that might not be practical.
With these caveats in mind, today's tankless water heaters could be worth a look.
—Daniel DiClerico (@dandiclerico on Twitter)