The Best Tankless Water Heaters
A tankless water heater looks to be nothing more than a simple gray box that hangs on the wall. Yet inside that box is some pretty remarkable engineering, because when you open a hot-water faucet, it delivers luxurious amounts of hot water while still being relatively energy efficient.
Check out quick info below on five tankless water heaters we recommend. Scroll deeper for the explanation on how these appliances work, helpful buying advice, and full reviews.
How They Work
When you open a faucet in your home, cold water enters the appliance and triggers a flow sensor. For electrical appliances, this activates the circuit to energize a heating element, which warms the water directly. For gas appliances, it opens the gas valve and energizes the igniter. A burner then fires inside a heat exchanger; water is heated when it makes contact with the exchanger’s hot metal surface. The appliance’s flow sensor and circuitry adjust the output to meet demand. The colder the incoming water, the harder the appliance must work. Other sensors and circuitry guard the appliance against overheating. After all that, the result is nice warm water, and as much of it as you’d like.
When you’re done using hot water, the appliance senses the lack of water flow and turns off the heat, saving energy. The energy savings can be substantial, perhaps as much as 24 to 34 percent annually (according to studies by the US Department of Energy) compared to a convential tank type appliance. This doesn’t guarantee that the appliance’s energy savings will achieve a payback, however. Generally speaking, the appliances are more expensive to buy, install, and service than a typical tank type water heater. Retrofitting them into an older, less energy efficient house that was originally designed for a tank type water heater can sometimes be complex, accounting in part why installing one can be expensive to the point that its econonic attractiveness is reduced. But tankless heaters do ensure two things: The luxury of having all the hot water you want (and quickly), and space savings derived from their small size and location on a wall, not the floor. And we'll add one cautionary note here. If you take advantage of all that hot-water capability for long steamy showers, you'll need to vent your bathroom accordingly (of course, increased bath fan use or a larger bath fan will reduce your energy savings). A poorly vented bathroom (and most are) is a major source of mold and damage related to the effects of moisture vapor condensing on and in wall surfaces, grout, on windows, and ceilings.
Picking a Tankless Water Heater
Some mechanically gifted people install tankless water heaters themselves, but most are installed by a licensed professional, usually a plumber. (Some manufacturers void the equipment’s warranty if it hasn’t been installed by a licensed professional.)
Before you buy an appliance, check with the technician who will install it and verify whether you’ve correctly sized it. To do that, consider the largest demand that the appliance will regularly have to meet (i.e. multiple showers at once). Next, consider whether the appliance can heat the incoming water enough (called temperature rise) to meet that demand. Manufacturers provide sizing and temperature rise information to help you make your selection.
And as to fuel-burning versus electric, if you’re replacing a tank water heater, you’ll probably use the same energy source. And as to its size, use the manufacturer-supplied dimensions to be sure that it will fit where you intend to install it. In warm climates, tankless water heaters can be installed on the outside house wall, but be aware that building codes determine their location relative to eaves and whether they are near a window or door.
There are also very small tankless and mini-tank models that can be installed right where they’re needed, such as under the counter at a sink that’s far from the main water heater.
And many tankless products can be controlled remotely via an app. Think about that if you are having a tankless installed in a vacation home. You can take the appliance out of the “vacation” setting ahead of time and fire it up for a hot shower when you arrive or shut it down remotely.
How We Selected
We chose this range of water heaters to give you a cross section of these appliances in terms of physical size, price, capacity, energy source, and mechanical characteristics—such as mineral scale sensors or the ability to be linked with other tankless heaters. To do that, we relied on our expertise from past coverage and testing of home appliances to research which heaters could serve your needs best. We considered those fired by natural gas or propane and ones that operate on electricity.
Rinnai V65IN
Fuel: Propane | Location: Indoor
Ideal for small or mobile homes, the V65IN is a mid-price appliance that the manufacturer rates as being capable of serving up to five different fixtures at the same time. During warm weather, when the supply water is at its optimal temperature, the appliance may be able to provide up to 6.5 gallons of heated water per minute. And a handy feature that detects scale buildup will shut the appliance down rather than risk overheating damage caused by a buildup of mineral deposits.
Rheem RTG-84DVP
Fuel: Propane | Location: Indoor
A high-efficiency appliance designed for rural and suburban homes running on propane, this Rheem extracts every last ounce of heat energy using a second heat exchanger that pulls heat out of the exhaust gas (a condensing appliance, in other words). Under optimal water temperature conditions, it can provide up to 8.4 gallons of heated water a minute. That’s a lot of hot water, and it would be unlikely that you need more.
Bosch ES4 Tronic 3000
Power: 120 volts | Location: Indoor
You know that bathroom sink that’s farthest from the heater, that never seems to get hot water? Well, this is the answer. Not a typical tankless water heater, the Bosch ES4 tucks under a counter or inside a cabinet and plugs into a standard wall outlet to provide all the hot water that sink will need. It can also be plumbed in line to supplement a separate tankless water heater, taking some of the load off of it, an especially useful feature to help supply high-demand fixtures far from the tankless heater.
AO Smith ATO-310-P
Fuel: Propane | Location: Outdoor
You’ve got this cabin on the lake, and you’re tired of not being able to take a decent shower after a day of water skiing or mountain biking. This 38-pound tankless heater will do the job, especially when you consider its outsized performance of delivering nearly nine gallons of heated water a minute. Don’t have a cabin? The appliance works in the suburbs, too. Either way, install it outside on an unobtrusive back or sidewall and no one will be the wiser. It can supply two fixtures at the same time, and a temperature remote control can be installed indoors (in a closet, if you prefer, to keep your kids from tinkering with it) to adjust the water temperature. That way, you don’t have to go outside to adjust the appliance.
Takagi T-H3-DV-N
Fuel: Natural gas | Location: Indoor
Among the thriftiest and most energy-efficient tankless water heaters that you can find is this condensing high-efficiency model from Takagi. It’s also physically small and relatively light, weighing 58 pounds. And if for some reason it turns out that you need more capacity than this appliance can provide (unlikely given its efficiency and capacity to supply up to 10 gallons of heated water per minute), it comes from the factory engineered to be linked up to three other heaters without complex accessories or parts kits.
Rheem RTEX-18
Power: 240 volt | Location: Indoor
A 240-volt tankless water heater is the solution for a lot of homeowners who don’t have gas service at their house and, for whatever reason, propane is impractical. This Rheem appliance weighs only 8.5 pounds and is roughly the size of two laptops stacked on top of each other, so it can be installed on a small wall area and wired in an unobtrusive way with size eight AWG wire (and two 40-amp circuit breakers). Its self-modulation feature detects water flow and adjusts its power output to meet demand, saving electricity.
Rinnai V65eN
Fuel: Natural gas | Location: Outdoor
Space is tight in your house and you want to fully capitalize on removing the old water heater that’s now stashed in a utility closet. So you have a plumber install the V65eN on an outside wall, freeing up the closet space, cutting your gas bill, and getting more hot water for your utility dollar. Not bad for a day’s work. Other aspects of this low-cost appliance make it appealing, such as its 6.6 gallon-delivery rating. Rinnai rates it as suitable for homes with a single or 1.5 baths.
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