The 10 Best Tankless Water Heaters
Updated by · How we research
Gas, electric and point-of-use heaters compared on flow, wiring and venting needs. The Rinnai RX199iN leads for busy homes on natural gas. When users buy our independently chosen editorial selections, we may earn commissions to help fund the Wiki.
A tankless heater's flow rating assumes fairly warm incoming water, so a unit that runs two showers in Florida may manage only one in Minnesota. Gas models push the most water but need venting and a licensed installer. Electric ones skip the vent and cost less up front, yet many homes need a bigger electrical panel to run them.
Editor's Notes
November 1, 2026, by Ezvid Wiki Admin:
The Rinnai RX199iN is the new pick for most gas homes. It condenses its exhaust, so nearly all of its gas becomes hot water, and it can feed several showers at once. Rheem's RTG 7.0 Indoor is the lower-cost gas choice, and the Stiebel Eltron Tempra 24 Trend leads for homes that run on electricity.
Only the Rheem RTEX-13 survives unchanged from the old list. The outdoor Rheem RTG-84 line returns as the current Rheem RTG 8.4 Outdoor. The Takagi T-H3, the DLTSLI Instant Electric and several others dropped out because they have left the market, and the Rinnai Ultra Series has been replaced by newer models.
We sized each pick against the flow and groundwater math in three home-improvement guides, read each maker's breaker, gas and venting requirements, and checked every brand with the CPSC. Camplux recalled some propane camp heaters in 2024; its electric model here isn't part of that recall.
January 28, 2021:
It was a relatively uneventful round of updates, as most of our previous picks remained great choices for the category. We did notice that the Rheem RTG-84 and Camplux 5L Portable appeared to be suffering from some availability issues, but decided to retain the former option – as it seemed to be suffering from a temporary shortage – while we removed the latter — as it was less clear if or when this option would be stocked again.
We also added the Dltsli Instant Electric to our list — a compact option that makes a great choice for tiny homes or small vacation cabins, although it will likely have a hard time keeping up with multi-person residences. We liked that this option came with a convenient remote control, which might seem like a useless luxury, but we thought it was an interesting asset, as it allows you the freedom of installing the unit just about anywhere, even if it isn’t conveniently accessible.
January 16, 2020:
During this round of updates, we removed the Takagi T-KJR2, due to availability issues, and replaced the discontinued Stiebel Eltron Tempra with the company’s new, deluxe offering the Stiebel Eltron Tempra Plus. We also introduced the Ecotouch ECO90, a 40-amp offering that caught our eye with its smart design and list of features.
A few things to keep in mind while you’re shopping:
Capacity: While traditional hot water tanks are limited by the volume of water they can hold (normally 50 or 70 gallons in a residential context), tankless water heaters are limited by the rate of flow they can heat instantaneously (normally expressed in gallons per minute). So, whereas hot water tanks are limiting in the number of sequential showers they can deliver, tankless water heaters are limiting in the number of simultaneous showers they can deliver.
You want to make sure you select a unit with a maximum flow rating that can accommodate all the potential simultaneous hot water needs of you and your family. Note that in the case of two identical families living in different climates, the family living in the colder climate will require a higher maximum flow rating, to offset the natural temperature of the water. The Ecotouch ECO90, for example, is a smaller unit that can heat up to 1.5 gallons of water per minute (from 67 Fahrenheit to 106 Fahrenheit). Based on this, the company notes that it might have trouble heating water for showers in colder climates (showers usually draw around 2.5 gallons per minute). So, users who live in colder climates, or houses where simultaneous showering is likely to occur, should definitely look into a larger unit that can meet their needs. Alternatively, a family could also consider setting up several units throughout the house, at each point of use – one for the laundry room, kitchen and each bathroom.
Energy Source: Tankless water heaters are typically powered by either electricity, natural gas or liquid propane. Although it can sometimes present an inflated up-front cost, natural-gas equipment is typically a more-efficient means of generating heat, and can save you money in the long run, when compared to electric options. Nautural-gas models are also great for users who already have natural-gas service in their home, but limited electrical service. Liquid-propane models, though much less common than their alternatives, can present an option for users trying to outfit a home with limited electrical service and no access to natural gas, making them a great choice for recreational vehicles and remote cabins.
Installation: In virtually any circumstance, installing one of these units for the first time will involve new rough-in electrical work and sometimes, as in the case of natural-gas models, require that new gas lines be put in place. Natural-gas options also have the disadvantage of requiring venting for every heater installed, which presents an additional cost and makes it necessary to compromise your home’s vapor barrier. Because of these extra factors, users leaning toward a natural-gas model, over an electric option, will likely want to consider a single unit that can service their entire home, whereas the prospect of multiple, smaller electric units might make practical sense in some situations
Regardless of what type of tankless water heating system you decide to install, your installation should always be completed by a reputable, licensed gasfitter and/or electrician.
Special Honors
Navien Navien, a Korean maker, builds condensing gas tankless heaters and combination boilers that several plumbing companies rank at the top of the category. They're sold mostly through installers rather than online, so ask a local plumber for a quote if you want one. navieninc.com
Size It By Flow And Incoming Water Temperature
Gas makers usually rate flow at a 35-degree rise, which fits the South.
A tankless heater has no stored supply, so its limit is how many gallons a minute (GPM) it can heat at once. Add up what runs at the same time. A shower uses about 2 to 2.5 GPM, a washing machine about 1.5, a dishwasher about 1 and a bathroom sink about 0.5 (This Old House, Popular Science). Popular Science puts a family of four at about 6 to 8 GPM.
The second number is temperature rise: the gap between your cold inlet water and the hot setting. Gas makers usually rate flow at a 35-degree rise, which fits the South. In a northern winter the inlet water can be 40 degrees or colder, and the same heater delivers far less. Bob Vila's electric guide notes that rated flow assumes warm inlet water and drops in cold regions (Bob Vila).
So size for your coldest month. Bob Vila suggests about 5 GPM for one or two bathrooms and about 10 GPM for three or four (Bob Vila). If one heater can't cover the house, a small point-of-use unit at a far sink can take some load off the main one.
Gas, Electric Or Point Of Use
Condensing gas heaters capture heat from their own exhaust. They run at about 90 percent efficiency or better, vent through plastic pipe and need a drain for the acidic condensate. Non-condensing models run at about 80 percent, and their exhaust can reach 300 degrees, so they need a stainless steel vent (Bob Vila). Outdoor gas models skip the vent entirely but need freeze protection where winters are hard.
Whole-house electric heaters are nearly 100 percent efficient at the unit and need no vent, but they draw a lot of current. A rough rule is about 4 amps per kilowatt, so a 24 kW model draws close to 100 amps and needs two or three large double-pole breakers (Bob Vila). Many older homes need a 150- or 200-amp service, or a panel upgrade, before an electric unit makes sense. Electric models cost less to buy but usually more to run than gas (Popular Science).
Point-of-use heaters are small electric units for one sink, a dishwasher or a garage bathroom. They cut the wait for hot water at a far tap, but they can't serve a whole house.
Installation, Safety And Upkeep
Gas models need a licensed plumber. Many need a larger gas line than an old tank used, a vent run that meets code, a permit and an inspection. Some makers tie their warranty to professional installation (This Old House). Keep a working carbon monoxide detector near any gas appliance. For electric models, an electrician should confirm that the panel has room for the breakers and that the wire is the right size.
Set the temperature to 120 degrees or lower to prevent scalds, especially in homes with children or older adults.
Scale is the main enemy, especially with hard water. Flush gas units, condensing models in particular, about once a year with a pump and white vinegar (Bob Vila), and clean the inlet screen filter on electric units (Bob Vila). With that care, a tankless heater can last about 20 years, against 8 to 12 for a typical tank (Popular Science). Register the unit soon after installation: Rinnai, for one, extends its labor warranty only for registered heaters.
How we researched this
We compared 22 tankless water heaters, gas and electric, read the makers' flow, breaker, gas and venting specs for the 10 finalists, weighed the sizing advice and picks in Bob Vila, This Old House and Popular Science guides, analyzed owner feedback patterns, and checked every brand against Consumer Product Safety Commission recall records. We found no independent lab measurements of these heaters.
Frequently asked questions
Is gas or electric better for a tankless water heater?
Gas delivers more hot water at once and usually costs less to run, but it needs venting, a suitable gas line and a licensed installer. Electric costs less to buy and needs no vent, but large models need a lot of electrical capacity.
What size tankless water heater does a family of four need?
About 6 to 8 gallons a minute, according to Popular Science. That usually means a gas unit, or a 24 to 36 kW electric unit in a warm region. Size for your coldest month.
How long do tankless water heaters last?
Up to about 20 years with yearly flushing, against 8 to 12 years for a typical tank.
Does a tankless water heater need a vent?
Indoor gas models do. Outdoor gas models and electric models don't.
Can I install a tankless water heater myself?
Gas models should be installed by a licensed plumber, usually with a permit, and some warranties require it. Electric models need an electrician to check the panel, breakers and wiring.
Can I buy these in Canada?
These are U.S. models. In Canada, look for a CSA-certified version sold by a Canadian retailer, so the warranty and local codes are covered.
