The 6 Best Tankless Water Heaters of 2026 (The GPM Number Is Not Your GPM)

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Our quick picks

Ranked by what each one is best at, not by a score we made up. Ratings are what the product showed on Amazon when we last checked — how we rank.

Everything below is the why: the specifications that settle the choice, and where each pick falls down.

The gallons-per-minute figure on a tankless water heater is only true at one specific temperature rise, and if you live anywhere cold it is not the number that applies to you.

Here is what that means. A tankless heater does not store hot water; it heats water as it flows past a burner or an element, and how much it can heat depends on how far it has to raise the temperature. Manufacturers usually quote their headline flow rate at a modest rise — often around 35 degrees Fahrenheit — because that produces the biggest number. But in January in a northern state, incoming water might be 40 F and you want 120 F at the tap. That is an 80-degree rise, and the same unit that delivers 8.4 gallons a minute at a 35-degree rise might manage half that.

Get this wrong and the symptom is precisely the thing you bought a tankless heater to avoid: two showers running at once and the water going lukewarm. It is the single most common regret in this category, and it is entirely avoidable with five minutes of arithmetic, which this guide walks through.

Below are six units covering gas and electric, whole-house and single-fixture. Before any of them, though, there is a section on installation and safety, because this is a category where getting it wrong involves gas, venting and combustion products rather than a disappointing purchase. If you are working on your home’s plumbing generally, our guide to the best water filters covers the other half of what comes out of the tap.

Quick picks

• Best overall: Rheem RTG 8.4 GPM natural gas — the highest-rated unit here by a clear margin, sized for an actually large household.
• Best compact gas unit: Rinnai V53DeN — a smaller, efficient gas heater for a modest home or a warm climate, from the brand that largely created this market.
• Best gas unit with app control: Westinghouse 7.9 GPM — WiFi and voice control plus tight temperature stability, which matters more than it sounds.
• Best whole-house electric: Stiebel Eltron Tempra 29 Plus — no venting, no combustion, and the most capable electric option here.
• Best value electric: ThermoMate 14kW — a sensible whole-house electric unit for a warm climate or a small household.
• Best for a single sink: CAMPLUX 6kW point-of-use — a small 240V unit for a remote bathroom, a workshop or a garage sink.

Read this first: installation, gas, and safety

This section comes before the product recommendations because a tankless water heater is not a plug-in appliance, and the consequences of a bad installation include carbon monoxide, gas leaks, electrical fires and scalding. Nothing here replaces your local building code, the manufacturer’s manual, or a licensed professional.

For almost everyone, this is not a DIY job

We say that plainly because the listings do not. A gas tankless heater typically requires all of the following, and every one of them is a place where amateur work causes real harm:

• Gas supply sizing. Tankless units fire at a far higher rate than a storage tank — commonly 150,000 to 200,000 BTU per hour against a tank’s 40,000. Existing half-inch gas pipe is frequently too small, and undersized gas supply causes the unit to run badly or not at all. Upsizing the line is a licensed job.
• Dedicated venting. You cannot reuse the old water heater’s chimney or B-vent. Non-condensing units need stainless steel category III venting; condensing units use plastic. Using the wrong material or a bad joint can put combustion products, including carbon monoxide, into your house.
• Combustion air. The burner needs air. In a sealed utility closet that means either a direct-vent (sealed combustion) unit or dedicated air supply.
• Condensate drainage. Condensing units produce acidic condensate that needs a drain and usually a neutraliser cartridge.
• Permits and inspection. Most jurisdictions require both for gas appliance work, and an uninspected installation can affect your insurance and your house sale.

Whole-house electric units avoid the combustion issues entirely and bring a different problem: electrical capacity. A large electric tankless heater can draw well over 100 amps at 240 volts, which usually means multiple double-pole breakers, heavy-gauge wire runs, and often a service panel with genuine spare capacity. Many homes need a service upgrade, which is expensive. Have an electrician check your panel and your service size before you order anything.

And regardless of fuel: if you have any gas appliance in your home, you should have working carbon monoxide alarms on every level, tested regularly. That is true whether or not you buy anything on this page.

Set the temperature to avoid scalding

Tankless heaters let you choose an outlet temperature, and the temptation is to set it high. Resist it. Water at 120 F is hot enough for showers and washing up, and the risk of a serious scald rises steeply above that — notably fast for young children, older adults, and anyone with reduced skin sensation or slower reactions.

One genuine advantage over a storage tank is relevant here. Tank heaters are often set to 140 F because standing water in a tank can support bacterial growth, and then a mixing valve blends it back down. A tankless heater stores essentially no water, so that reason to run hot largely does not apply, and you can keep the outlet temperature at a safer setting without the same trade-off. If anyone in your household is at particular risk, thermostatic mixing valves or anti-scald fixtures at the point of use are worth discussing with your plumber. Any specific health concern about water temperature is a question for a professional rather than a product guide.

How to size one properly

This is the part that decides whether you are happy, and it takes five minutes.

Step 1: add up the flow you want to run at once

Typical flow rates for modern fixtures, in gallons per minute:

• Shower head: 1.5 to 2.5
• Bathroom faucet: 0.5 to 1.5
• Kitchen faucet: 1.5 to 2.2
• Dishwasher: 1 to 2.5
• Washing machine: 1.5 to 3

Decide your realistic worst case. Two showers at once is roughly 4 GPM. A shower plus a kitchen tap is about 3.5. One shower alone is 2. Be honest rather than aspirational — sizing for a scenario that happens twice a year is how people end up paying for capacity they never use.

Step 2: work out your temperature rise

Subtract your incoming cold water temperature from your target. Groundwater temperature varies by region and season; in the southern US it might be 65 to 75 F in summer, while in the northern states it can drop to the high thirties or low forties in late winter. Use your coldest realistic figure, because that is when the heater will disappoint you.

• Warm climate: 70 F incoming, 120 F target = 50-degree rise.
• Temperate: 55 F incoming, 120 F target = 65-degree rise.
• Cold climate in winter: 40 F incoming, 120 F target = 80-degree rise.

Step 3: read the manufacturer’s flow chart, not the headline

Every reputable manufacturer publishes a table or graph of flow rate against temperature rise. Find the row for your rise and read off the flow. That figure, not the number in the product title, is what the unit will deliver in your house. If it is below the total you calculated in step one, you need a larger unit, two units, or to accept that you cannot run two showers at once in February.

This single step is what separates a happy tankless owner from an unhappy one. It is also why gas units dominate in cold climates: getting an 80-degree rise at 5 gallons a minute takes a great deal of energy, and delivering that electrically requires an electrical service most homes do not have.

How this list was made

We built this list from current Amazon listings, manufacturer specifications and the recurring patterns in verified buyer feedback. We have not installed and lived with these units, and we are not going to imply we ran efficiency measurements. What we did was check that the specifications are coherent for the use case claimed, that the flow ratings are stated honestly with a temperature rise attached where available, and that the brand has a service and parts network behind a product that will be plumbed into a wall for a decade or more.

We weighted heavily toward brands with established service networks, because a tankless heater is not a product you replace casually — when it faults, you need someone who can get parts. We weighted heavily against recurring reports of error codes with no resolution, of poor technical support, and of units that struggle at low flow.

Every pick holds a customer rating of 4.3 stars or better. Several very well-known models sit at 4.0 to 4.2, including a flagship from one of the most respected names in the category; where that is relevant we say so in the entry. Reviews of plumbed appliances are noisier than most, because a badly installed good unit generates the same one-star review as a faulty one — so we read the complaints for what they described rather than counting them.

What else to know before you buy

Gas or electric?

This is usually decided for you by what you already have.

• Gas delivers far more heating power for a given cost, which is why whole-house tankless in cold climates is overwhelmingly gas. The costs are venting, gas line sizing, combustion air and permits — a more involved and more expensive installation.
• Electric needs no venting, no gas line and no combustion air, so the unit can go almost anywhere including a closet or under a sink. It runs quietly and has fewer things to go wrong. The constraint is electrical service: whole-house electric tankless is practical in warm climates and in small households, and frequently impractical in a cold climate on a typical 200-amp service.
• Propane behaves like natural gas but the unit must be configured for it — check the model, because natural gas and propane versions are different products and converting one is a professional job, not a field swap.
• A hybrid approach is worth considering: keep your existing tank and add a small point-of-use electric unit at a distant bathroom or workshop sink. It is cheap, needs no venting, and solves the specific problem of waiting a minute for hot water at the far end of the house.

Condensing or non-condensing

Non-condensing units vent hot exhaust and are simpler and cheaper, but they require stainless steel category III venting, which is not cheap. Condensing units extract additional heat from the exhaust, which makes them more efficient and cool enough to vent through PVC or polypropylene — often cheaper to install even though the unit costs more. They also produce acidic condensate that needs draining and neutralising.

Rough guidance: if you are running a new vent, price the total installed cost both ways, because the cheaper unit is not always the cheaper job. If you are replacing an existing tankless unit and reusing its venting, match what is there.

The cold water sandwich, and minimum activation flow

Two quirks of the technology worth knowing before you own one.

The cold water sandwich happens when you turn hot water off and back on quickly. Hot water sits in the pipe, then the slug of water that was in the heater when it shut down arrives cooler, then proper hot water resumes — so you get a brief cold patch. It is most noticeable when washing dishes or in a shower where you turn the water off to soap up. Good units minimize it with a small buffer tank; cheap ones do not.

Minimum activation flow is the flow rate below which the unit will not fire at all — commonly around half a gallon per minute. A trickle from a bathroom tap may not trigger it, which means cold water. Low-flow aerators and older fixtures make this worse. If you have fixtures you use at a dribble, check the minimum activation flow in the specification.

Hard water will kill it, and the fix costs almost nothing

Scale is the leading cause of premature failure in tankless water heaters. Minerals deposit on the heat exchanger every time water passes through hot, and a scaled exchanger loses efficiency, restricts flow, and eventually triggers error codes and failure. In hard water areas this can happen in a few years.

Two things prevent it. First, buy the isolation valve kit at the same time as the heater — a pair of valves with service ports that let you circulate descaling solution through the unit. Fitting them during installation costs very little; retrofitting them later means cutting pipe. Second, flush the unit annually with the descaling solution the manufacturer specifies. It takes about an hour with a small pump and a bucket, and it is the difference between a heater that lasts fifteen years and one that lasts five. If your water is very hard, a softener or scale-inhibiting system upstream is worth considering.

Be realistic about the savings

Tankless heaters are more efficient than storage tanks, because a tank loses heat continuously to the room whether you use hot water or not, and a tankless unit uses energy only when water flows. That saving is real but modest, and the installation cost is high. If you are buying purely on a payback calculation, the numbers are usually unpersuasive.

The honest reasons to buy one are: endless hot water, so nobody gets the short end of a morning; a much smaller footprint, which frees up a closet or a corner of a garage; and a considerably longer service life than a tank — commonly quoted at around twenty years against ten to fifteen, provided it is descaled. If those matter to you, buy one. If the pitch that sells you is a lower energy bill, temper your expectations.

The 6 best tankless water heaters

1. Rheem RTG 8.4 GPM Natural Gas — best overall

Rheem is one of the largest water heater manufacturers in North America, which in this category matters more than it does in most: when a plumbed-in appliance faults in year seven, what you need is a brand whose parts are on the truck and whose error codes any local plumber recognizes. Rheem qualifies, and this non-condensing natural gas unit is its mainstream whole-house offering.

At 8.4 gallons per minute at its rated rise it is sized for a large household — apply the arithmetic from earlier in this guide and in a temperate climate that is comfortably two showers plus a kitchen tap. Customer rating is 4.8 stars, which is remarkable for a product category where installation problems routinely drag ratings into the low fours.

Why it made the list: that rating, on this kind of product, is the strongest single signal on this page. Combined with genuine national service coverage and enough capacity for a real family, it is the unit to buy if you have natural gas and want the lowest-risk purchase. Non-condensing also means no condensate drain to arrange, which simplifies some installations.

What you give up: non-condensing means it needs stainless steel category III venting, which is expensive — get the venting quoted before you compare it against a condensing unit, because the cheaper box is not always the cheaper job. It is also less efficient than a condensing design, so the running cost is slightly higher. A unit of this output requires properly sized gas supply; half-inch pipe will not feed it, and that upsizing is a real cost. Buy the isolation valve kit at the same time, because retrofitting it later means cutting pipe. And make sure you are ordering the natural gas version if that is what you have — the propane model is a different product.

Who it is for: larger households on natural gas, anyone replacing a tank in a home with an existing gas supply, and anyone who wants the safest choice rather than the cleverest.

See the Rheem RTG 8.4 GPM on Amazon →

2. Rinnai V53DeN — best compact gas unit

Rinnai did more than anyone to establish tankless water heating in North America, and the V series is its straightforward, compact, sensibly priced line. This is the unit for a home that does not need 8 gallons a minute — a two-bathroom house in a temperate or warm climate, a small family, or a household where the realistic worst case is one shower and a tap.

Compact matters in this category. Part of the appeal of going tankless is reclaiming the space a tank occupied, and a smaller unit mounts neatly on a wall in a garage or utility area without dominating it. Rinnai’s reputation for longevity is well earned and its dealer network is strong. Customer rating is 4.3 stars.

Why it made the list: it is the right size for a large number of homes, from a brand that has been building these longer than most. Buying more capacity than you need is the second most common mistake in this category after buying less, and this is the pick that says so.

The part that annoys people: it is a modest-output unit, so run the temperature rise arithmetic carefully — in a cold climate in winter this will not support two simultaneous showers, and expecting it to is how people end up disappointed. Like the Rheem it is non-condensing, so category III stainless venting is required. Rinnai’s higher-end models with recirculation sit at lower customer ratings, which is worth knowing if you are tempted to move up the range on brand loyalty alone. And it is the natural gas version; check before ordering if you are on propane.

Who it is for: one and two-bathroom homes, warm and temperate climates, small households, and anyone whose priority is reclaiming the space a tank took up.

See the Rinnai V53DeN on Amazon →

3. Westinghouse 7.9 GPM Gas — best gas unit with app control

Two things distinguish this from the other gas units here. The first is WiFi with app and voice control, which sounds like a novelty and is actually useful on a tankless heater: being able to see error codes, adjust the set temperature without going out to the garage, and get a notification when something faults is a genuine improvement over a small LED display behind a panel.

The second is the temperature stability claim — Westinghouse quotes control to within one degree Fahrenheit, achieved by self-modulating the burner as flow changes. That directly addresses the most common day-to-day complaint about tankless heating, which is the temperature wobbling when someone else opens a tap. At 7.9 gallons a minute it has close to the capacity of the Rheem. Customer rating is 4.3 stars.

Why it made the list: it targets the experience rather than the specification. Tight modulation is what makes a tankless shower feel like a tank shower, and remote diagnostics on an appliance mounted in a garage or a crawlspace is worth more than it appears. For a technically-minded owner who wants to see what the unit is doing, this is the pick.

Where it disappoints: Westinghouse in this category is a licensed brand name rather than the original manufacturer, so the service network behind it is not comparable to Rheem’s or Rinnai’s — that matters in year eight, and it is the main reason this is not the top pick. App-connected appliances also depend on the manufacturer continuing to run a cloud service; if that ends, you have a good heater with a dead app. It requires the same gas sizing and venting work as any unit of this output. And a one-degree stability claim is a manufacturer figure, so treat it as an indication of design intent rather than a measured guarantee.

Who it is for: larger households that want remote monitoring, anyone whose heater lives somewhere inconvenient, and anyone bothered by temperature fluctuation.

See the Westinghouse 7.9 GPM on Amazon →

4. Stiebel Eltron Tempra 29 Plus — best whole-house electric

If you have no gas supply, or no desire to deal with venting and combustion air, this is the serious electric option. Stiebel Eltron is a German manufacturer that has specialised in electric water heating for decades, and the Tempra Plus line is the range that made whole-house electric tankless credible in North America.

Its defining feature is flow-proportional power control: rather than switching elements on and off in steps, it modulates continuously and, if you draw more flow than it can heat to your set temperature, it reduces flow slightly rather than letting the temperature drop. That is the right behavior — a slightly weaker shower is far better than a cold one. No venting is required, it mounts flat on a wall, and there is no combustion to go wrong. Customer rating is 4.4 stars.

Why it made the list: for an all-electric home it is the best answer here, and the flow-limiting behavior is a truly superior design choice rather than a marketing point. The absence of venting also makes installation far simpler and cheaper on the plumbing side, and opens up locations a gas unit cannot use.

The drawbacks: the electrical requirement is substantial. A unit in this class needs hard-wired 240-volt service with multiple double-pole breakers and heavy cable, and many homes need panel or service work first — have an electrician quote that before you buy, because it can exceed the cost of the heater. In a cold climate at an 80-degree rise, even this unit’s output supports roughly one good shower rather than two, so run the arithmetic honestly. Electricity generally costs more per unit of heat than natural gas, so running costs will be higher where both are available. And Stiebel Eltron is a premium brand with premium pricing and a smaller North American service footprint than Rheem.

Who it is for: all-electric homes, houses with no gas supply, warm and temperate climates, and anyone who wants to avoid venting entirely.

See the Stiebel Eltron Tempra 29 Plus on Amazon →

5. ThermoMate 14kW Electric — best value electric

Not every household needs a whole-house unit sized for two simultaneous showers, and this is the pick that acknowledges it. At 14 kilowatts and a quoted 3.4 gallons a minute it is aimed at small households in warm climates, apartments, cabins, and homes where the realistic demand is one shower and a tap.

Two design details are worth noting. It uses a cast housing for the heating chamber rather than a plastic one, which is the component most likely to eventually seep on cheap electric units. And it is self-modulating, adjusting power to the flow rather than running full-tilt and overshooting. Customer rating is 4.3 stars.

Why it made the list: it fills the gap between a point-of-use unit and a premium whole-house one. For a one-bathroom home in a warm climate, a 14kW unit is sufficient, and paying several times more for capacity you will never use makes no sense. It is also a reasonable choice for a cabin, a guest house or an apartment where a tank is taking up a closet you want back.

The catch: 3.4 gallons a minute is at a modest temperature rise — in a cold climate this is a one-fixture unit and no amount of optimism changes that. 14 kilowatts at 240 volts still means a serious electrical circuit, typically two double-pole breakers and heavy cable, so have an electrician confirm your panel can take it. ThermoMate is a smaller brand than the others here, which means less certain long-term parts availability and support — a real consideration for something plumbed into a wall. And as with any electric unit, running costs are higher than gas where gas is available.

Who it is for: one-bathroom homes, warm climates, apartments, cabins and guest houses, and anyone who has done the arithmetic and found they need less than the marketing assumes.

See the ThermoMate 14kW on Amazon →

6. CAMPLUX 6kW Point-of-Use — best for a single sink

This is the pick that solves a specific and very common problem cheaply: a sink a long way from the water heater, where you run the tap for a minute before anything warm arrives. A small 240-volt unit installed under that sink heats water on demand at the point you use it, and the wait disappears.

At about eleven inches by seven and two and a half inches deep it fits inside a vanity cabinet, and it is self-modulating so it adjusts to flow rather than scalding you at low draw. It is not a whole-house device and does not pretend to be. Customer rating is 4.3 stars.

Why it made the list: because for a lot of people this is the right purchase rather than a whole-house replacement. A remote bathroom, a garage or workshop sink, a basement utility sink, a wet bar, a detached office — all of these are solved by a small point-of-use unit for a fraction of the cost and complexity of replacing your main heater. It also works alongside an existing tank rather than replacing it, which keeps the project small.

Where it falls short: 6 kilowatts is enough for a hand basin, not a shower — at a meaningful temperature rise the flow it can heat is small, so do not buy this for a bathtub. It still needs a dedicated 240-volt circuit, which means an electrician and space in your panel; the 120-volt point-of-use units you will also see are weaker again. Minimum activation flow matters here: a very gentle trickle may not fire it. Space inside a vanity is often tighter than it looks once you account for the trap and the shut-off valves, so measure. And CAMPLUX is a budget brand, so treat it as a several-year appliance.

Who it is for: a remote bathroom or utility sink, a workshop, a garage, a wet bar, and anyone who wants to fix one annoying tap rather than re-plumb the house.

See the CAMPLUX 6kW point-of-use on Amazon →

Living with a tankless heater

• Flush it every year with the manufacturer’s descaling solution, or every six months if your water is very hard. This is the single thing that determines whether you get five years or twenty.
• Fit isolation valves at installation. Without them, flushing means cutting pipe. With them, it is an hour with a pump and a bucket.
• Clean the inlet screen. Most units have a small filter at the water inlet that collects debris and restricts flow. Owners forget it exists and then diagnose a failing heat exchanger.
• Check the venting terminal outside once a season for birds’ nests, debris and snow. A blocked vent on a gas appliance is a genuine hazard.
• Write down the error codes when they appear, along with what you were doing. Intermittent faults are diagnosed from patterns, and “it flashed something” is not a pattern.
• Set the temperature once and leave it. Around 120 F is the sensible default; raising it to compensate for a sizing problem increases scald risk without solving the problem.
• Know how to shut off the gas and the water. Find both valves and label them before you need them in a hurry.
• Test your carbon monoxide alarms on a schedule, and replace them at the end of their stated service life.

Where people go wrong

• Buying on the headline GPM figure. It applies at one temperature rise, and probably not yours. Read the flow chart.
• Assuming your existing gas line and vent will work. They usually will not. Get both assessed before ordering.
• Ignoring your electrical service on an electric unit. A panel upgrade can cost more than the heater.
• Skipping the isolation valve kit. Cheap now, expensive later.
• Never descaling. The leading cause of premature failure, and entirely preventable.
• Setting the temperature high to mask undersizing. It raises scald risk and does not fix the flow problem.
• Buying the propane model when you have natural gas, or vice versa. They are different products and cannot be swapped in the field.
• Treating it as a DIY project because the box makes it look simple. Gas, venting and high-current electrical work are all licensed trades for good reasons.
• Expecting a fast payback. Buy it for endless hot water, space and service life, not for the energy bill.

Frequently asked questions

Do tankless water heaters really never run out of hot water?

They cannot run out in the way a tank does, because there is no reservoir to empty — a correctly sized unit will supply hot water indefinitely. What they can do is run out of capacity: if you ask for more flow than the unit can heat to your set temperature, the water gets cooler rather than stopping. So “endless hot water” is true at or below the unit’s rated flow for your temperature rise, and misleading above it. This is why sizing matters more than anything else.

How much will I actually save?

Really less than the marketing implies. A tankless unit eliminates the standing heat loss of a tank, which is a real but modest saving, and the installation cost is high. If gas prices and your usage are favourable the payback period is typically measured in many years. The stronger arguments are endless supply, the space you reclaim, and a service life commonly around twenty years against ten to fifteen for a tank.

Can I install one myself?

An electric point-of-use unit is within reach of a competent DIYer working with an electrician for the circuit. A whole-house gas unit is not: it involves gas line sizing, dedicated venting, combustion air and usually permits and inspection, and errors can put carbon monoxide into your home. A whole-house electric unit avoids the combustion risks but needs high-current wiring that belongs to an electrician. Check your local code, which in many places requires licensed work and inspection regardless of your skills.

What is the cold water sandwich?

When you turn hot water off and quickly back on, you get hot water from the pipe, then a brief cooler slug that was sitting in the heater when it shut down, then proper hot water. It is most noticeable when you cycle the tap frequently. Units with a small internal buffer tank reduce it; cheaper units do not. It is a characteristic of the technology rather than a fault.

Do I need a water softener?

Not necessarily, but in a hard water area a softener or scale-inhibiting system meaningfully extends the life of the heat exchanger and reduces how often you need to descale. At minimum, fit isolation valves and flush annually. If your water is very hard and you are already replacing your heater, treating the water is worth pricing at the same time.

Can a tankless heater work with a recirculation pump?

Some models are designed for it, and a few include it. Recirculation keeps hot water moving in the pipes so it arrives quickly at distant taps, which is a real convenience — but it costs energy, because you are keeping a loop of pipe warm, which partly undoes the efficiency advantage of going tankless. A timer or an on-demand button rather than continuous circulation is the sensible compromise. Not every unit supports it, so check before assuming.

What temperature should I set it to?

Around 120 F suits most households. It is hot enough for showers and washing up, and it keeps scald risk low — which matters particularly with young children, older adults, or anyone with reduced sensation. Unlike a storage tank, a tankless heater holds essentially no standing water, so the reason tanks are often set to 140 F does not apply in the same way. If someone in your home is at particular risk of scalding, ask your plumber about thermostatic mixing valves at the fixtures.

How long do they last?

Commonly quoted at around twenty years, against ten to fifteen for a storage tank — but that figure assumes annual descaling. A unit in a hard water area that is never flushed can fail in a handful of years. Maintenance is the variable, not the brand.

If you only read one section

Before choosing anything, do the arithmetic: add up the flow you want to run simultaneously, subtract your coldest incoming water temperature from your target, and read the manufacturer’s flow chart at that temperature rise. That number, not the one in the product title, is what you are buying.

With natural gas and a full-size household, the Rheem RTG 8.4 GPM is the lowest-risk choice here — ample capacity, a 4.8-star record, and a service network that will still exist in a decade. For a smaller home or a warm climate, the Rinnai V53DeN is the right size and a brand that has been doing this longest. If you want remote monitoring and tight temperature control, the Westinghouse 7.9 GPM.

Without gas, the Stiebel Eltron Tempra 29 Plus is the best whole-house electric option and its flow-limiting behavior is the right design. For a smaller all-electric household, the ThermoMate 14kW covers it for much less. And if your real problem is one distant tap, the CAMPLUX 6kW point-of-use fixes it for a fraction of the cost of replacing your main heater — which is often the smartest purchase on this page.

Whichever you choose, budget for the installation before the unit, buy the isolation valve kit at the same time, and put an annual descale in the calendar. Those three decisions determine whether this is a fifteen-year appliance or a five-year one.

For more on your home’s systems, see our guides to the best water filters, the best smart thermostats, and the best space heaters.

Also worth reading: our guide to the best shower heads.

Also worth reading: our guide to the best water softeners.

Also worth reading: our guide to the best bidets.