Short answer: the Rheem RTEX-24 is the best tankless water heater for whole house use we cover this year, the MIZUDO 120,000 BTU gas model is the pick if you want app control and indoor or outdoor flexibility, and the Ranein 4.3 GPM propane unit is the value choice with the largest owner-feedback record among the gas models here. The other decision that matters more than brand is fuel type: gas recovers from a cold inlet far better, while electric avoids venting entirely but can force a 200-amp electrical upgrade.
Our team spent several weeks reading spec sheets, warranty terms, and verified buyer reviews across ten whole-house models, then compared them on the only metrics that decide whether a unit works in a real home: flow rate at a given inlet temperature, heating capacity, warranty depth, and how hard the installation actually is. The Rheem RTEX-24 leads because it pairs the widest verified review base in the group with a footprint that frees an entire utility room wall, and it needs no vent.
The rest of this guide covers the ten best options in detail, then the sizing math, fuel tradeoffs, and installation realities that decide whether any of them fit your house. Every figure below comes from the manufacturer listing and the verified buyer review record, so you can check my work before you commit.
Table of Contents
- Top 3 Picks for Best Whole-House Tankless Water Heaters (October 2026)
- All 10 Whole-House Tankless Water Heaters at a Glance in 2026
- How We Picked These Whole-House Tankless Water Heaters
- 1. Rheem RTEX-24 24kW Electric Tankless Water Heater – Best Overall
- 2. MIZUDO 120,000 BTU Natural Gas Tankless Water Heater – Best App Control
- 3. Stiebel Eltron Tempra 20 Trend 19.2kW Electric – Best for Smaller Homes
- 4. ThermoMate CZ422NG 5 GPM Natural Gas – Best Safety Suite
- 5. Rheem RTG-70DVLN-3 7.0 GPM Gas – Best for Large Homes
- 6. CAMPLUX CA528WNG 150,000 BTU Gas – Best for Tight Utility Rooms
- 7. APUS AP-AWH-Q20NG 140,000 BTU Gas – Best for Instant Hot Water
- 8. Ranein 4.3 GPM Propane – Best Value for Off-Grid Homes
- 9. FOGATTI InstaGas Comfort 120,000 BTU – Best for Low-Pressure Homes
- 10. APUS AP-AWH-Q13NG 95,000 BTU – Budget Pick
- How to Size a Tankless Water Heater for Your Whole House
- Gas vs Electric vs Heat Pump Water Heaters for a Whole Home
- Condensing vs Non-Condensing Tankless Units
- What Plumbers Wish You Knew Before You Buy
- When Not to Go Tankless
- Installation, Venting, and Recirculation Loops
- Maintenance: Descaling, Filters, and Hard Water
- Frequently Asked Questions
- What is the best tankless water heater for a whole house?
- How big of a tankless water heater do I need for a 2000 square foot house?
- What do plumbers say about tankless water heaters?
- What are two disadvantages of a tankless water heater?
- Will I save money with a tankless water heater?
- Does a tankless water heater work during a power outage?
- The Best Tankless Water Heaters for Whole House Use in 2026
Top 3 Picks for Best Whole-House Tankless Water Heaters (October 2026)
Rheem RTEX-24 24kW Electric
- 5.9 GPM from 24kW
- 1-degree temperature control
- No venting required
MIZUDO 120,000 BTU Gas
- 5.1 GPM with WiFi app
- Indoor or outdoor convertible
- ±1 F stability
Ranein 4.3 GPM Propane
- 4.3 GPM for 3 to 4 fixtures
- 4 preset operating modes
- 710 verified reviews
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Those three cover very different households. The Rheem handles the largest electrical demand in the group and never runs out of hot water mid-shower. The MIZUDO is the only unit here whose manufacturer lists an indoor and outdoor convertible chassis, which matters if your only warm wall is an exterior one. The Ranein runs on propane rather than natural gas, so it suits rural homes where natural gas is not available.
All 10 Whole-House Tankless Water Heaters at a Glance in 2026
| Product | Specifications | Action |
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Rheem RTEX-24 24kW Electric
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Check Latest Price |
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MIZUDO 120,000 BTU Natural Gas
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Check Latest Price |
Stiebel Eltron Tempra 20 Trend 19.2kW
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Check Latest Price |
ThermoMate CZ422NG Natural Gas
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Check Latest Price |
Rheem RTG-70DVLN-3 Natural Gas
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Check Latest Price |
CAMPLUX CA528WNG Natural Gas
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Check Latest Price |
APUS AP-AWH-Q20NG Natural Gas
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Check Latest Price |
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Ranein 4.3 GPM Propane
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Check Latest Price |
FOGATTI InstaGas Comfort Natural Gas
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Check Latest Price |
APUS AP-AWH-Q13NG Natural Gas
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Check Latest Price |
We earn from qualifying purchases. CERTAIN CONTENT THAT APPEARS ON THIS SITE COMES FROM AMAZON. THIS CONTENT IS PROVIDED 'AS IS' AND IS SUBJECT TO CHANGE OR REMOVAL AT ANY TIME.
Read the fuel column first. Seven of the ten burn gas, two are electric, and one runs on propane. Gas units carry BTU ratings and need venting; the electric units carry kilowatt ratings and need a heavy circuit. Only the MIZUDO is described by its manufacturer as convertible between an indoor and an outdoor install, and that conversion needs a manufacturer vent cap kit.
Flow rate is the second column that decides fit. In this group the ratings run from 2.01 GPM on the Stiebel Eltron up to 7.0 GPM on the Rheem RTG. Anything at or below 4.5 GPM is a two-bathroom home at best. If you have three or more bathrooms plus a laundry washer running while a shower runs, start at 6 GPM.
How We Picked These Whole-House Tankless Water Heaters
We ranked these on four things, in this order. First is verified buyer feedback, because a spec sheet tells you what a manufacturer claims while review data tells you what a household actually experienced after a year of use. Second is heating capacity matched to realistic whole-house demand rather than the maximum number on the box. Third is warranty depth, with the heat exchanger weighted most heavily since it is the part that fails. Fourth is installation realism: electrical requirements, vent diameter, included fittings, and elevation limits.
We deliberately kept both gas and electric models in the mix, even though most competing roundups pick a single fuel type. A home with no gas supply and a 200-amp panel has a completely different answer than a home with a gas line and a 40-amp-fed panel, and a list that only covers one of them is not useful to half the readers.
We also excluded nothing on brand name alone. A lesser-known brand with a documented two-year unit and five-year heat exchanger warranty can be a better purchase than a famous name whose warranty is voided by a DIY install. What we would not do is pretend a 66-review listing tells the same story as an 894-review one, and we flag that difference throughout.
1. Rheem RTEX-24 24kW Electric Tankless Water Heater – Best Overall
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray
- 24kW, 5.9 GPM
- Setpoint 80-140 F in 1 degree steps
- No venting
- 200A panel, three 40A breakers
Pros
- Wall-mount body about 90 percent smaller than a tank heater
- 5.9 GPM of continuous hot water from 24kW
- Temperature adjustable in 1 degree steps from 80 to 140 F
- No venting required so the install is simpler than gas
- Buyers report six-plus years with no failures
Cons
- Needs a 200-amp panel plus three 40-amp double-pole breakers
- 24kW is short for full baths when inlet water is very cold
- Display reads higher than actual water at distant fixtures
- No hot water at all during a power outage
The RTEX-24 is the pick I kept coming back to while comparing the field, and the reason is the 894-review record. That is far more verified feedback than most of the gas models here, which means the failure patterns are well documented rather than anecdotal. Owners across those reviews describe the same thing: a wall-mounted box about the size of a large suitcase, and hot water that simply never stops.
At 24 kW it puts out 5.9 GPM, which is enough to run two showers and a laundry load without the outlet temperature dropping. Control runs in 1-degree increments from 80 to 140 F on an LED display, and the digital thermostat holds the setpoint far more tightly than a gas valve at low flow. There is no vent, no flue, and no condensate line, so the install is essentially a plumbing and electrical job.
The hard requirement is electrical. The unit needs 240V single-phase power, three sets of number 8 AWG copper with ground, three 40-amp double-pole breakers, and a recommended minimum 200-amp household service panel. If your home runs on a 100-amp panel from an older build, the electrical work becomes the largest line item in the project, and that is the single most common complaint in the reviews.
Two other patterns show up. In cold northern climates, buyers report 24kW comfortably runs a shower but will not fill a bathtub at full flow, because the unit has to work harder to lift very cold supply water. And a few owners note the panel reads a few degrees higher than the water arriving at a distant fixture, which is a sensor artifact rather than a real temperature swing.
What you need to check before ordering
Ask your electrician for your service panel rating and whether it has breaker space for three double-pole 40-amp circuits. If the answer is no, budget for a sub-panel or a service upgrade before you order the heater, because the unit itself is the easy part. A few buyers also shipped units with a faulty control board or thermostat and needed an exchange, so keep the packaging until the unit has run a full cycle.
Where this unit falls short
There is no stored hot water, which means a power outage means no hot water at all until power returns. That is the tradeoff every electric tankless carries, and it is a real one in homes where outages are common or where the family relies on an electric well pump. In a cold-climate house with a large family and a tub-filling habit, 24kW is the wrong size and a larger electric model would be the right call.
2. MIZUDO 120,000 BTU Natural Gas Tankless Water Heater – Best App Control
MIZUDO 120,000 BTU Natural Gas Tankless Water Heater,Max 5.1 GPM,WiFi&APP
- 120,000 BTU, 5.1 GPM
- WiFi and app control
- ±1 F stability
- Indoor or outdoor convertible
Pros
- WiFi and app control for temperature
- energy use
- and maintenance alerts
- Convertible indoor or outdoor mounting with accessory kits
- Holds output within about 1 F through flow monitoring and gas modulation
- CSA certified with freeze
- dry burn
- flame failure
- and exhaust blockage protection
- Silent running with a bright LED display
Cons
- Vent pipe and gas fittings are not included
- 5.1 GPM fills tubs slowly
- Not rated above 2000 feet elevation
- Some reports of error codes and 60 to 90 second bursts of hot water
The MIZUDO is one of only two units in this roundup with real app control, and the one with the more complete feature set. The built-in WiFi and app let you change the setpoint, watch energy consumption, and receive maintenance alerts from your phone, and the app is what tipped this one into my list for anyone who likes to see how their utilities are trending. Most owners install it in place of a 40-gallon tank and report fast, steady delivery for a shower and a sink together.
Temperature stability is the technical headline. Water flow monitoring and gas modulation hold the output within about 1 F even when another fixture opens mid-shower, and the 120,000 BTU burner with a phosphorus-deoxidized copper heat exchanger and stainless steel combustion chamber is a conventional, serviceable design. At 5.1 GPM it is a mid-size output, which is plenty for two bathrooms and short of what a three-bath house wants.
The indoor or outdoor convertible chassis is genuinely useful. For an indoor install you need a 3-inch OD vent pipe; for an outdoor install the manufacturer supplies a vent cap conversion kit. Freeze protection, dry burn prevention, flame failure detection, and exhaust blockage protection are all standard on this chassis, which matters more than it sounds in a garage or exterior wall mount.
The practical catches are physical. Gas and water fittings and the vent hardware are not in the box, so those are extra line items on the install. The unit is not rated for installation above 2,000 feet elevation, which voids the warranty in high-desert areas. And a minority of owners report repeated error codes followed by 60 to 90 second bursts of hot water before shutdown, most often in very cold or high-altitude installations.
What you need to check before ordering
Measure your elevation and confirm you are inside the 2,000 foot limit, then decide indoor or outdoor before you buy, because the vent hardware is different. The warranty runs 2 years on the full unit and 5 years on the heat exchanger, so ask your installer in writing whether the flue sizing affects that coverage. The included components are the heater, an outdoor fume hood, manual, quick installation poster, assembly kit, and warranty card.
Where this unit falls short
Five GPM is the ceiling, and a family that fills a tub while running a shower will notice the difference between this and a 7 GPM gas model. The app is a genuine convenience but adds a failure surface: if the WiFi module is the problem, the heater itself is fine and the module may not be a separately serviceable part. Owners on steep, cold sites also report the freeze protection is only a comfort, not a guarantee.
3. Stiebel Eltron Tempra 20 Trend 19.2kW Electric – Best for Smaller Homes
Stiebel Eltron Tempra 20 Trend Electric Tankless Water Heater, 19.2kW, 240V
- 19.2kW, 2.01 GPM
- Solid copper heating
- Output 68-140 F
- 7 year leakage warranty
Pros
- Made in Germany with a solid copper heating system
- 7-year leakage warranty and 3-year parts coverage
- Silent operation with a clear digital temperature display
- Output adjustable from 68 to 140 F
- Auto-modulation trims energy use when no hot water is being drawn
Cons
- 2.01 GPM is the lowest flow rating in this group
- Needs hard wiring and a minimum 125 A service
- Tub fills and multiple showers take noticeably longer
The Tempra 20 Trend is the pick for a house with one and a half or two bathrooms, a gas-free lot, and no appetite for a vent. Owners describe it as a well-made German unit that handles standard whole-home demand, and the review themes are about build quality, quiet running, and easy temperature control rather than raw capacity. That is the right way to think about it: this is a small, tidy, dependable heater, not a high-output one.
At 19.2 kW and 2.01 GPM it is the lowest-output electric unit here. Output temperature is adjustable from 68 to 140 F, the heating system is solid copper with an electronic switch, and a digital display shows the setpoint. Electrical requirements are lighter than the Rheem RTEX-24: two 40-amp breakers, an 80-amp draw, and a minimum recommended service of 125 amps, so it can often go in on a panel that cannot take the larger electric unit.
No venting is required, the body is a compact wall-mount at 16.63 by 14.5 by 4-5/8 inches, and the unit weighs 16.1 pounds, which makes a one-person install realistic. Auto-modulation trims energy use whenever hot water is not being drawn, and the manufacturer rates savings up to 34 percent in whole-home use compared with a conventional tank setup.
Be realistic about the flow rating. Two GPM is enough for a single shower at a comfortable temperature or a couple of low-flow sinks, and it is the reason we did not put this higher in the list for a family home. If your household is three people with two full bathrooms, the 24kW class electric units are the better fit even though this one has the better warranty.
What you need to check before ordering
Confirm your electrical service is at least 125 amps and that it has room for two double-pole 40-amp breakers. Because it is hard-wired, this is not a plug-in job, and the installation must be done to code. The included pressure rating is listed at 19.5 kilopascals, which is noticeably lower than the 150 psi figure most tankless units carry, so check your home’s supply pressure is within range.
Where this unit falls short
The 2.01 GPM rating is the whole caveat. Multiple owners say tub fills and any attempt at two simultaneous showers take noticeably longer than they would on a larger electric model. The 103-review record is healthy but thin compared with the Rheem, and the 19.2kW configuration sits at the bottom of the Tempra range rather than at the top of it.
4. ThermoMate CZ422NG 5 GPM Natural Gas – Best Safety Suite
ThermoMate CZ422NG, Natural Gas Tankless Water Heater Indoor, Up to 5 GPM
- 5 GPM, 113,000 BTU
- ±1 F control
- 0.81 UEF
- Nine CSA protections
Pros
- Compact 21 x 13 x 7 inch wall-mount body
- 5 GPM at 113000 BTU holds two showers at 105 F
- Flow sensor and control chip adjust 20000 times per second for ±1 F stability
- CSA certified with nine listed protections including timeout and pipe blockage
- 3.5-inch LED display shows flow
- fan
- and flame status
Cons
- 5 GPM is enough for two showers but thin for quick tub fills
- Outlet temperature drops in very cold supply water
- Error codes take some learning to read
The CZ422NG stands out for one reason: its safety list. It is CSA certified with boil-dry, freeze, flame-out, overheat, over-temperature, timeout, pipe blockage, high-temperature lock, and excessive air pressure protection, which is the broadest protection set any gas unit in this roundup lists, and for a household with young children or an older relative, that list is worth reading before you compare anything else.
Performance is solid rather than exceptional. The 113,000 BTU burner delivers 5 GPM and holds 105 F from a 65 F inlet, so two showers running together stay comfortable. The oxygen-free copper heat exchanger is rated at up to 98 percent thermal efficiency with a UEF of 0.81, and the flow sensor and control chip adjust heating 20,000 times per second to keep temperature within about 1 F.
Installation is refreshingly conventional. It uses 3/4-inch NPT water connections, a 1/2-inch NPT gas inlet, a 3-inch OD vent, and a UL-approved 120V plug, so it hooks into most existing gas tank locations without resizing the plumbing. The DC high-speed fan is rated at 360 pascals of static pressure and 3000 RPM, which owners say evacuates the exhaust even in strong wind. Freeze protection engages at 41 F, and a 3.5-inch LED display gives you flow, fan, and flame status plus error codes.
The main reservation is raw flow. Five GPM covers two showers but is thin for filling a bathtub quickly, and at a 35 F rise the outlet temperature drops noticeably in cold-water households. The diagnostic display is genuinely useful but it does mean you will be learning a code list rather than reading a simple status light.
What you need to check before ordering
Verify your existing gas line and vent size can carry a 3-inch OD vent and a 1/2-inch NPT gas inlet, and confirm the 150 psi maximum pressure matches your supply. Freeze protection activates at 41 F, so in an unheated garage you are relying on that feature or on draining the unit, not on the appliance surviving a hard freeze. The unit is 22 pounds and mounts on a wall.
Where this unit falls short
There is no condensing section and no condensate drain, so this is a non-condensing design and you give up the efficiency a condensing unit recovers from the exhaust. Error codes are the main diagnostic tool, and a few owners find that unhelpfully terse when something trips at 2 a.m. Buyers who need more than two simultaneous fixtures should look at the 7 GPM Rheem instead.
5. Rheem RTG-70DVLN-3 7.0 GPM Gas – Best for Large Homes
Rheem RTG Series 7.0 GPM Natural Gas Tankless Water Heater Indoor | 160,000 BTUs High Efficiency On Demand, Continuous Hot Water | Non-Condensing
- 7.0 GPM, 160,000 BTU
- 0.82 UEF
- LeakGuard detection
- 15 year heat exchanger
Pros
- 7.0 GPM at a 35 F rise covers two to three simultaneous showers
- 0.82 UEF with up to 34 percent savings versus a 50-gallon electric tank
- Digital LED control panel with 1 F adjustments
- LeakGuard leak detection and prevention
- 15-year heat exchanger warranty
Cons
- Weighs 46.5 pounds
- which makes mounting more involved
- Needs a direct vent and a properly sized gas line
- Only 66 reviews so long-term data is thin
If your house has three or more bathrooms, this is the one I would size up to. At 7.0 GPM and 160,000 BTU it is the highest-output unit in the roundup, and at a 35 F temperature rise it is the one here rated to cover two to three showers at once plus a laundry load. Owners cite strong simultaneous-flow capacity and noticeably lower energy use after replacing a tank heater.
The Rheem name matters here in a way it does not for the smaller units. This chassis carries a 15-year heat exchanger warranty, 5 years on parts, and 1 year on labor, which is the deepest heat exchanger coverage of any model on this list. LeakGuard leak detection is built in, freeze and flame failure protection are standard, and the digital LED panel adjusts temperature in 1 F steps with hot-start programming.
It is also friendly to older homes in ways competitors are not. Universal venting compatibility means it can reuse more of an existing flue, and it is compatible with a 1/2-inch gas line, so homes with a reduced gas line size are not automatically excluded. The 0.82 UEF is the highest in the group, and the manufacturer rates up to 34 percent savings in energy costs against a 50-gallon electric tank heater.
What gives me pause is the review base. Sixty-six reviews is the thinnest in this roundup, which means you are buying on a proven brand name and a long warranty rather than on a deep body of owner data. The unit also weighs 46.5 pounds, more than any other model we covered, and mounting it high on a wall takes two people and a plan.
What you need to check before ordering
Have your gas supplier confirm the meter and regulator can deliver 160,000 BTU of input; older gas meters are the usual bottleneck. This is an indoor direct vent installation, so confirm the flue location and length before the unit is on a truck. The dimensions are 13.5 by 24.2 by 10.27 inches, which is taller than most tankless bodies.
Where this unit falls short
High output is not the same as forgiving installation. You need a properly sized gas line, a real vent run, and adequate wall structure for 46.5 pounds. Buyers in cold regions should note the rating assumes a 35 F rise; with colder supply water the effective output falls. And if the manufacturer warranty requires professional installation, a DIY swap could cost you the 15-year coverage that makes this unit worth buying.
6. CAMPLUX CA528WNG 150,000 BTU Gas – Best for Tight Utility Rooms
CAMPLUX Tankless Water Heater Natural Gas Indoor, Up to 6 GPM 150,000 BTU
- Up to 6 GPM, 150,000 BTU
- 45 dB operation
- 50 percent slimmer
- 2 year parts
Pros
- Very quiet 45 dB bottom-fan operation
- Body is 50 percent slimmer than a standard tankless unit
- Holds temperature within 0.5 C as flow changes
- US-based technical support that has shipped replacement units
- 6-layer safety protection including freeze
- dry burn
- and overheat
Cons
- Mounting brackets often do not span two studs
- All connections exit from the bottom at a slight angle
- Vent kit and fittings are not included
- Some reports of ignition failures and error codes
The CAMPLUX solves a specific problem: utility rooms where a standard tankless body will not fit. Its profile is 50 percent slimmer than a standard tankless unit, and at 33.1 pounds it is one of the lighter gas models here. The operating noise is quoted at 45 dB with a bottom-mounted fan, quieter than a refrigerator according to the manufacturer, and owners consistently single out quiet running as the reason they are happy with it.
Output is generous for the size. The unit is rated up to 6 GPM from a 150,000 BTU burner with AI-assisted efficiency of 95 percent, and the control system holds temperature within 0.5 C even as you change the volume of water mid-flow. A six-layer safety package covers freeze, dry burn, overheat, and high pressure, and the manufacturer offers free parts for 2 years with 24/7 US technical support.
What we like most is the support story. Several owners describe the company’s technical support as excellent, with replacement units shipped when a unit failed, which is not always the case with brands in this price bracket. The smart control also has power outage memory, so the setpoint survives a flicker instead of resetting.
The complaints are installation geometry rather than performance. The mounting brackets are often too narrow to span two studs, so extra blocking has to be added. All pipe and hose connections exit from the bottom at a slight angle, which complicates a hard-piped install into an existing closet. And a 3-inch vent kit plus new fittings may be required, which differ from what was on the wall before.
What you need to check before ordering
Measure the wall cavity carefully and confirm the bracket can land on studs or on blocking you will add. Plan the pipe routing around the bottom-exit connections before the drywall goes back up. Note that the listed maximum temperature of 155 F is above the 140 F used by most of this group, so check the tempering valve on your hot water distribution.
Where this unit falls short
Some units have failed to ignite and thrown error codes, requiring a replacement, and the 71-review base is thin. The listed dimensions of 14.3 by 6.5 inches describe the face of the unit rather than a full depth, so do not plan the install from that number alone. And at a 6 GPM maximum you are still one step below the 7 GPM Rheem for very large homes.
7. APUS AP-AWH-Q20NG 140,000 BTU Gas – Best for Instant Hot Water
APUS Natural Gas Tankless Water Heater, 140,000 BTU, Up to 6.8 GPM, Indoor
- 140,000 BTU, up to 6.8 GPM
- Booster pump
- About 1 second delivery
- WiFi app control
Pros
- Built-in booster pump pushes flow up to 130 percent to a maximum of 6.8 GPM
- Single-circulation design delivers hot water in about a second
- WiFi app control adjustable from 95 to 140 F
- Bottom turbo fan runs quieter than a standard tankless fan
- Vent pipe and piping accessories included in the box
Cons
- Several owners report it cannot heat a bathtub adequately
- Extra fittings and adapters usually must be bought separately
- Must be fully drained near 41 F ambient
- A 4.0 average with 21 percent one-star reviews
The APUS Q20 makes the shortest hot water wait claim of anything we reviewed, at about a second, and the mechanism is interesting: a built-in booster pump increases flow up to 130 percent, to a stated maximum of 6.8 GPM, while a single-circulation design is claimed to produce hot water in about one second. For a household that hates the wait between turning a tap and usable heat, that is the selling point.
Other owners like the app control through the Tuya app, adjustable from 95 to 140 F, and the Smart Season Comfort Mode with plus or minus 1 F control. The 140,000 BTU burner uses an oxygen-free copper heat exchanger, the UEF is listed at 0.81, and the bottom turbo fan is claimed to be 30 percent quieter than a standard tankless fan.
Now the honest part, because this is the weakest review profile in the roundup. The average is 4.0 stars with 21 percent one-star reviews, and the dominant complaint is that the unit cannot heat water adequately for a bathtub, which directly contradicts the advertised claim of two showers plus two sinks. Feedback also splits sharply: households with modest demand love the flow and the footprint, while others report they are disappointed once two fixtures are running.
Two smaller issues matter for planning. Fittings and adapters are usually bought separately even though a vent pipe and zero-cold-water piping accessories are included, and the manufacturer requires the unit to be fully drained if ambient temperature approaches 41 F, which rules out an unheated garage without extra work.
What you need to check before ordering
Do the fixture math honestly before trusting the 6.8 GPM figure, because a booster pump raises flow but does not add BTU. At 140,000 BTU you are buying less heating capacity than the 160,000 BTU Rheem, and that gap shows up in tub fills and in cold-supply conditions. Confirm the drain requirement is compatible with wherever you plan to mount it.
Where this unit falls short
The advertised performance and the owner reports do not fully agree, and that gap is the deciding factor. The single-circulation design is a manufacturer’s claim that the review record does not consistently confirm. For a family that fills a tub regularly, we would steer you to a higher-BTU non-condensing model instead.
8. Ranein 4.3 GPM Propane – Best Value for Off-Grid Homes
Ranein Propane Gas Tankless Water Heater, 4.3 GPM, 100,000 BTU, Indoor
- 100,000 BTU, 4.3 GPM
- 4 preset modes
- 95-155 F with scald lock
- Propane
Pros
- 710 verified reviews
- the largest owner record among the gas units here
- 4.3 GPM and 100000 BTU serve 3 to 4 fixtures at once
- Four preset modes including bathtub fill adjustment from 50 to 800 liters
- Wide 95 to 155 F range with a high-temperature scald lock
- Vent pipe and assembly kit included in the box
Cons
- Propane and natural gas versions are not interchangeable
- 1/2-inch connections are not tapered NPT so adapters are needed
- Settings reset to 129 F after a power cycle
- Anti-freeze protection only to about 14 F
The Ranein is the only propane model here, and that alone makes it the answer for a rural property, a cabin, or a home where natural gas is not available. It also carries 710 verified reviews, by a wide margin the largest owner record among the gas units in this roundup, which means the long-term behavior of this chassis is well documented rather than a promise on a spec sheet.
Owners who bought the correct fuel type report it runs large households, with 100,000 BTU and 4.3 GPM covering three to four water points simultaneously. Four preset modes cover Four Season, Kitchen at a 100 F default, Bathtub with fill adjustment from 50 to 800 liters, and Shower. Temperature is adjustable from 95 to 155 F with a high-temperature lock to prevent scalding, and the LED display shows real-time temperature, status, fault codes, and temperature memory.
The heat exchanger is oxygen-free copper with enhanced combustion technology, and the anti-freeze device is rated to 14 F, which is far deeper than the 41 F threshold most of the gas units here rely on. Several owners with large households report visibly lower bills after replacing a 40-gallon tank, and the original vent pipe is included in the box.
The recurring negatives are installation details. Propane and natural gas versions are not interchangeable, and a gas-type mistake is not returnable, so be certain before you order. The 1/2-inch connections are not tapered NPT, so 3/4-inch adapters and careful sealing are required. There is no app or remote, and settings reset to 129 F after a power cycle, which erases your chosen temperature.
What you need to check before ordering
Confirm the fuel type with your propane supplier before the unit ships, because the mistake is not returnable. Measure your propane line capacity, because 100,000 BTU is a meaningful load for a small tank and an undersized line will starve the burner. The listed maximum working pressure is 116 psi, and the unit is not rated for elevation above 2,000 feet.
Where this unit falls short
At 4.3 GPM this is a two-to-three-fixture appliance, not a three-bath whole-home system, and a family that showers and washes simultaneously will see the difference. The temperature memory is lost on power down, requiring a manual reset at the unit. Owners also report a modest rate of early ignition or control-board failures inside the first year, so plan on being reachable for the first season.
9. FOGATTI InstaGas Comfort 120,000 BTU – Best for Low-Pressure Homes
FOGATTI Tankless Water Heater Natural Gas Indoor On Demand CSA Certified
- 120,000 BTU, 5.1 GPM
- Water servo ±1 F
- Operates at 15 PSI
- 2 year unit
Pros
- Runs from 15 to 150 PSI supply pressure
- Water servo with four-stage combustion holds 1 F control
- High-efficiency copper heat exchanger with a 304 stainless steel burner
- About a third the space of a traditional tank heater
- CSA certified with an active anti-freeze heating device
Cons
- At low faucet flow it can output scalding 170 F water
- No vent pipe or plumbing fittings in the box
- May need the power button pressed after any power interruption
- Customer service reported as slow to respond in some cases
The FOGATTI’s distinguishing spec is its 15 PSI minimum operating pressure. That matters in older homes, in homes with a well and a pressure-reducing valve set low, and anywhere the supply pressure dips when several fixtures open.
Everything else is conventional and well executed. The 120,000 BTU burner delivers 5.1 GPM for two to four outlet points, and a water servo system with temperature sensors and four-stage combustion holds control within about 1 F. The heat exchanger is high-efficiency copper with a 304 stainless steel burner, and the body takes up roughly a third the space of a traditional tank heater at 23.9 by 15.5 by 7.3 inches.
Owners generally report a clean swap from a 40-gallon tank, steady hot water for two simultaneous showers, and low operating noise. That is the core use case and it works. The 2-year unit and 5-year heat exchanger coverage is the same structure the MIZUDO uses.
Two issues stand out. First, the box contains only the heater, manuals, an assembly kit, and a warranty card, so installers have to buy tankless valves and a 3-inch vent elbow separately. Second, a smaller group flags that at very low faucet flow the unit cannot regulate and can output water near 170 F, which is a genuine scald risk worth taking seriously if you have young children in the house.
What you need to check before ordering
Measure the actual dynamic pressure at the tank location with several fixtures running, not just static pressure at the main. Plan to purchase a 3-inch vent and tankless valves separately, and factor that into the install quote so it is not a surprise. The anti-freeze device is active heating, and the manufacturer instructs draining the unit if the temperature drops below 5 F or it will sit unused.
Where this unit falls short
The low-flow scalding behavior is the deal-breaker for some households and is the reason this unit sits below the gas models with better temperature modulation. Owners also report that the power button may need to be pressed after any power interruption before the unit restarts, and some report slow or unresponsive customer service. At 5.1 GPM it is also one step short of the larger gas models.
10. APUS AP-AWH-Q13NG 95,000 BTU – Budget Pick
APUS Natural Gas Tankless Water Heater, 95,000 BTU, 4.42 GPM Indoor
- 95,000 BTU, 4.42 GPM
- 36 dB operation
- 0.81 UEF
- 19.2 pounds
Pros
- 4.42 GPM from a 95000 BTU burner
- Starts at a low 0.66 GPM activation flow
- Up to 98 percent thermal efficiency with a 0.81 UEF
- Light at 19.2 pounds and only 5.91 inches deep
- Quiet 36 dB operation with an LED touchscreen
- Vent pipe included in the box
Cons
- 4.42 GPM is modest for high-flow homes
- Some failures show a lit display but no hot water
- Must be fully drained near 41 F ambient
- External debris can block the exhaust and trip the cutoff
The Q13 costs less than every other gas unit we reviewed, and at 4.3 stars from 139 reviews, it is not a compromise piece. Owners report quick hot water, an easy install on an existing vent, quiet running, and a noticeable drop in utility costs after replacing a tank. At 95,000 BTU and 4.42 GPM it serves two showers plus a sink according to the manufacturer, which covers most homes under 2000 square feet.
The engineering details are better than the price suggests. Low-flow start technology triggers at just 0.66 GPM, so a low-flow kitchen faucet still gets hot water rather than a cold patch. High-precision sensors and a smart CPU hold temperature within about 1 F from 95 to 140 F. The oxygen-free copper heat exchanger with segmented combustion is rated at up to 98 percent thermal efficiency and a UEF of 0.81, and the whole unit weighs just 19.2 pounds.
At 5.91 inches deep and 36 dB, it is among the lightest gas units in this roundup, and 36 dB is the lowest operating noise figure quoted here. The LED touchscreen is a step up in feel from the segment displays on the budget gas models. The manufacturer also claims 30 percent greater energy savings than conventional tank water heaters, and the vent pipe is included in the box, which removes one install line item.
The most common negative theme is a startup failure where the display powers on but the burner never fires. In those cases, owners report, the manufacturer’s support has been responsive, troubleshooting the cause and issuing replacements or credits. The unit must be fully drained if ambient temperature approaches 41 F, and the exhaust can be blocked by external debris such as insect nests, which trips the safety cutoff.
What you need to check before ordering
Check your gas line capacity against 95,000 BTU, which is a much easier ask than 160,000 BTU and often the reason this unit swaps in cleanly. Confirm the 5.9-inch depth fits your wall cavity with clearance for the vent, and decide now whether you will drain it in winter. The listed dimensions are 20.55 by 13.27 by 5.91 inches, so measure before ordering.
Where this unit falls short
At 4.42 GPM the unit is modest, and some owners report slightly reduced shower pressure in high-flow homes where total demand exceeds its output. Startup failures exist even with responsive support behind them, which is a real inconvenience. Coverage is 2 years, the shortest structure here, and a few owners note slight audible operation during heavy draw despite the low quoted decibel figure.
How to Size a Tankless Water Heater for Your Whole House
Size for the worst moment, not the average one. Add up the flow your household is likely to run at the same time, then add a margin. A low-flow faucet uses about 0.5 GPM, a dishwasher around 1 GPM, a washing machine around 1.5 GPM, and a shower between 1.5 and 2.5 GPM depending on the fixture. Two showers plus a washer is roughly 6.5 GPM, which is why the 5 GPM models feel short in a busy house.
Then adjust for inlet temperature, which is the variable most spec sheets bury. Every flow rating in this roundup assumes a 35 F temperature rise. In a Gulf Coast home where supply water is 65 F, a 5 GPM unit can hold 105 F as the ThermoMate does. In a northern winter where supply water is 40 F, the same unit delivers noticeably cooler output and you need more BTU or kilowatts to compensate.
As a rough map: a home under 1500 square feet with one full bathroom is comfortable at 3 to 4.5 GPM. A 2000 square foot house with two full bathrooms and a laundry room wants 5 to 6 GPM. A 3000-plus square foot home with three bathrooms, a laundry room, and a kitchen that runs the dishwasher at the same time as a shower needs 6.8 to 7 GPM, which is the top of this roundup.
Count fixtures rather than square footage if you can. Most sizing calculators start from the number of full bathrooms, and square footage is only a proxy for that. Our rule of thumb: add 2.5 GPM for the first full bathroom, 1.5 for the second, 1.0 for each additional half bath, and 1.5 for the laundry pair, then round up to the next available model.
Gas vs Electric vs Heat Pump Water Heaters for a Whole Home
Gas heats water faster and recovers faster. That is why every high-output model in this roundup burns fuel, and why forum threads about cold-climate performance are almost entirely about gas units. A gas heater has a burner and a copper heat exchanger, needs venting, and needs a gas line sized for the full BTU input.
Electric is simpler to install and needs no vent, but the electrical requirement is the hidden cost. The Rheem RTEX-24 needs 240V single-phase power, three 40-amp double-pole breakers, number 8 AWG copper with ground, and a 200-amp service panel. Plumbers and electricians in r/HomeImprovement and r/AskElectricians threads describe the panel upgrade as the most common surprise in electric tankless projects.
Power behavior is the sharpest difference. Every electric tankless unit here, including the Rheem and the Stiebel Eltron, has no stored hot water, so an outage means no hot water until power returns. Gas units behave differently: they need 120V power for controls and the fan, so most shut down without electricity too, but the firebox and its safety systems are designed around that loss. A heat pump water heater is a third option for all-electric homes, storing and reheating water rather than heating on demand.
Condensing vs Non-Condensing Tankless Units
A condensing unit recovers heat from the exhaust, which pushes efficiency higher and requires a PVC drain line for the condensate. A non-condensing unit sends hot exhaust straight up a metal flue and is simpler and cheaper to vent, which is why most of the gas models in this roundup, including the Rheem RTG and the ThermoMate, are non-condensing.
For most whole-house replacements, the difference does not justify chasing a condensing unit. Condensing matters most when you have a long vent run, a high-efficiency goal, or a cold climate where the extra heat recovery pays for the extra plumbing. In warm regions with a short existing flue, non-condensing is the pragmatic choice and it is what the majority of owners in our review set actually installed.
What Plumbers Wish You Knew Before You Buy
Local parts and service availability is the number one thing that shows up in plumbing forums, and the consensus in r/Plumbing and r/askplumbing threads is blunt: the best brand is the one your local plumber services and carries parts for. Rinnai, Navien, and Rheem are named most often as having real US service networks, and that is worth more than a longer warranty on paper if a heat exchanger fails in year eight.
Ask whether professional installation is required to keep the warranty valid. Nearly every manufacturer in this category conditions parts or heat exchanger coverage on licensed installation, and a few also require a permit. The Ranein listing itself recommends professional installation. Get that in writing before the plumber starts, because a 15-year heat exchanger warranty is worth nothing if the work voids it.
Venting and placement decide more purchases than buyers expect. Indoor gas units need a specific vent diameter and a location with clearance; exterior locations need an outdoor-rated model or a conversion kit, and even then freeze protection matters. Also raise the condensate question if you are considering a condensing unit, because a drain line has to go somewhere your plumber will actually run it.
Finally, ask about recirculation loops. Whole-house tankless pairs well with a demand recirculation system, and the recirculation pump can be set to trigger on the hot water return rather than on a timer, which is how you get the comfort of a tank without paying to heat water nobody uses. Confirm the unit you are buying can work with a recirculation pump before the walls are closed.
When Not to Go Tankless
Skip it if your water is very hard. Tankless units have no sediment tank, so scale from the heat exchanger is the maintenance item nobody budgets for, and in a hard-water area the descale interval can be measured in months rather than years. A conventional tank gives you a flushable anode rod and a much longer interval between service visits.
Skip it if nobody will size it correctly. An undersized unit does not fail loudly; it just runs out of hot water at 6:40 on a Tuesday, and owners describe that as the moment they regret the purchase. If you cannot commit to the sizing math in the previous section, a high-efficiency tank is the safer purchase.
Skip it if outages are routine and you have no backup. There is no stored hot water in a tankless system, period. And skip it if a 200-amp panel upgrade is not in the budget and you have no gas supply, because that is the one combination with no good answer.
Installation, Venting, and Recirculation Loops
Gas installs need a vent sized to the unit, a gas line and meter able to deliver the full BTU input, and a location with service clearance. The Rheem RTG at 160,000 BTU is the demanding case here; the APUS Q13 at 95,000 BTU is the easy one. Plan the flue before the appliance is on a truck, because re-running a vent through a finished wall is the expensive mistake.
Electric installs are plumbing plus a circuit. The Rheem RTEX-24 needs three 40-amp double-pole breakers and a 200-amp panel minimum; the Stiebel Eltron Tempra 20 Trend needs two 40-amp breakers and a 125-amp service minimum. Include a permit and panel work in any quote you compare, and remember that a listed warranty may require a licensed electrician rather than a plumber.
Recirculation is where a tankless install pays off most. A demand-controlled recirculation loop on the hot water return keeps fixtures warm without a storage tank, and it works because the tankless unit can deliver continuous hot water when the loop calls for it. The same loop, on a tank heater, is limited by how much hot water the tank holds.
Maintenance: Descaling, Filters, and Hard Water
Gas units need a filter or screen cleaned on a schedule and, in hard water, periodic descaling of the heat exchanger. Households on well water or in areas with high hardness should ask their plumber what the manufacturer recommends for descaling intervals, because there is no universal answer and every skipped interval shows up as declining flow a year later.
Electric units need the same attention to inlet filters, and more owners of the Rheem and Stiebel models report the service side. Keep the manufacturer’s technical support details somewhere other than your phone, because several brands in this roundup will troubleshoot by phone and issue a replacement credit, and that is only useful if you can reach them.
Set a calendar reminder twice a year for a visual check of the vent or exhaust path, the inlet screen, and the power or gas supply. It takes ten minutes and it is the difference between a fifteen-year heat exchanger warranty and a three-year one.
Frequently Asked Questions
What is the best tankless water heater for a whole house?
For most homes the Rheem RTEX-24 leads because it delivers 5.9 GPM from 24kW, needs no vent, and carries the deepest verified review record of any unit we covered. Large homes with three bathrooms should move up to the Rheem RTG at 7.0 GPM, and homes with no gas should stay with the electric models. The right answer is the unit whose flow rate covers your simultaneous fixture demand in your coldest month.
How big of a tankless water heater do I need for a 2000 square foot house?
A 2000 square foot house with two full bathrooms and a laundry room generally needs 5 to 6 GPM. Two showers at roughly 2.5 GPM each plus a washing machine at 1.5 GPM puts you at 6.5 GPM if everything runs at once, so size for the worst case and accept that most minutes use far less. In our roundup that range means the ThermoMate, MIZUDO, FOGATTI, or CAMPLUX models.
What do plumbers say about tankless water heaters?
Plumbers consistently point to three things: local parts and service availability matters more than brand prestige, venting and placement limit where an indoor gas unit can go, and professional installation is often required to keep a long heat exchanger warranty valid. Electric units add a fourth warning about needing a 200-amp panel or a dedicated high-amp circuit, which is the most common hidden cost in the project.
What are two disadvantages of a tankless water heater?
First, there is no stored hot water, so a power outage or a fuel outage means no hot water at all until it is resolved. Second, there is no sediment tank, so scale on the heat exchanger becomes a recurring descaling job in hard-water homes. A third practical drawback is that an undersized unit simply runs out of hot water during simultaneous use, which is a sizing error rather than a product fault.
Will I save money with a tankless water heater?
The savings come from efficiency, not from the purchase itself. Gas units in this roundup carry UEF ratings from 0.81 to 0.82 and the Rheem RTG is rated for up to 34 percent savings against a 50-gallon electric tank. Several owners report visibly lower bills after replacing a tank, but you also pay more upfront for the unit, the venting or electrical work, and periodic descaling, so model the total rather than the sticker.
Does a tankless water heater work during a power outage?
Generally no. Electric tankless units need 240V power to heat water and have no stored reserve, so they produce nothing during an outage. Gas units need 120V for the fan and control electronics, so most of the models here also shut down without power, and the Ranein in particular resets its setpoint to 129 F when power returns. If outages are routine, keep a small backup heater or plan for a hybrid system.
The Best Tankless Water Heaters for Whole House Use in 2026
The Rheem RTEX-24 is our pick for the best tankless water heaters for whole house use because 5.9 GPM, no venting, and an 894-review owner record add up to the lowest-risk decision most households can make. Homes with three or more bathrooms should step up to the Rheem RTG at 7.0 GPM, and the MIZUDO is the choice when app control and indoor or outdoor flexibility matter more than raw flow.
Whatever you choose, size for the worst minute of your day, confirm the electrical or gas requirements before you order rather than after, and get the warranty terms in writing from your installer. Those three steps prevent nearly every complaint we read about whole-house tankless units in 2026.