Small tankless water heaters are on the rise. In a lot of cases, getting a small on-demand water heater is the most energy-efficient and space-saving choice. We are going to look at the 3 smallest gas tankless water heaters (with 6.5 to 7.0 GPM max. flow rate) and the 4 smallest electric tankless water heaters (with 1.9 to 3.0 GPM max. flow rate).
These smaller tankless hot water heaters are very useful in a lot of situations, including:
- When you don’t need hot water for more than 1 shower and 1 dishwasher.
- For smaller households with 1, 2, or 3 persons.
- As a second on-demand heater (in addition to a bigger tankless water heater).
The smallest gas and electric hot water heaters have quite a few advantages over standard boiler water heaters. They produce hot water instantaneously and only when needed (no needless water heater) and take up a minimum amount of space (you don’t need to bother with big 30-gallon, 50-gallon, or even 80-gallon tanks).
According to DOE, heating water is the 2nd largest energy expense in our homes, accounting for about 18% of the utility bill. One vital advantage of the smallest on-demand water heater is also their energy efficiency. Small tankless heaters can save more on utility bills than larger on-demand heaters:
“For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24%–34% more energy efficient than conventional storage tank water heaters. They can be 8%–14% more energy efficient for homes that use a lot of hot water — around 86 gallons per day.” (US Department Of Energy on tankless water heater savings)
As you can see, getting a small tankless water heater can lower the costs of heating water by as much as 34%. Bigger heaters will reduce those costs only by up to 14%.
When checking which is the best smallest tankless water heater on the market, we have to make a choice between units powered by gas (natural gas or propane) and units powered by electricity. Here are the key differences between small gas vs electric tankless water heaters:
- Smallest gas tankless heaters can produce anywhere from 6.5 to 7.0 GPM max. flow rate. They use gas (cheaper than electricity) to produce anywhere from 10,000 BTU to 160,000 BTU of heating output. Size-wise, they can be 5 to 10 times bigger by volume than the smallest electric tankless heaters.
- Smallest electric tankless heaters are much smaller than even the smallest gas instantaneous heaters. They can produce less than 3.0 GPM max. flow rate, are powered by up to 12 kW of electricity (more expensive than gas).
Note: If you want to use a small tankless water heater for showering, make sure it has at least 2.0 GPM max. flow rate. The smallest GPM electric instantaneous heaters might have below 2.0 GPM max. flow rate and do not provide sufficient quantities of hot water for comfortable showering.
Buying even a small tankless heater for the first time usually requires some insight. That’s why we are going to cover the basic metrics (specs) you have to keep in mind when picking the right small on-demand heater for your home. After checking these specs, we are going to look at the list of the 3 best small gas tankless water heaters and at the list of the 4 best electric tankless water heaters:
9 Specs To Check When Looking At Small Tankless Hot Water Heaters
Specs we should check pertain to both what we should check with every tankless water heater as well as what to check for when selecting very small on-demand heaters.
Here is the full list of specs we need to get acquainted with if buying our 1st small tankless water heater:
- Max. Flow Rate (GPMs). This is the maximum amount of water (expressed in Gallons Per Minute or GPM) a tankless water heater can supply. The smallest gas tankless water heater has a 6.5 GPM max. flow rate while the smallest electric tankless water heater has a 1.9 GPM max. flow rate. You can check what size tankless water heater you need here.
- Heating Capacity For Gas Units (BTUs). The biggest residential gas tankless heater can produce up to 199,000 BTU of heating output. Smaller units will have a relatively high max. heating capacity (in the 120,000-160,000 BTU range) but they will have a very low minimal heating capacity (in the 10,300 to 15,000 BTU range).
- Max. Power Input For Electric Units (kWs). Electric units ‘burn’ electricity (measured in kilowatts) instead of gas. The biggest electric tankless water heaters can have a very high 30+ kW electric input. The smallest electric on-demand hot water heaters will have below 15 kW electric input (even as low as 8 kW). You can check how much electricity do electric tankless water heater use here.
- Minimal Activation Rate. Both small gas and electric tankless water heaters should have below 0.8 GPM min. activation rate. The smallest gas units will have a 0.5 GPM or lower activation rate while electric tankless units can have as low as 0.3 GPM min. activation rate.
- Uniform Energy Factor (UEF) And Running Cost For Gas Units. Electric units are almost 100% efficient; gas units, in comparison, can have below 75% energy efficiency. The most energy-efficient small gas tankless water heaters will have above 80% uniform energy factor. Higher UEF units will have a lower specific EnergyGuide label running cost (around $200/year for the smallest units).
- Amp Breaker Size For Electric Units. Electric on-demand heaters run on 240V and can have an amp draw exceeding 100 amps. The smallest electric tankless heater will have an up to 50A amp draw and will require only two 30 amp breakers and AWG 8 or AWG 6 wires. You can check how many amps do these electric tankless water heaters draw here.
- Dimensions Of Tankless Water Heaters. Gas units can have a 20+ inch width, 35+ inch height, and 12+ inch depth. Dimension-wise, the smallest gas tankless heaters will have below 15-inch width, below 26-inch height, and below 10-inch depth. Bigger electric heaters can also take up quite a bit of space; that’s why, when selecting small electric tankless units, make sure that they have below 20-inch width and height, and below 5-inch depth.
- Volume Of Tankless Water Heaters. Standard storage tank water heaters will often have 20,000+ cubic inch volume. Big gas tankless water heaters can have 10,000+ cubic inch volume; for volume-small units, go for below 5,000 cubic inch gas units. Small electric units can have a below 1,000 cubic inch volume (5 times or even 10 times lower than gas units).
- Reputable Brands. Always go for the best tankless water heater brands. Tankless heaters are not something any no-name company can make. The best brands for small tankless water heaters are Rinnai, Noritz, and Rheem for gas units, and Stiebel Eltron, Ecosmart, and Rheem for electric units.
With these key specs in mind, let’s first have a look at the smallest gas-powered on-demand heaters, followed by the smallest electric-powered on-demand heaters:
Smallest Gas Tankless Water Heaters
1. Smallest Gas Tankless Heater With Superb Specs: Rinnai V65iN
|Max. Flow Rate:||6.5 GPM|
|Heating Capacity:||10,300 – 150,000 BTU|
|Min. Activation Rate:||0.4 GPM|
|Dimensions (W×H×D):||14×23×9 Inches|
|Size (Volume):||2898 Cubic Inches|
Rinnai is the world’s best gas tankless water heater producer. They offer a wide array of on-demand heaters spanning from the smallest to the biggest 199,000 BTU gas tankless heaters. Their smallest and best small tankless water heater on the market is the Rinnai V65iN.
It has the lowest max. flow rate of 6.5 GPM. This is enough to use up to 5 faucets simultaneously. Practically, you can run anything from a hot water faucet in the kitchen to 1 or even 2 small showers simultaneously.
That’s because it has quite a range as far as heating capacity is concerned. It has the lowest heating capacity of only 10,300 BTU (at min. activation rate of 0.4 GPM). When you need to use a shower and an additional faucet, however, it can switch to a high heating capacity with up to 150,000 BTU of heating output.
Despite being so small (suitcase-small, even), it can achieve a high 82% energy efficiency (UEF = 0.82). This lowers its running cost to below $200 per year ($199, to be exact). With average use, it will use 183 therms of natural gas; the $199/year running cost derives from its EnergyGuide label with the presumed natural gas cost of $1.09/therm.
Dimensions-wise and volume-wise, it is one of the smallest gas tankless water heaters as well. It has 14-inch width, 23-inch height, and 9-inch thickness (depth). The total volume of the Rinnai V65iN is 2898 cubic inches; far below the 20,000 cubic inches that a bigger storage tank water heater can have.
Of course, even Rinnai tankless heaters are not without shortcomings. Due to its mini size, it is a non-condensing unit. It’s just very hard to engineer condensing in such a small unit without increasing its volume or limiting its great specs. If it were a condensing unit, the UEF factor could exceed 0.85.
Despite being a Rinnai unit, it has quite a fair price. With a below $800 price tag, it is one of the best price-performing gas tankless water heaters on the market.
All in all, the Rinnai V65iN is the go-to choice as the smallest gas tankless water heater. It is perfect for lower hot water needs, has the lowest max. flow rate (6.5 GPM) and it is – dimensions-wise – the size of a bigger suitcase:
2. Very Small Energy Efficient Gas Tankless Heater: Noritz NRC66DVNG
|Max. Flow Rate:||6.6 GPM|
|Heating Capacity:||15,000 – 120,000 BTU|
|Min. Activation Rate:||0.5 GPM|
|Dimensions (W×H×D):||13.8×23.6×6.7 Inches|
|Size (Volume):||2182 Cubic Inches|
Noritz is another reputable gas tankless water heater producer. They are specialized in condensing low-NOx units that have very high energy efficiency (high natural gas efficiency). The smallest Noritz gas tankless heater is the Noritz NRC66DVNG that’s even smaller than the Rinnai unit dimensions-wise and is the most energy-efficient small gas tankless water heater on the market.
Noritz NRC66DVNG can use its 15,000 BTU to 120,000 BTU heating element to produce the max. flow rate of 6.6 GPM. This is comparable with the small Rinnai unit producing up to 6.5 GPM.
Where Noritz has an advantage even over the Rinnai unit is the condensation and therefore energy efficiency. Noritz NRC66DVNG is the smallest condensing tankless gas water heater. This increase it’s energy efficiency to 89% (UEF = 0.89), making it the most energy-efficient small tankless gas-powered water heater.
Due to such a high energy efficiency and small flow rate, it only costs $136/year to operate, according to the EnergyGuide label.
It does, however, has a bit higher min. activation rate. This natural gas heater turns on only at 0.5 GPM flow rate (compared to the lower 0.4 GPM flow rate Rinnai and Rheem units have).
Dimensions-wise, it is the smallest gas tankless water heater thanks to how thin it is. Even the very small units will have about 10-inch thickness. Comparatively, the Noritz NRC66DVNG is only 6.7 inches in thickness. It has the lowest total volume of 2182 cubic inches as a result.
Obviously, high-energy efficiency units are more expensive than units without condensation. Noritz NRC66DVNG does cost more than $1000 but it does have the lowest running costs.
All in all, Noritz NRC66DVNG is the smallest (volumetric and dimensions-wise) tankless water heater. It is one of the best condensing gas tankless water heaters with 89% efficiency:
3. Good Small On Demand Gas Water Heater: Rheem RTG-70DVLN-1
|Max. Flow Rate:||7.0 GPM|
|Heating Capacity:||15,000 – 160,000 BTU|
|Running Cost:||$212/Year (Est.)|
|Min. Activation Rate:||0.4 GPM|
|Dimensions (W×H×D):||13.9×25.6×9.9 Inches|
|Size (Volume):||3523 Cubic Inches|
Rheem is also an established brand in HVAC. They make superb gas and electric on-demand heaters. Their smallest gas unit is the Rheem RTG-70DVLN-1 which features a remote electronic thermostat that can pre-heat water to 85˚F – 140˚F seconds before you need to take a shower.
Rheem RTG-70DVLN-1 has the max. flow rate of 7.0 GPM but it can reduce the heating output to as low as 15,000 BTU. That means that you can use it for everything from using 1 faucet to wash vegetables to running 1 big or 2 small showers instantaneously.
It has the same energy efficiency as the Rinnai unit (82% with 0.82 UEF factor) and a yearly running rate of $212. That’s $13/year higher than the Rinnai unit since it is a bit bigger unit (7.0 GPM vs 6.5 GPM).
Gladly, it has the lowest 0.4 GPM minimum activation rate.
Dimensions-wise, it is very small 3523 cubic inches of volume, but both Rinnai and Noritz units do have a volume lower than 3000 cubic inches. That’s because it is a bit higher (25.6-inch height) and a bit thicker (9.9-inch depth).
It does not have as high a price as a high-efficiency condensing Noritz unit. The price tag of Rheem RTG-70DVLN-1 is about $800 vs. $1100 for the Noritz unit.
In short, Rheem RTG-70DVLN-1 is not the smallest unit but it is one of the best small instantaneous water heaters with a remote pre-heat function, available at an affordable price:
With the best small gas-powered instantaneous water heaters covered, let’s have a look at the smallest electric-powered tankless water heaters as well:
Smallest Electric Tankless Heaters On The Market
1. Best Small Electric Tankless Water Heater: Stiebel Eltron Tempra 12 Plus
|Max. Power Input:||12 kW|
|Flow Rate:||3.0 GPM|
|Min. Activation Rate:||0.37 GPM|
|Dimensions (W×H×D):||4.6 × 16.6 × 14.5 Inches|
|Size (Volume):||1107 Cubic Inches|
|Amp Draw:||Up To 50 Amps|
German company Stiebel Eltron is to electric tankless water heaters what Japanese company Rinnai is to gas units. In short, Stiebel Eltron is the world’s best producer of electric on-demand heaters. They have a big portfolio of reliable units, and their Stiebel Eltron Tempra 12 Plus model is the best small electric tankless water heater on the market.
Stiebel Eltron Tempra 12 Plus has the max. power input of 12 kW. Mind you, this is not the lowest power input (the smallest electric tankless heaters can have as low as 8 kW input). However, it is important to have an above 3.0 GPM flow rate if you want to use a small electric on-demand water heater for showering (requires 2.0 GPM), and with 12 kW Tempra 12 Plus can achieve that.
It can heat up water temperatures anywhere from 68°F to 140°F. Here are the specific water temperature increases and corresponding flow rates (GPMs):
- It can achieve 1.50 GPM for a very steep 54°F water temperature increase.
- It can achieve 2.25 GPM for a steep 36°F water temperature increase.
- It can achieve 3.00 GPM for a lower 27°F water temperature increase.
The activation rate here needs to be very low and it is: Stiebel Eltron Tempra 12 Plus has a 0.37 GPM min. activation rate. That’s lower than even the smallest gas tankless water heaters.
Dimensions-wise and volume-wise, the Stiebel Eltron Tempra 12 Plus is not the smallest as well; and that is by design. Namely, it is quite wide (14.5-inch width) and a bit thicker than other small electric tankless heaters (4.6-inch thickness). On top of that, it weighs 19 lbs vs below 10 lbs many of the smallest tankless heaters have.
The reason for a big bigger volume (above 1000 cubic inches) and higher weight is reliability. Stiebel Eltron is synonymous with reliability. To ensure that the electric unit is durable, Stiebel Eltron uses higher-quality materials that are heavier and advanced engineering; that’s why we see bigger size specs.
With electric units, the wiring is also important. Due to a 12 kW power draw at 240V, the Stiebel Eltron Tempra 12 Plus has a 50 amp draw. That means you will need two 30 amp breakers (for a total of 60A) and you will have to use AWG 8 (50A ampacity) or AWG 6 (65A ampacity) wires.
Obviously, Stiebel Eltron Tempra 12 Plus is not the cheapest small electric on-demand water heater on the market. Due to the reliability and good brand reputation Stiebel Eltron enjoys, the price of the Tempra 12 Plus is about $450.
All in all, the Stiebel Eltron Tempra 12 Plus is the go-to best small electric tankless water heater for showering. It is a big bigger than the smallest units but none of those can match Stiebel Eltron in terms of reliability and lifespan:
2. Smallest Electric Tankless Water Heater: Ecosmart ECO 8
|Max. Power Input:||8 kW|
|Flow Rate:||1.9 GPM|
|Min. Activation Rate:||0.3 GPM|
|Dimensions (W×H×D):||3.8 × 11.5 × 8 Inches|
|Size (Volume):||350 Cubic Inches|
|Amp Draw:||Up To 33 Amps|
Ecosmart is a niche brand, specializing in producing both big and small tankless electric water heaters. Their Ecosmart ECO 8 unit is the absolute smallest electric on-demand hot water heater on the market. Let’s look at these record small specs:
The max. flow rate is 1.9 GPM. This is the minimum max. flow rate of any electric or gas tankless water heater. This is both a pro and a con; the Ecosmart ECO 8 itself can be extra small and requires only 8 kW input. However, if you want to use a small tankless electric water heater for showering, the Ecosmart ECO 8 can actually be too small (you would need about 2.0 GPM for comfortable showering).
If you check the dimensions and total volume, you can see this is a truly mini electric tankless water heater. It is only 11.5 inches high, 8 inches wide, and 3.8 inches thick, for a total volume of merely 350 cubic inches. In short, it is smaller than your average space heater, which is just outstanding for a 1.9 GPM water heater with an 8 kW power input.
The benefit here is that you won’t have to use big or several amp breakers or thick wires for installation. The Ecosmart ECO 8 has a max. amp draw of only 33 amps on a 240V circuit. That means you will require fewer amp breakers (a 50A breaker is more than enough) and AWG 10 wire will be sufficient for wiring.
Obviously, Ecosmart ECO cannot compare with Stiebel Eltron as far as reliability is concerned (no brand is as reliable as Stiebel Eltron). However, Ecosmart ECO costs about 50% as much as Tempra Plus 12, with a price tag of around $250.
All in all, if you are looking for the absolute smallest tankless water heater, the Ecosmart ECO 8 is just that. It has the smallest dimensions, lowest volume, lowest max. flow rate, and requires the least amount of electric circuit upgrades to install:
3. Smallest Rheem Electric Tankless Water Heater: Rheem RTEX-08
|Max. Power Input:||8 kW|
|Flow Rate:||1.95 GPM|
|Min. Activation Rate:||/|
|Dimensions (W×H×D):||3.6 × 12.6 × 8.3 Inches|
|Size (Volume):||375 Cubic Inches|
|Amp Draw:||Up To 33 Amps|
Rheem is one of the few companies that make both super gas as well as electric tankless water heaters. Their Rheem RTEX-08 is the smallest Rheem electric tankless water heater and it’s also one of the super small units dimension-wise that is quite reliable.
Similar to Ecosmart ECO 8, the Rheem RTEX-08 is powered by an 8 kW electric input. Due to high energy efficiency, such 8 kilowatts can produce max. flow rate of 1.95 GPM. That is almost enough for showering (2.0 GPM requirement). It is best used, however, for simultaneously using multiple faucets, running a dishwasher, and so on.
Volume-wise, it is almost as small as Ecosmart (375 cubic inches vs 350 cubic inches). It is, however, much thinner with a 3.6-inch depth.
Unlike Ecosmart, the Rheem units do have a long track record for reliability. Rheem also has a good record for producing price-performance electric tankless heaters. With a below $250 price tag, this is certainly the case for Rheem RTEX-08 as well.
8 kW 240V power input also means that you won’t have to completely upgrade the electric circuit. 50A breaker will be more than enough and you can even use AWG 10 wiring.
All in all, Rheem RTEX-08 is one of the best smallest electric tankless water heaters on the market. Dimensions-wise, it is one of the thinnest and space-saving units that can achieve max. flow rate of almost 2.0 GPM:
4. Cheap Small Electric Tankless Water Heater: Thermomate ET110
|Max. Power Input:||11 kW|
|Flow Rate:||2.15 GPM|
|Min. Activation Rate:||/|
|Dimensions (W×H×D):||3.1 × 14.8 × 11.8 Inches|
|Size (Volume):||541 Cubic Inches|
|Amp Draw:||Up To 46 Amps|
Thermomate is one of the few no-name brands that can make a good electric tankless water heater. It doesn’t have the brand recognition Eltron Stiebel or Rheem have but, specs-wise, it has created a very good and quite popular small Thermomate ET110 that can be used for showering.
That’s because of the max. flow rate of Thermomate ET110 is 2.15 GPM (at 35°F water temperature rise). That is enough for running a shower if you have a fairly high inlet water temperature (US southern states like Florida, Texas, California, etc.).
To achieve that flow rate, the Thermomate ET110 uses an 11 kW electric input. On a 240V circuit, that means you will have to prepare your circuit for a 46 amp draw. That means one 50A breaker or two 30A breakers with AWG 8, AWG 6, or AWG 6/2 wires.
Dimensions-wise, the Thermomate ET110 has a record-low thickness. It is only 3.1 inches thick, resulting in a minimal 541 cubic inches of volume for the whole unit.
These specs are quite impressive; the reliability of Thermomate, however, is less so. Most lesser-known brands like Thermomate will not have a decades-long track record that proves that tankless water heaters are durable and reliable.
The price of the Thermomate ET110 is about the same as the price of Ecosmart and Rheem units (in the $200 – $250 range).
In short, Thermomate ET110 is definitely one of the smallest electric tankless water heaters. It does have great specs but the reliability is sadly questionable since this is not an established well-known brand:
This has been an overview of the smallest gas and electric tankless water heaters. When choosing a small on-demand tankless hot water heater, keep in mind the 9 specs we listed above. Hopefully, with suggestions of the small gas and small electric tankless water heaters from the best brands such as Rinnai, Eltron Stiebel, Rheem, and Noritz, you will now be able to make a bit more informed decision on which is the best small tankless water heater for your home.