Top Tankless Water Heater Brands for Reliable Hot Water

Choosing the right tankless water heater is crucial for ensuring a consistent supply of hot water while minimizing energy costs. With various options available, it’s essential to find a model that fits your household’s specific needs.

Tankless Water Heater Comparison

Product	Best for	Flow Rate (GPM)	Power (kW)	Dimensions	Weight	Price
Rheem RTEX-24 Electric Tankless Water Heater	Best Overall	5.9	24	—	—	Check price
Rheem 18kW Electric Tankless Water Heater	Best Mid-Range	4.4	18	—	—	Check price
Rheem 8kW Multi Fixture Tankless Water Heater	Best for Small Demand	1.95	8	—	—	Check price
xwdzswgs 3000W Electric Tankless Water Heater	Best Compact Unit	0.3 – 0.5	3	—	—	Check price
6699 Tankless Water Heater Flushing Kit	Best Maintenance Kit	—	—	6.3 x 6.3 x 8.7 inches	—	Check price

Top Picks for Tankless Water Heaters

1

Best Overall

Rheem RTEX-24 Electric Tankless Water Heater

Best for: Homes needing up to 5.9 GPM for multiple fixtures

The Rheem RTEX-24 delivers up to 5.9 GPM with 24 kW power, suitable for various household applications. Its digital thermostatic controls allow precise temperature settings from 80°F to 140°F. Requires a 240V supply with three 40-amp breakers, fitting homes with a 200-amp panel. Ideal for users who want energy savings by heating water only on demand.

• Flow Rate (GPM)5.9
• Power (kW)24
• Wiring Requirements240V, three 40-amp breakers, #8 AWG copper conductors
• Temperature Range80°F – 140°F

Pros

• High flow rate supports multiple fixtures
• Precise digital temperature control
• Energy efficient by heating water on demand

Cons

• Requires significant electrical capacity and professional installation
• Not suitable for homes with lower electrical service panels

Skip it if: Skip if your home electrical panel cannot support three 40-amp breakers or you need less than 5.9 GPM.

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2

Best Mid-Range

Rheem 18kW Electric Tankless Water Heater

Best for: Homes needing up to 4.4 GPM with moderate electrical capacity

This Rheem 18kW model offers up to 4.4 GPM and advanced self-modulation technology to match hot water output to demand. It features durable copper immersion heating elements that are field serviceable. The external digital thermostat with LED display allows precise control. Suitable for households with a 240V supply and simpler wiring needs compared to the RTEX-24.

• Flow Rate (GPM)4.4
• Power (kW)18
• InstallationBottom 3/4 inch NPT water connections
• Temperature ControlExternal digital thermostat with LED

Pros

• Self-modulating power adjusts to demand
• Copper heating elements are durable and serviceable
• Simple installation with bottom 3/4 inch NPT water connections

Cons

• Lower maximum flow rate than larger models
• Requires 240V power supply

Skip it if: Skip if you need more than 4.4 GPM or have a lower voltage supply.

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3

Best for Small Demand

Rheem 8kW Multi Fixture Tankless Water Heater

Best for: Small households or single fixtures needing up to 1.95 GPM

The Rheem 8kW model supports up to 1.95 GPM, ideal for a single fixture or small household use. It requires only one 40-amp breaker and a minimum 100-amp panel, making it easier to install in homes with less electrical capacity. Digital thermostatic controls allow temperature adjustment between 80°F and 140°F. Energy efficient by heating water only when needed.

• Flow Rate (GPM)1.95
• Power (kW)8
• Wiring Requirements240V, one 40-amp breaker
• Temperature Range80°F – 140°F

Pros

• Compact size with low electrical requirements
• Digital temperature control in 1-degree increments
• Suitable for multiple small fixture applications

Cons

• Low flow rate limits simultaneous use
• Not for whole-house applications

Skip it if: Skip if you need more than 1.95 GPM or multiple large fixtures.

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4

Best Compact Unit

xwdzswgs 3000W Electric Tankless Water Heater

Best for: Under-sink or single-point use with low flow demand

This 3,000W tankless heater provides instant hot water with a compact, wall-mounted design that saves space. It can raise water temperature significantly at low flow rates (0.3 to 0.5 GPM). The unit includes multiple safety protections such as leakage and over-temperature shutdown and meets ETL standards. Best for small applications like kitchen sinks or bathrooms with low hot water demand.

• Power (kW)3
• Flow Rate (GPM)0.3 – 0.5
• Safety FeaturesLeakage protection, dry-burning protection, automatic power-
• InstallationVertical mounting only

Pros

• Compact and lightweight design
• Multiple safety features including dry-burning protection
• Easy installation with standard 1/2 inch NPT connections

Cons

• Very low flow rate limits use to single fixtures
• Vertical installation only to avoid heating element damage

Skip it if: Skip if you need more than 0.5 GPM or whole-house heating.

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5

Best Maintenance Kit

6699 Tankless Water Heater Flushing Kit

Best for: Keeping tankless water heaters clean and efficient

This flushing kit includes a 1/4 HP submersible pump, hoses, and a 3-gallon bucket with a lid opener to maintain and extend the life of tankless water heaters. The pump delivers up to 1500 GPH and can handle fluid temperatures up to 95°F. The ergonomic bucket lid opener makes flushing easier and safer. Essential for regular maintenance to prevent scale buildup and preserve performance.

• Pump Power1/4 HP
• Pump Flow Rate1500 GPH
• Pump Max Fluid Temperature95°F
• Pump Max Head16.5 FT

Pros

• Complete kit for tankless water heater flushing
• Pump with thermal overload protection
• Ergonomic lid opener for easy access

Cons

• Not a water heater itself
• Requires some setup and effort for flushing

Skip it if: Skip if you do not perform regular maintenance on your tankless water heater.

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How to Choose the Right Tankless Water Heater

Choosing a tankless water heater starts with knowing your household’s hot water needs. The key factor is the flow rate, measured in gallons per minute (GPM). This tells you how much hot water the unit can deliver at once. Pick a model that matches or slightly exceeds your peak demand to avoid running out of hot water during busy times.

Next, check the power requirements. Electric tankless heaters like the Rheem RTEX-24 usually need a 240-volt circuit and can draw up to 24 kW. Make sure your home’s electrical panel has the capacity for the heater you want. Oversized breakers or inadequate wiring can cause trips or unsafe conditions.

Size and installation space also matter. Tankless units are compact, but you still need clearance for airflow and maintenance. Measure the wall or area where you plan to mount the heater and compare it to the unit’s dimensions. Some models fit tight spaces better, which is crucial in small utility rooms or apartments.

Energy efficiency ratings help you choose a model that saves on utility bills. Look for units with high energy factor (EF) or uniform energy factor (UEF) ratings. Higher numbers mean less energy wasted heating water. This is especially important if you plan to use the heater frequently or want lower monthly costs.

Sizing and Heat Output for Tankless Water Heaters

Sizing a tankless water heater means matching its output to your household’s peak hot water demand. Start by listing all fixtures you expect to use simultaneously—showers, faucets, appliances—and note their typical flow rates.

Add the flow rates to find the total gallons per minute (GPM) needed. For example, a shower uses about 2.5 GPM, a bathroom sink 1 GPM, and a dishwasher 1.5 GPM. If you plan to run a shower and dishwasher at the same time, your heater needs to supply at least 4 GPM continuously.

The inlet water temperature affects the heater’s performance. Colder incoming water requires more energy to heat to your desired temperature. In northern states, inlet water can be as low as 40°F, while southern states may see 70°F or higher. Tankless heaters list their maximum flow rate based on a specific temperature rise, usually 70°F. If your inlet water is colder, the actual flow rate will be lower.

1. Calculate Peak Demand
   List all fixtures used at the same time and note their flow rates.
2. Add Flow Rates
   Sum the GPM values to find total hot water needed simultaneously.
3. Check Inlet Temperature
   Estimate your cold water temperature to understand the required temperature rise.
4. Match Heater Capacity
   Choose a heater with a GPM rating that meets or exceeds your calculated demand at your inlet temperature.

For detailed models and sizing help, see our guide on best propane tankless water heater and other specialized units.

Running Costs of Tankless Water Heaters

Tankless water heater safety features protect users and equipment from electrical and thermal hazards. Look for models certified by UL (Underwriters Laboratories) or ETL (Intertek), which verify compliance with rigorous safety standards.

Essential safety features include overheat protection, which shuts off the heater if water temperature exceeds safe limits, and automatic shut-off that activates during faults or power surges. These prevent damage and reduce fire risk.

Proper installation is critical for safety and performance. Licensed plumbers or electricians should handle wiring and plumbing connections, ensuring the unit meets local codes and manufacturer instructions. Incorrect installation can cause leaks, electrical hazards, or void warranties.

Safety and Certification for Tankless Water Heaters

Tankless water heater safety features protect users and equipment from electrical and thermal hazards. Look for models with UL or ETL certification, which means they meet strict safety and performance standards set by independent labs. These certifications confirm the unit has passed tests for electrical safety, fire risk, and durability.

Overheat protection is essential. It shuts the heater off if the water temperature rises above safe levels, preventing damage and burns. Automatic shut-off features also cut power if the unit detects a fault or if water flow stops unexpectedly.

Proper installation is critical. A licensed plumber or electrician should handle setup to ensure wiring, grounding, and water connections meet local codes. Incorrect installation increases risks of fire, leaks, or electric shock.

Maintenance Tips for Tankless Water Heaters

How to maintain a tankless water heater starts with regular descaling to remove mineral buildup. Hard water causes scale that reduces heat transfer and flow, lowering efficiency and lifespan.

1. Turn off power and water supply
   Switch off the unit at the breaker and close the water valves to prevent leaks.
2. Attach the flushing kit
   Connect the flushing kit hoses to the service ports on the heater as per the kit instructions.
3. Circulate descaling solution
   Run a vinegar or commercial descaling solution through the heater using a pump for 45 to 60 minutes.
4. Flush with clean water
   After descaling, flush the system with fresh water to remove any residue.
5. Restore water and power
   Close the service ports, open the water valves, and turn the power back on.

Common signs of mineral buildup include fluctuating water temperature, reduced flow rate, and unusual noises from the unit. Flushing at least once a year prevents these issues and keeps the heater running efficiently.

Recommended flushing kit

6699 Tankless Water Heater Flushing Kit

The 6699 Tankless Water Heater Flushing Kit fits most models and simplifies the descaling process with clear instructions and reliable connections.

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Frequently Asked Questions