14 kW or 27 kW Tankless Water Heaters? Compared by Specs
As an Amazon Associate we earn from qualifying purchases. Links on this page are affiliate links.
Choosing between a 14 kW vs 27 kW tankless water heater depends on your household’s hot water demand. Both units are electric, wall-mounted, and ETL certified for safety. They share cast aluminum heating chambers and self-modulating technology for efficiency. The main difference is power output. The 14 kW model suits low-flow applications, while the 27 kW unit supports multiple fixtures. Your electrical panel capacity and desired flow rate determine which size fits your home.
Key differences
| Aspect | Thermomate 14 kW Cast Aluminum Tankless Water Heater | Thermomate 27kW 6.6 GPM Electric Tankless Water Heater |
|---|---|---|
| Wattage | 14 kW | 27 kW |
| Max Flow Rate | 3.4 GPM | 6.6 GPM |
| Temperature Range | 86 to 131°F | 80 to 140°F |
| Electrical Requirement | 1 x 60A breaker | 3 x 40A breakers |
| Water Connections | 1/2" NPT | 3/4" NPT |
| Dimensions | 15.4 x 12.8 x 12.8 in | 17.09 x 13.15 x 3.15 in |
Which one should you choose?
Choose Thermomate 14 kW Cast Aluminum Tankless Water Heater if
- You need hot water for a single bathroom or small sink.
- Your electrical panel has limited capacity and cannot support three separate circuits.
- You prefer a wider unit with a deeper profile for standard 1/2-inch plumbing.
Choose Thermomate 27kW 6.6 GPM Electric Tankless Water Heater if
- You plan to run two showers and a sink simultaneously.
- Your main panel has at least 150 Amps of total capacity.
- You want a wider temperature range up to 140°F for dishwasher use.
Verdict: The 14 kW model is sufficient for point-of-use or single-bathroom setups with limited electrical space. The 27 kW unit is necessary for whole-house or multi-bathroom homes requiring high flow rates. Select the 27 kW version only if your electrical infrastructure supports the required three-breaker setup.
14 kW vs 27 kW Spec Comparison
Wattage Output
The ThermoMate 14 kW model delivers 14 kilowatts of heating power, making it suitable for point-of-use applications or single fixtures. In contrast, the ThermoMate 27 kW unit provides 27 kilowatts, offering nearly double the thermal energy. This higher wattage allows the larger unit to handle more simultaneous demand. You will notice a significant difference in heating capacity between these two options. The 27 kW model is designed for whole-house needs or multiple bathrooms, while the 14 kW unit is better for smaller setups. Your choice depends entirely on how much hot water you need at once.
Flow Rate Capacity
Flow rate determines how much hot water you can get from a faucet or shower. The ThermoMate 14 kW unit supports up to 3.4 GPM, which is sufficient for one shower and a small sink. The ThermoMate 27 kW unit supports up to 6.6 GPM, allowing for two showers and a sink to run simultaneously. If you have a large family or multiple bathrooms, the higher flow rate of the 27 kW model is essential. The 14 kW unit may struggle to maintain temperature if multiple fixtures are used. This spec is critical for daily comfort and convenience in your home.
Electrical Requirements
Both units operate on 240 V power, but their electrical demands differ greatly. The ThermoMate 14 kW requires a double-pole 60 Amp breaker and 6 AWG wire. The ThermoMate 27 kW needs three separate 40 Amp double-pole breakers and three sets of 8 AWG copper wires. You must ensure your main panel has at least 150 Amps of capacity for the 27 kW model. The 14 kW unit is easier to install in homes with standard electrical panels. The 27 kW model requires a more complex electrical setup, which may involve upgrading your home's service.
Water Connections
The physical connection to your plumbing system varies between these two models. The ThermoMate 14 kW uses 1/2 inch NPT male ports, which are standard for many residential point-of-use installations. The ThermoMate 27 kW uses 3/4 inch NPT connections, which are necessary to support its higher flow rate. If your existing plumbing uses 1/2 inch pipes, the 14 kW unit will fit directly without adapters. The 27 kW unit may require plumbing modifications to accommodate the larger 3/4 inch connections. This detail affects the ease and cost of installation for your specific setup.
Temperature Control Range
Both units offer adjustable temperature settings, but the ranges differ slightly. The ThermoMate 14 kW allows you to set temperatures from 86 to 131°F in 1-degree increments. The ThermoMate 27 kW offers a range from 80°F to 140°F. The 27 kW unit provides a wider span, allowing for lower temperatures for gentle washing or higher temperatures for sanitizing. The 14 kW unit’s finer 1-degree increments give you precise control within its narrower range. Both use electronic controls for stability. Your preference for specific water temperatures will dictate which range suits your needs better.
Which unit fits your hot water needs?
Single bathroom or point-of-use sink
The 14 kW model supports up to 3.4 GPM, which is ideal for one shower or sink. It requires only one 60 Amp breaker and 6 AWG wire. The compact 15.4-inch height fits tight spaces. You get precise 1-degree temperature adjustments from 86 to 131°F. This lower power draw suits homes with limited electrical capacity.
Whole-house or multi-fixture supply
The 27 kW unit delivers 6.6 GPM, handling three to four fixtures simultaneously. It uses 3/4-inch NPT connections for higher flow. You need three 40 Amp breakers and 8 AWG wires. The temperature range extends to 140°F. This higher output ensures steady hot water for larger households or commercial use without pressure drops.
Limited electrical panel capacity
You only need one double-pole 60 Amp breaker for the 14 kW heater. The 27 kW model requires three separate breakers and a 150 Amp main panel. If your electrical system cannot support the higher load, the 14 kW unit is the safer, simpler choice. It draws less current while still providing endless hot water for low-flow applications.
Quick picks
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | Thermomate 14 kW Cast Aluminum Tankless Water Heater | Single bathroom or point-of-use applications | Check price of Thermomate 14 kW Cast Aluminum Tankless Water Heater on Amazon |
| 2 | Thermomate 27kW 6.6 GPM Electric Tankless Water Heater | Multi-fixture homes with 150-amp panels | Check price of Thermomate 27kW 6.6 GPM Electric Tankless Water Heater on Amazon |
The products compared
Thermomate 14 kW Cast Aluminum Tankless Water Heater
Best for: Single bathroom or point-of-use applications
- Wattage
- 14 kW (what this guide is about)
- Fuel Type
- Electric
- Flow Rate
- 3.4 GPM
- Installation Location
- Indoor
- Voltage
- 240V
- Temperature Control
- 86°F–131°F
View on Amazon: Thermomate 14 kW Cast Aluminum Tankless Water Heater Affiliate link
This 14 kW electric unit delivers up to 3.4 GPM of hot water. It features a cast aluminum heating chamber for durability and self-modulating technology for efficiency. The unit measures 15.4 x 12.8 x 12.8 inches and weighs 13.7 pounds. It requires a 60-amp double-pole breaker. This model suits point-of-use applications or small bathrooms where space is tight and flow needs are moderate.
Pros
- 14 kW power output supports up to 2 faucets or 1 shower
- Cast aluminum heating chamber resists scale and corrosion
- Electronic control adjusts temperature in 1°F increments from 86 to 131°F
- ETL Listed to UL-499 and CAN/CSA-C22.2 No. 64
Cons
- 14 kW is half the power of the 27 kW alternative on this list
- Requires a dedicated 60-amp double-pole breaker for installation
- Maximum flow rate of 3.4 GPM may limit simultaneous use
Good fit if
- You need a compact unit for a single bathroom or small sink
- You have the electrical capacity for a 60-amp breaker
- You want precise temperature control in 1-degree increments
Skip if
- You need to run multiple showers simultaneously
- You cannot install a 60-amp double-pole breaker
- You require higher flow rates than 3.4 GPM
Verdict: Thermomate 14kW Electric Tankless Heater fits single-bathroom setups or point-of-use needs where space is limited. It offers precise control and efficient heating but lacks the power for high-demand multi-fixture use.
Thermomate 27kW 6.6 GPM Electric Tankless Water Heater
Best for: Multi-fixture homes with 150-amp panels
- Wattage
- 27 kW (what this guide is about)
- Fuel Type
- Electric
- Flow Rate
- Up to 6.6 GPM
- Installation Location
- Indoor
- Voltage
- 240 V
- Temperature Control
- 80°F to 140°F
View on Amazon: Thermomate 27kW 6.6 GPM Electric Tankless Water Heater Affiliate link
This ThermoMate 27kW electric unit delivers up to 6.6 GPM of hot water. It requires a 150-amp main panel and three 40-amp breakers. The cast aluminum heating block resists scale. Smart modulation keeps output stable between 80°F and 140°F. Its compact 17.1-inch height fits tight spaces. It suits multi-fixture homes with strong electrical service.
Pros
- 27 kW power for up to 6.6 GPM flow
- Cast aluminum heating element resists corrosion
- ETL certified for safety compliance
- Smart modulation maintains temperature stability
Cons
- Requires three separate 40-amp double-pole breakers
- Needs 8 AWG copper wiring for installation
- High electrical demand limits use in older homes
Good fit if
- You have a 150-amp electrical panel
- You need hot water for multiple fixtures
- You want a compact wall-mounted unit
Skip if
- You have an electrical panel under 150 amps
- You cannot install three 40-amp breakers
- You need a lower wattage unit
Verdict: ThermoMate 27kW Electric Tankless Heater fits homes with robust electrical infrastructure needing high flow. It delivers consistent heat for busy households. Buyers with limited panel space should look elsewhere.
Specifications side by side
| Spec | Thermomate 14 kW Cast Aluminum Tankless Water Heater | Thermomate 27kW 6.6 GPM Electric Tankless Water Heater |
|---|---|---|
| Fuel Type | Electric | Electric |
| Flow Rate | 3.4 GPM | Up to 6.6 GPM |
| Wattage | 14 kW | 27 kW |
| Installation Location | Indoor | Indoor |
| Voltage | 240V | 240 V |
| Temperature Control | 86°F–131°F | 80°F to 140°F |
| Certification | ETL, UL-499, CAN/CSA-C22.2 No. 64 | ETL Listed |
| Dimensions | 15.4 x 12.8 x 12.8 in | 17.09 x 13.15 x 3.15 inches |
| Weight | 13.7 pounds | 19 pounds |
| Color | Gray | Gray |
| Model | ET140 | EH270 |
Frequently asked questions
Can a 14 kW unit handle a full bathroom?
Yes, but only for single-fixture use. The Thermomate 14 kW model supports up to 3.4 GPM, making it ideal for one shower or sink. It is not suitable for running multiple fixtures simultaneously. This unit fits single-bathroom setups or point-of-use applications where space is limited.
What electrical panel size do I need for the 27 kW heater?
You need a robust electrical infrastructure, specifically a 150-amp panel. The 27 kW unit draws significant power to deliver high flow rates. It is designed for homes that can support this higher demand. Buyers with limited panel space should look elsewhere for a lower-wattage option.
How much bigger is the 27 kW unit than the 14 kW?
The 27 kW model is slightly larger in height and width. It measures 17.1 inches tall and 13.2 inches wide, compared to the 14 kW unit’s 15.4-inch height and 12.8-inch width. It also weighs more at 19 pounds versus 13.7 pounds. Both remain wall-mounted and compact.
Does the 27 kW heater provide more hot water?
Yes, it delivers a higher flow rate of 6.6 GPM. This supports busy households needing consistent heat for multiple fixtures. The 14 kW unit offers lower flow, suitable for single bathrooms. The 27 kW model provides nearly double the thermal energy for higher demand scenarios.
Are both heaters electric or gas powered?
Both units are electric tankless water heaters. They use cast aluminum heating chambers and self-modulating technology for efficiency. Neither requires gas lines or venting. They are ETL certified for safety and designed for wall mounting in residential settings.
Which model is better for a small apartment?
The 14 kW Thermomate model is better for small spaces. It offers precise control and efficient heating in a compact footprint. It fits single-bathroom setups or point-of-use needs where space is limited. The 27 kW unit is overpowered and physically larger for such applications.
Can I use the 14 kW unit for a kitchen sink?
Yes, it is excellent for point-of-use applications like a kitchen sink. It provides efficient heating for single fixtures. The compact size allows for easy installation under cabinets. It is not designed for high-demand multi-fixture use, so it works best when serving one specific location.
What is the difference in wattage between these two models?
The 27 kW unit provides nearly double the thermal energy of the 14 kW model. This higher wattage allows for greater flow rates and simultaneous use. The 14 kW model is sufficient for lower demand. Choose based on your household’s total hot water requirements.