Your browser is out of date.

You are currently using Internet Explorer 7/8/9, which is not supported by our site. For the best experience, please use one of the latest browsers.

Products Electric Tankless On Demand Electric Water Heater

Tankless On Demand Electric Water Heater

Hubbell Seafare MHX/MTX And MTXA

Available up to 54 KW
Single or Three Phase Voltage

Request a Quote Hubbell MTX Brochure
model mtx


The Hubbell MTX Tankless model is a highly reliable and easily maintained electric water heater designed for operation in a marine application. The Hubbell MTX Tankless is compact, highly efficient, takes up minimal space, reduces operating costs. Hubbell's vast experience, meticulous engineering, and advanced manufacturing processes ensure that you can rely on the MTX Tankless for your water heating needs in even the most demanding and critical applications. It makes sense to specify and install a Hubbell MTX Tankless model for your heating requirements, and as the owner you will be provided with a quality product that is long lasting, trouble-free, and energy efficient.

Find a Rep


Marine Approvals

  • American Bureau of Shipping (ABS) Type Approved
  • ABS Approval eliminates costly delays and uncertainties during ship inspection

Heavy Duty Construction

  • Simple to specify and easy to operate
  • Factory wired electrical controls provide trouble-free installation and operation

Weight and Space saving

  • Significantly reduces weight and saves sapce compared to storage tank water heaters
  • On demand heating eliminates costly and cumbersome storage tanks
  • Instantaneous design reduces stand-by heat loss and lowers operating costs


  • Engineered for your specific application to ensure reliable operation
  • Constructed with high grade materials to ensure long operating life

How It Works

The Hubbell Model MTX electric tankless water heater contains high powered heating elements that heat water only when there is demand for hot water. When hot water is needed, a built in flow sensor measures the exact flow rate, and that data combined with temperature readings at the heater's inlet and outlet are processed by the electronic temperature controller. This data is continously transmitted to the temperature controller, which constantly calculates the precise amount of power (kW) needed to achieve the desired temperature. A zero cross over firing signal is sent to the fast acting triacs in order to modulate the heating elements to the precise level needed to meet demand. The Hubbell tankless heater uses only as much power as is needed, while delivering accurate and consistent hot water temperature.

Heater Overview

model mtx how it works


Heating ChamberCopper and Bronze
Capacities5 thru 54 kW
MountingBulkhead Mounted
Voltages208 thru 600 Volt 50/60 Hz
Phase1 Φ and 3 Φ (Balanced)
Power Factor0.999
Thermal Efficiency98% +
Inlet/Outlet Size:
MTX: 3/4" Dielectric Union Copper Sweat
MHX: 1" Dielectric Union Copper Sweat
Min/Max Flow:
MTX: 0.2 GPM Min, 8.0 GPM Max
MHX: 0.5 GPM Min, 40 GPM Max
Thermostat Range32-194°F / 0-90°C
Hi-Limit200°F (Fixed)
Design WP100 psi
Design TP300 psi
ElementsIncoloy 800
Standby Power< 3 Watts
Chamber Warranty5 Year
Electrical Warranty1 Year
EnclosureStainless Steel Brushed Finish
ApprovalscULus, UL EPH ANSI/NSF 5
Max Inlet Temp.: 150°F

General Specifications

Temperature Controller

A sophisticated electronic temperature controller with LED digital display provides the user interface. The temperature controller processes all flow and temperature data and calculates the precise amount of power needed to meet demand.

Operator Control Capabilities
CheckmarkPower Limiting:Allows the operator to reduce the power consumption by any percentage to provide installation and operational flexibility and savings.
CheckmarkDiagnostics:Display inlet and outlet temperatures, flow rate and error codes to assist in troubleshooting.
CheckmarkCost Calculator:Determine the exact cost of operating the heater. Input your cost per KW·Hr and the controller displays total KW·HRs consumed, total cost of operation, and total hot water usage (shown in gallons or liters).
CheckmarkTemperature Control:Set the digital display to the desired water temperature in °F or °C.  Fully adjustable in 1° increments from 32-194°F (0-90°C). A user adjustable +/- 3° calibration feature provides additional control for superior accuracy.

Full Heater Modulation

Each heating element is switched on/off using a fast acting solid state triac with zero cross over firing control. This switching schema provides full modulation of each heating element, ensuring that the precise amount of heat is added to meet demand. To improve operating efficiency and component longevity, each triac is mounted to a heat sink located on the incoming supply piping so that heat generated by the triac during the switching process is dissipated into the water.

Proper Power Integrity

All Hubbell tankless water heaters, including all 3 phase models, are engineered to operate as a balanced load and operate at 0.999 Power Factor. All Hubbell 3 phase models are designed for 3 wire (3 live, 1 ground) and 4 wire power systems and draw equal current across all conductors to maintain the power integrity of the users electrical system. Hubbell does not recommend the use of heaters that operate as an unbalanced load, as is common with staged heaters designed for star systems (3 live, 1 neutral, 1 ground) that require use of the neutral leg.  All load switching in Hubbell tankless models is performed as zero cross over, eliminating phase angle firing interference and associated EMI issues.

Full Resource Staging

The Hubbell tankless control schema ensures that usage is equalized across all heating circuits. To achieve this, once the controller has calculated the precise amount of kW required, all circuits are energized in a staggered fashion such that each circuit is proportionally and independently energized and then time staggered between circuits. This Full Resource Staging Schema reduces EMI output, increases component longevity, and provides highly accurate and consistent hot water temperatures.  For three phase models, all circuits are fully modulated and synchronized to operate as a balanced load.

Building Management Integration

Remote Control:Ability to remotely enable or inhibit the heating operation of the unit using one of the following two methods:
1. Customer supplied 24VDC signal is user configured for either Inhibit Mode or Normal Operation Mode.
2. Customer supplied volt free contact is user configured for either Inhibit Mode or Normal Operation Mode.

Priority Control: An integrated SPDT potential free dry contact (NO/NC 10A @ 240VAC) energizes when the unit is heating and de-energizes when not heating. This feature is useful when it is desirable to give the water heater priority over another electrical load to ensure that both are not operational at the same time.


Outline Dimensions and Model Selection

8-27 KW Models (2 and 3 Element)

model mse drawing
Model Selection Chart
0.2 - 8.0 GPM
0.4 - 40.0 GPM
Base Model NumberKW3 Phase Voltages1 Phase Voltages
Base Model NumberKW3 Phase Voltages1 Phase Voltages


















  • Chart indicates three element (3) and two element (2) model types
  • Additional 440V 3Φ sizes available including 5, 6, 7 and 13 KW

24-54 KW Modles (6 Element)

Model Selection Chart
0.2 - 8.0 GPM
0.4 - 40.0 GPM
Base Model NumberKW3 Phase Voltages1 Phase Voltages
Base Model NumberKW3 Phase Voltages1 Phase Voltages
MTX02424checkmark (6)

checkmark (6)

MHX02424checkmark (6)

checkmark (6)
MTX03131checkmark (6)
checkmark (6)

checkmark (6)

MHX03131checkmark (6)
checkmark (6)

checkmark (6)
checkmark (6)

checkmark (6)
checkmark (6)

checkmark (6)
MTX03636checkmark (6)
checkmark (6)checkmark (6)
checkmark (6)

MHX03636checkmark (6)
checkmark (6)checkmark (6)
checkmark (6)
MTX04040checkmark (6)
checkmark (6)

checkmark (6)

MHX04040checkmark (6)
checkmark (6)

checkmark (6)
checkmark (6)checkmark (6)checkmark (6)checkmark (6)
checkmark (6)
checkmark (6)checkmark (6)checkmark (6)checkmark (6)
checkmark (6)
MTX04848checkmark (6)checkmark (6)checkmark (6)checkmark (6)checkmark (6)checkmark (6)checkmark (6)
MHX04848checkmark (6)checkmark (6)checkmark (6)checkmark (6)checkmark (6)checkmark (6)checkmark (6)
checkmark (6)checkmark (6)checkmark (6)checkmark (6)
checkmark (6)
checkmark (6)checkmark (6)checkmark (6)checkmark (6)
checkmark (6)
Note: All models shown in this chart are six element (6) model types

Formulas & Charts

Heating Capacity and Amperage Chart

model mse formula table
Unshaded flows specify Base Model MTX, shaded flows must specify Base Model MHX due to high flow rate.
Alternate voltages including 277, 380, 415, 460 and 575 volt available. Please contact us directly for exact KW availability in these voltages.

Sizing Formulas

Step 1

KW Requirement:
________ GPM x ________ °FΔT x 0.1465 = ________ KW
Temperature Rise:
________ KW x 410 ÷ ________ GPM _________ °FΔT
Flow Rate:
________ KW x 410 ÷ ________ °FΔT = __________ GPM

Step 2

Choose the Tankless model with the KW rating which meets the peak demand (GPM) and required temperature rise (°FΔT) for your application.

Step 3

Choose the supply voltage available. Note the maximum amperage draw of the unit and verify availability.

Voltage De-Rating Factors

Rated VoltageApplied VoltageDe-Rating Factor
600 V575 V92%
600 V550 V84%
480 V460 V92%
240 V230 V92%
240 V220 V84%

When the actual supply voltage (applied voltage) is different than the design voltage (rated voltage) the resulting KW output will be affected. Please see the chart for typical voltage de-rating factors, or use the following formula.
(Applied Voltage² ÷ Rated Voltage²) x Rated KW = KW output at applied voltage


Optional Equipment

  • High flow construction specify model MHX for up to 40 GPM flow (min 0.5 GPM actuation)
  • Type 316L stainless steel heating chamber for added corrosion resistance
  • Special construction features available
  • Inlet/Outlet assembly simplifies installation and includes unions, shut offs, checkvalve, drain and pressure relief valve
  • NEMA 4x construction when heater is located in a wet environment. Overall dimensions 24" x 20" x 6"
  • Heating chamber built to ASME Section VIII and "UM" stamped
  • Remote Control Display allows the heater to be installed in remote location. The 3" x 5" NEMA 4 display enclosure can be located up to 250' from the heater and gives the operator full remote control and monitoring capabilities
  • Optional Inlet/Outlet union for connection to IPS pipe sizes. Specify customer connection as sil-braze or NPT
  • Special construction for use onboard Military Naval Vessels including shock, vibration and EMI qualifications
  • Factory supplied manifold single point connection for redundancy and high demand applications


What temperature should I set my water heater?

For typical domestic potable hot water service the temperature of your water heater at 125°F is sufficient. This prevents wasted energy (which means cost savings for you) and also decreases the possibility of scalding water burns. If you run out of hot water on this setting, increase the temperature by five degrees incrementally until your hot water needs are met. The goal is to have the temperature set just high enough to meet your needs but within safe operating parameters. Please note that a water heater in and of itself should not be relied upon as the ultimate temperature controlling source for the hot water delivered to your fixtures. Please consult local and state codes for installation of the proper and code approved (ASSE 1016, 1070, 1017) mixing devices to achieve the safe delivery of hot water to the fixtures. For a more complete information please download the whitepaper PDF titled "Understanding Potential Water Heater Scald Hazards" developed by ASSE at the following link ASSE Whitepaper

Which is better for me, a tankless or storage type water heater?

It depends. A tankless water heater is sometimes referred to as a Point-of-Use (POU) or instantaneous water heater. Due to the relative small physical size of a tankless water heater compared to a storage tank water heater, a tankless option can be advantageous from a space saving perspective and can sometimes be installed closer to where you want hot water (hence the term POU). However, tankless heaters are not suited for many applications, so it is critical that before choosing to go tankless you have carefully considered all of the factors that sometimes make the tankless option more complicated and risky compared to a storage type water heater. In particular, you should understand the operational characteristics, maintenance requirements, reparability, and sometimes significant installation requirements of a tankless water heater before making a decision. Tankless units do not store heated water like a storage type water heater; they only heat water as there is demand and therefore must be sized to meet the maximum flow for the application. In some cases a tankless water heater may improve operating efficiency, but possibly at the expense of user comfort. Hubbell tankless water heaters are available inElectric Tankless or Gas Tankless.

How does my water heater ship?

All Hubbell storage type water heaters ship via common carrier and are classified by the Commodity Classification Standards Board under National Motor Freight Classification (NMFC) class 100. Each water heater is palletized and wood crated. All Hubbell tankless water heaters, when transported using common carrier, ship class 77.5. To provide the lowest transportation cost, in most cases the shipment is made on Hubbell’s account and the freight cost is added to the invoice, commonly referred to as “Pre pay and add”. For very large shipments, the most economical method (LTL or Dedicated Truck) for transporting the water heaters to the final destination will be analyzed by Hubbell's transportation department.

Does the Hubbell electric tankless water heater restrict water flow?

No. Hubbell electric tankless water heaters do not restrict water flow. Other brands may incorporate a flow restrictor device within their tankless heater or require a flow restricting device be installed in the plumbing or fixture itself as a method for controlling temperature. This is not the case for Hubbell electric tankless water heaters.

How small is the Hubbell electric tankless water heater?

About the size of an average briefcase. The Hubbell tankless water heaters are a fraction of the size of a conventional storage tank type water heater and they mount on the wall, so you can reclaim 100% of the floor space once occupied by your conventional water heater.

Can the standard Hubbell tankless water heater be installed outside?

No. However, Hubbell does off an electric tankless model with NEMA 4 construction and is suitable for outdoor installation, please see Hubbell model TX.

What temperature should the tankless heater be set to?

The Hubbell electric tankless water heater can be configured by the user to operate in any of three different ranges. Low temperature range is 32-104°F, Standard range is 32-140°F and High Temperature range is 32-194°F. The operator can field configure the electronic controller to operate in any of these ranges, and can then select a set temperature within the selected range that is appropriate for the application. The controller is also field configurable for either °F or °C operation and visual display

What is the difference between gas & electric tankless water heaters?

The most obvious difference between gas and electric tankless water heaters is the energy source that is used. Gas tankless heaters use either Natural Gas (NG) or Propane (LPG), but also use electricity (120v) to power an internal fan and other controls. Electric tankless heaters operate using only electricity. Electric tankless water heaters operate at higher energy efficiency, in the case of Hubbell the thermal efficiency is 98%+, compared to gas tankless which ranges from Energy Factor ratings of 0.82 to 0.96 depending upon model. Electric tankless is more efficient in large part because gas tankless models operate by burning gas, which is harder to control than electricity and is less efficient due to heat lost in the flue exhaust. Gas heaters require exhaust and/or fresh air intake venting, whereas electric heaters do not. Please note that efficiency and operating cost are two different things, to determine operating cost one must consider their cost of energy and usage in addition to the operating efficiency of the heater. Gas tankless water heaters cost more to purchase compared to electric tankless heaters. When replacing a storage tank type water heater with a tankless heater, it should be noted that both gas and electric tankless require changes to the existing plumbing and wiring of the tank they are replacing. When installing a new gas tankless heater, most installations will require a new/upgraded venting and gas line. When installing a new electric tankless heater, most installations will require upgraded wiring to the heater and replacement of the circuit breakers in the electrical panel. The largest available residential and light duty commercial gas tankless water heater is 199,000 BTU/Hr, but the most common size has an output of about 123,000 BTU/Hr. After factoring for energy efficiency, this is equivalent to roughly 36 kW. By contrast, the largest residential/light duty commercial electric tankless water heater is 27 kW, which has an effective output of 91,000 BTU/Hr. In terms of operation and maintenance, a gas tankless heater is considerably more complicated to maintain and service compared to electric tankless. In addition, an electric tankless heater will provide more accurate and consistent hot water temperature throughout a full range of flow rates compared to a gas tankless heater. However, gas tankless heaters because they are available in larger BTU sizes can provide a higher hot water flow rate/temperature rise for very large installations compared to a standard electric tankless heater.

Can my tankless heater serve a fixture that has an anti-scald valve?

Yes. However, it should be noted that a tankless water heating system is generally set to a “just right” temperature, unlike traditional storage tank water heaters which generally overheat the water and require mixing down to achieve a “just right” temperature. Therefore, with a tankless heater you may have to adjust the anti scalding valve to the maximum setting due to the delivery of “just right” temperature water to the shower valve.

What is the life expectancy of the Hubbell tankless water heater?

Depending on the type of installation, usage and water quality, the Hubbell electric tankless water heater can last from 15 to 25 years. In a typical application when properly maintained a Hubbell electric tankless water heater should have no problem lasting 25 years or more.

Will I get instant hot water with a tankless water heater?

This is a common misconception of tankless water heaters. A tankless water heater does heat water on-demand instantly. Just like a tank water heater, it still takes the same amount of time for the hot water to travel through the pipes and flush out the standing water that has cooled down and is already inside the hot water plumbing. No matter what type of heater is installed, it will always take time for the hot water to travel through the plumbing before arriving at the fixture. The length of time it takes always depends on the length of the pipes, the amount of flow through the fixture and the water pressure. In general, a centralized water heater will require the most time to deliver hot water to the fixture, whereas a Point-of-Use water heater will deliver hot water to the fixture in the shortest amount of time.

Is Tankless right for my application?

It depends. Due to the relative small physical size of a tankless water heater compared to a storage tank water heater, a tankless option can be advantageous from a space and weight saving perspective and can sometimes be installed closer to where you want hot water. Tankless water heaters do not store heated water like a storage type water heater; they only heat water as there is demand and therefore must be sized to meet the maximum flow and temperature rise for the application. Therefore, before proceeding with a tankless heater you must carefully understand your application and review your available power. Hubbell offers a wide range of electric tankless marine heaters go to Electric Tankless for details. It is critical that before choosing to go tankless you have carefully considered all of the factors that sometimes make the tankless option more complicated and risky compared to a storage type water heater.

Which NSF Standard is appropriate for this product?

The appropriate NSF Standard to use is NSF 5, titled “Water Heaters, Hot Water Supply Boilers, and Heat Recovery Equipment”. In the past the lead content requirement was only required in NSF 61 per Appendix G, but within the past few years changes have been made such that Appendix G has been removed and replaced by NSF 372, “Drinking Water System Components – Lead Content”. NSF 5 requires materials approved by NSF 51, “Food Equipment Materials” and the latest edition of NSF 51 requires that the materials comply with NSF 372. Therefore, NSF 5 now complies with the same low lead requirements as NSF 61.

Can my heater ship via UPS?

Yes. Hubbell packages and ships this model water heater via United Parcel Service (UPS).

How is a tankless heater different from a storage tank heater?

A storage tank water heater maintains a tank full of hot water 24/7/365 and will heat water even during periods of no usage in order to make up for standby heat loss. A tankless water heater only consumes power (whether its gas or electric) when there is demand for hot water. They take up significantly less space and typically can be located close to the point of use, thus providing more efficient delivery of hot water. Tankless water heaters provide continuous hot water and never run out as long as the heater capacity is not exceeded.

Is 277 volt 3 phase voltage available for a water heater?

For all water heaters 277V is only an available option in 1PH, not 3PH. The 277V 1PH voltage is a derivation of your existing 480V 3Ph power. Where 480V is the line to line voltage on a 3 phase system and 277V is the voltage from any one of these lines to neutral, thus making the 277V power available in 1PH only.

Does Hubbell offer DNV certification?

Yes. Hubbell marine water heaters come standard with ABS Type Approval, but and are also available on request with other third party approvals including DNV, BV or NR-13.

Do Hubbell water heaters qualify as Low Lead?

Yes, all Hubbell water heater models qualify as meeting the low lead requirements of the “Reduction of Lead in Drinking Water Act” amendment to the “Safe Drinking Water Act” (SDWA) Section 1417(d) effective as of January 4, 2014. Hubbell certifies that its water heaters meet the following requirements of the SDWA and therefore are qualified and certified as Low Lead : (a)Hubbell water heater do not contain more than 0.2 percent lead with respect to solder and flux (b)Hubbell water heaters do not contain more than a weighted average of 0.25 percent lead with respect to all wetted surfaces of the water heater

What is the difference between solid-state and electromechanical relays?

Depending on the application, one switch may be more advantageous than the other. Please refer to this article to read more about the differences between solid-state and electromechanical relays.

Does my tankless water heater need a T&P relief valve?

Yes and no. NEC paragraph 422-27 requires all water heaters to be equipped with a temperature limiting device in addition to its control thermostat with the exception of instantaneous water heaters identified as being suitable for such use and with a capacity of 4L (1 gallon) or less. Hubbell tankless heaters are have a capacity of less than 1 gallon and are listed to UL Standard 499 which is recognized by NEC and thus meet the requirements of this exception. However individual state and/or local plumbing codes, such as Massachusetts and Kentucky, may require the installation of a temperature and pressure (T&P) relief valve. Therefore Hubbell recommends checking state and local plumbing codes for verification.

Is American Bureau of Shipping (ABS) approval needed?

Equipment and specifically water heaters for use in commercial marine applications require special construction features to ensure longevity and proper operation in a marine environment. In addition, the water heater must be constructed in conformance to the Code of Federal Regulations USCG 46 CFR Part 53.01 and the pressure vessel must be designed and constructed to the proper ASME code and stamped. A Hubbell marine water heater is manufactured under a Certificate of Manufacturing Assessment as issued by American Bureau of Shipping (ABS) Here

Technical Support

Our Technical Support Reps are ready to assist you. Please contact us today.


Contact Us

Request a Quote or Get More Information About the Hubbell Seafare MHX/MTX