Tankless Water Heaters in Maine: What They Need Electrically (and Whether Your Panel Can Handle One)
Thinking about replacing your water heater with an electric tankless model? The short answer is yes, it may provide endless hot water: but it can also place a major demand on your home’s electrical system.
Many homeowners in Saco, Biddeford, Portland, Scarborough, Kennebunk, Gorham, Windham, and nearby Southern Maine communities are surprised by how much electricity a whole-home tankless water heater needs.
Before you purchase a unit, it is important to understand:
How many amps the heater may draw
Why dedicated 240-volt circuits are usually required
Whether a 100-amp or 200-amp panel can support it
When service upgrades may be necessary
Whether gas, standard tank, or heat pump water heating may be a better fit
Our team at Downeast Electrical Services is here to help you make an informed decision before installation begins.
How much electricity does an electric tankless water heater use?
A traditional electric tank water heater usually stores hot water and reheats it over time. An electric tankless heater works differently. It heats water as it flows through the unit.
That on-demand heating requires powerful electric heating elements.
Most whole-home electric tankless water heaters operate at:
208 or 240 volts
Multiple dedicated circuits
Approximately 60 to 120 amps of total demand
Sometimes more, depending on the model and water-flow requirements
A larger unit may be rated between 18 and 36 kilowatts. As a simple example, a 24-kilowatt heater operating at 240 volts can draw approximately 100 amps:
24,000 watts ÷ 240 volts = 100 amps
Because water heating can be treated as a continuous load, the circuit and service design must account for the heater’s full demand and applicable sizing requirements.
This is very different from a standard electric tank, which may use one 240-volt circuit with a much smaller breaker.
Electric tankless heaters usually need multiple dedicated circuits
A whole-home electric tankless water heater is rarely connected to one ordinary branch circuit.
Depending on the manufacturer, the installation may require:
Two, three, or four dedicated 240-volt circuits
Two-pole breakers, often rated between 40 and 60 amps each
Separate cable runs from the panel to the heater
Proper disconnecting means for service and maintenance
Conductors sized to the manufacturer’s requirements and the applicable electrical code
For example, a unit may require three 40-amp, 240-volt circuits rather than one oversized breaker. Another model may call for two 60-amp circuits.
The exact requirements depend on the heater’s:
Kilowatt rating
Maximum amperage
Number of heating elements
Voltage
Manufacturer installation instructions
Distance from the electrical panel
Installation conditions
Do not rely on a general internet chart when selecting wire or breakers. The nameplate and installation manual for the specific model must be reviewed before any wiring is planned.
What wire gauge is typically required?
Wire size also varies by model and installation method. As general examples:
A 40-amp circuit may commonly require 8 AWG copper conductors
A 60-amp circuit may commonly require 6 AWG copper conductors
These are examples, not universal rules. Conductor sizing can be affected by insulation type, terminal ratings, ambient temperature, conduit, cable length, voltage drop, and the manufacturer’s instructions.
A licensed electrician will verify the correct wire gauge rather than guessing based only on breaker size.
Can a 100-amp panel handle an electric tankless water heater?
In most cases, a 100-amp panel is not a good match for a whole-home electric tankless water heater.
A 100-amp service may already be supplying:
Electric heat or baseboard heating
A range or cooktop
An electric dryer
A clothes washer
Refrigeration
Well or sump pumps
Air conditioning or heat pumps
An electric vehicle charger
Lighting and general receptacle circuits
If a tankless heater can draw 80 to 120 amps by itself, there may not be enough capacity left for the rest of the home.
That does not mean every 100-amp service is automatically disqualified. A small point-of-use heater may have much lower requirements. A detailed load calculation is the only reliable way to determine whether the existing service can support the planned equipment.
For a typical whole-home electric tankless installation, however, homeowners with 100-amp service should be prepared for the possibility of a service upgrade.
What about a 200-amp panel?
A 200-amp panel provides significantly more capacity and is commonly recommended for larger electric tankless water heaters.
However, a 200-amp panel does not automatically mean the installation will work.
Your electrician still needs to review:
The home’s calculated electrical load
Available breaker spaces
Existing large appliances
Heating and cooling equipment
The size and condition of the service conductors
The meter and service equipment
The tankless heater’s maximum demand
Planned future upgrades
For example, a 200-amp home with electric resistance heat, an EV charger, a hot tub, and an electric range may have less usable capacity than expected.
In other homes, a 200-amp service may have enough capacity for the water heater without further work. The answer comes from a load calculation, not simply from counting empty breaker spaces.
When does a service upgrade become necessary?
A service upgrade may be recommended when the existing electrical system cannot safely support the new water heater along with the home’s other loads.
The project may involve:
Replacing a 100-amp service with a 200-amp service
Installing a new main panel
Adding or replacing service conductors
Updating the meter equipment
Improving grounding and bonding
Adding an outdoor service disconnect where required
Installing additional dedicated circuits
Coordinating permits and inspections
Our service upgrade and panel services are designed to help homeowners understand these options before buying high-demand equipment.
In Maine, electrical installations commencing on or after July 1, 2026 must comply with the 2026 National Electrical Code, Maine amendments, and applicable local requirements. You can review the state’s adopted Chapter 120 electrical installation standards.
The 2026 code context is especially relevant when an installation includes a new service or major electrical work. Current load-calculation provisions should be applied, and the local authority having jurisdiction may have additional expectations.
Gas tankless versus electric tankless
Gas and electric tankless heaters can both provide on-demand hot water, but their installation requirements are very different.
Electric tankless advantages
Electric models may offer:
A compact wall-mounted design
No combustion gases
No gas line installation
No venting through an exterior wall or roof
Quiet operation
Straightforward fuel delivery through the electrical system
The challenge is the high electrical demand. In an older Maine home, the cost of new circuits and a service upgrade can significantly affect the total installation price.
Gas tankless advantages
Gas models generally use much less electricity. The electrical connection may only operate controls, ignition, and pumps.
However, gas units require careful planning for:
Gas-line capacity
Combustion air
Venting
Condensate drainage
Clearances
Carbon monoxide safety
Plumbing and fuel-system requirements
A gas tankless unit may be a better electrical fit, but it is not automatically the simplest or least expensive option. A qualified plumbing and heating professional should evaluate the complete installation.
Could a heat pump water heater be a better fit for your Maine home?
For many Maine homeowners, a heat pump water heater is worth considering before committing to electric tankless.
Heat pump water heaters still use electricity, but they move heat from the surrounding air into a storage tank rather than creating all the heat through resistance elements. As a result, they can use substantially less electricity than standard electric resistance heaters and electric tankless models.
Efficiency Maine reports that heat pump water heaters can save more than $500 per year in electricity compared with traditional electric water heaters. They also offer instant discounts and are commonly installed in Maine basements.
Potential benefits include:
Lower operating costs
Reduced electrical demand
A storage tank for household hot water
Dehumidification
Long warranties
Access to Maine efficiency incentives
Heat pump water heaters do need adequate space and airflow. They also produce some noise and cool the surrounding room. A basement or other suitable utility area is often a good location.
A standard tank water heater may also remain the most practical choice for some homes because it is familiar, widely available, and generally easier to connect to an existing electrical system.
What should you do before buying a tankless heater?
The best time to call an electrician is before purchasing the equipment.
Ask for a panel and service assessment that includes:
Identifying your existing service size
Reviewing the condition and available spaces in your panel
Checking the tankless heater’s model and nameplate
Calculating the home’s existing and proposed electrical load
Confirming the required breakers and wire sizes
Reviewing the installation location and wiring route
Determining whether permits or service upgrades are needed
Comparing alternatives such as a heat pump or standard tank
Our general electrical service includes panel inspections, load-balance checks, troubleshooting, and recommendations for additional work.
The bottom line for Southern Maine homeowners
Electric tankless water heaters can provide reliable, on-demand hot water, but they are electrically demanding.
The key points are:
Whole-home electric tankless heaters often require 240-volt dedicated circuits
Total demand is commonly in the 60- to 120-amp range
Larger models may require several 40- or 60-amp circuits
Wire gauge must follow the manufacturer’s specifications and code requirements
A 100-amp panel often cannot support a whole-home unit
A 200-amp panel may work, but only after a load calculation
Many installations require a service upgrade
Gas tankless systems reduce electrical demand but add venting and fuel-system requirements
Heat pump water heaters and standard tanks may be better suited to many Maine homes
Whether you are in Saco, Biddeford, Portland, Scarborough, Kennebunk, Gorham, Windham, Westbrook, or another nearby town, a licensed electrician can assess your system before you buy.
If you are searching for an electrician in Portland, Maine, comparing Maine electricians, or planning a Southern Maine electric project, contact Downeast Electrical Services for expert guidance. We can help you understand your panel capacity, plan the required circuits, and determine whether service upgrades make sense for your home.
The right water heater should provide comfort without overloading your electrical system. A professional assessment can make the decision seamless and hassle-free.
Stay tuned for more informative blog posts from us.
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