To install a tankless electric water heater, you need to size the unit, run the correct gauge electrical wire, mount the unit, connect water lines, and test the system. This guide walks you through each step for a safe and code-compliant installation. Tankless electric water heaters save space and energy by heating water on demand, but installation requires careful planning and adherence to local electrical and plumbing codes.
Tools and Materials
Before starting, gather the following items. Having everything ready helps avoid delays.
- Appropriate gauge copper wire (typically #6 to #8 AWG, depending on unit size)
- Double-pole circuit breakers (sized per manufacturer specifications)
- Electrical conduit and fittings (if required by local code)
- Pipe wrench, tubing cutter, and deburring tool
- Copper or PEX water supply lines
- Shut-off valves and unions
- Temperature and pressure relief valve (T&P valve)
- Drain pan and drain line
- Mounting bracket and screws
- Voltage tester and multimeter
- Pipe thread tape (Teflon tape)
- Safety glasses and gloves
Step 1: Determine Electrical Requirements
Tankless electric water heaters demand high power. Most residential units require 240-volt service with multiple dedicated circuits. For example, a typical 27 kW unit often needs three 40-amp double-pole breakers and #8 AWG copper wire. Always consult the manufacturer’s installation manual for exact specifications. The U.S. Department of Energy’s water heating page provides general guidance on energy efficiency, but local electrical codes (based on the International Association of Plumbing and Mechanical Officials (IAPMO) standards) will dictate final requirements. Use a voltage tester to confirm that your panel can handle the additional load; you may need a service upgrade if your home’s electrical capacity is insufficient.
Step 2: Choose a Location and Mount the Unit
Select a wall near the main water heater location or close to the point of use. The unit must be mounted vertically with clearance for wiring and plumbing connections. Follow the manufacturer’s mounting template to secure the bracket to studs. Ensure the area is dry and protected from freezing. Unlike gas tankless heaters, electric models do not require combustion venting, but they still need a drain pan underneath to catch any leaks (connect the pan to a floor drain or run a drain cleaning line to the outside).
Step 3: Install the Electrical Circuit
Run the appropriate gauge wire from the main panel to the unit’s location. Use conduit where required. Connect each hot wire to a dedicated double-pole breaker, and attach the ground wire to the grounding bar. The following table shows typical wire and breaker sizes for common tankless electric water heater capacities. Note: Always verify with the unit’s manual and local codes.
| Unit Capacity (kW) | Number of Circuits | Breaker Size (Amps) | Minimum Wire Gauge (AWG) |
|---|---|---|---|
| 18 | 2 | 40 | 8 |
| 24 | 3 | 40 | 8 |
| 27 | 3 | 40 | 8 |
| 36 | 4 | 40 | 6 |
After connecting the wires inside the unit, double-check all terminal screws. Do not energize the circuit until the water lines are connected and the system is flushed.
Step 4: Connect Water Supply Lines
Install shut-off valves on both the cold water inlet and hot water outlet. Use unions to allow easy removal of the heater for service. Connect the cold line to the inlet (marked with blue or “C”) and the hot line to the outlet (marked with red or “H”). Wrap pipe thread tape on all threaded connections. Install the T&P valve on the hot outlet line or as directed by the manufacturer, and run a discharge pipe to within 6 inches of the floor. If your home has hard water, consider installing a water softener upstream to reduce mineral buildup inside the heat exchanger.
Step 5: Test and Commission
Open the shut-off valves and check for leaks at every connection. Turn on a hot water faucet to purge air from the lines. Once water flows steadily, turn off the faucet. Now energize the circuit by flipping the breakers on. Set the desired temperature on the digital display (typically 120°F to prevent scalding). Run hot water again and verify that the heater activates and delivers consistent temperature. Use a multimeter to confirm voltage at the unit terminals. If the heater does not turn on, check for tripped breakers or loose wiring.
Safety Considerations
Working with 240-volt electricity is dangerous. Always turn off the main breaker before working in the panel. Use insulated tools and wear rubber-soled shoes. If you are not comfortable with electrical work, hire a licensed electrician. The CDC’s plumbing safety resources emphasize the importance of proper backflow prevention and cross-connection control. Additionally, ensure the T&P valve discharge is directed safely to avoid property damage from pressure relief events.
When to Call a Professional
While some homeowners successfully install tankless electric water heaters themselves, many situations call for a licensed plumber or electrician. If your home’s electrical panel lacks capacity, if you need to run new conduit through finished walls, or if you are uncertain about local permit requirements, it is wise to call an expert. Incorrect installation can lead to fire hazards, water damage, or voided warranties. MyTownPlumber offers water heater repair and installation services, as well as leak detection to identify hidden problems.
Frequently Asked Questions
Q: Do I need a permit to install a tankless electric water heater?
A: Most municipalities require an electrical permit and sometimes a plumbing permit for new water heater installations. Check with your local building department. Failure to obtain permits can complicate home sales and insurance claims.
Q: Can I install a tankless electric water heater myself?
A: Yes, if you have experience with 240-volt wiring and plumbing, and you follow all codes. However, many homeowners hire a professional to ensure safety and compliance.
Q: What size breaker do I need for a 27 kW tankless water heater?
A: A 27 kW unit typically requires three 40-amp double-pole breakers. Always confirm with the manufacturer’s specifications and local electrical code.
Q: How long does installation take?
A: A DIY installation can take 4–8 hours, depending on the complexity of running new wiring and plumbing. Professional installation is usually completed in half a day.
Q: Do electric tankless water heaters need venting?
A: No, electric models do not produce combustion gases, so no venting is required. However, you must install a T&P valve and drain pan for safety.
Q: Will a tankless electric water heater save me money?
A: They can reduce standby energy losses by 24–34% compared to storage tank heaters, according to Energy.gov. Actual savings depend on usage patterns, local utility rates, and installation quality.
Installing a tankless electric water heater is a rewarding project that improves your home’s energy efficiency and provides endless hot water. If you need professional help or a second opinion, MyTownPlumber is here to assist. Contact us today to schedule a consultation or take advantage of our current offer: Click here for a special plumbing service discount.
— MyTownPlumber Editorial Team