To install an electric tankless hot water heater, you will need to ensure your electrical panel has sufficient capacity, mount the unit, connect water lines, and wire the heater according to the manufacturer's instructions. This guide walks you through the process step by step, covering everything from tools and safety to final testing. Whether you are replacing a traditional tank heater or installing a new system, understanding how to install an electric tankless hot water heater correctly is critical for performance and longevity.
Tools and Materials Needed
Before beginning, gather the following tools and materials. Having everything on hand avoids unnecessary trips to the hardware store.
- Electric tankless water heater (sized for your home’s flow rate and temperature rise)
- Voltage tester and multimeter
- Pipe cutter or tubing cutter
- Adjustable wrench and channel-lock pliers
- Drill with appropriate bits for mounting
- Level
- Copper or PEX tubing, fittings, and shut-off valves
- Electrical cables (size per manufacturer specs), conduit, and connectors
- Circuit breaker(s) of correct amperage
- Teflon tape or pipe thread sealant
- Safety glasses and gloves
Safety Precautions
Working with electricity and water demands extreme caution. Always turn off the main breaker before opening the panel. Use a voltage tester to confirm power is off. Follow local codes; many jurisdictions require a permit and inspection. The International Association of Plumbing and Mechanical Officials (IAPMO) provides model codes that many US states adopt. Additionally, consult the U.S. Department of Energy’s water heating guide for efficiency recommendations.
Electrical Requirements
Electric tankless heaters draw high current—often 40–60 amps per unit, and some larger models require two separate circuits. Your electrical panel must have available breaker slots and sufficient service capacity (typically 200 amps for a whole‑house unit). If unsure, hire a licensed electrician. Use the table below as a general reference for wire sizing and breaker rating. Always check the manufacturer’s installation manual for exact specifications.
| Heater Wattage | Voltage | Minimum Breaker Size | Minimum Copper Wire Gauge (AWG) |
|---|---|---|---|
| 8,000 W | 240 V | 40 A | 8 AWG |
| 12,000 W | 240 V | 50 A | 6 AWG |
| 18,000 W | 240 V | 75 A | 4 AWG |
| 24,000 W | 240 V | 100 A | 3 AWG |
Note: These values are typical for US residential installations. Actual requirements vary by unit and local code.
Step‑by‑Step Installation
1. Mount the Unit
Select a location near the point of use (e.g., near the main bathroom or kitchen) to minimize hot water lag. The wall must be able to support the weight. Use a level to mark mounting holes, drill, and secure the bracket. Ensure clearance around the unit for ventilation and access.
2. Connect the Water Lines
Install shut‑off valves on both the cold water inlet and hot water outlet. Use Teflon tape on threaded connections. Connect the cold water supply to the inlet (usually marked with blue or “C”) and the hot water line to the outlet (red or “H”). Flush the lines before final connection to remove debris. For homes with hard water, consider installing a water softener to prevent scale buildup.
3. Run the Electrical Wiring
Run the appropriate gauge wire from the main panel to the heater location. Use conduit where required by code. Connect the ground wire to the unit’s ground terminal. Terminate the hot wires (L1 and L2) to the corresponding terminals. Do not turn on power until all connections are double‑checked.
4. Purge Air and Test
Open a hot water faucet downstream to allow air to escape. Turn on the cold water shut‑off valve and let water flow until a steady stream appears. Then close the faucet. Inspect all water connections for leaks. If leaks are found, tighten or reseal as needed. Once water tight, turn on the breaker and test the heater. Adjust temperature settings per the manual.
Common Mistakes to Avoid
- Undersizing the unit – calculate flow rate and temperature rise for your climate.
- Using wire that is too small – can cause overheating and fire risk.
- Forgetting to install a pressure relief valve (if required by local code).
- Neglecting to flush the system annually to remove mineral deposits.
If you encounter issues during installation, water heater repair professionals at MyTownPlumber can assist. For related plumbing concerns such as drain cleaning or leak detection, our team is ready to help.
Maintenance and Longevity
Regular maintenance extends the life of your electric tankless heater. Flush the heat exchanger with vinegar or a descaling solution once a year. Clean the inlet filter every few months. Check the electrical connections for signs of corrosion. With proper care, these units can last 20 years or more.
Frequently Asked Questions
Can I install an electric tankless water heater myself?
If you have experience with electrical and plumbing work, you may be able to handle the installation. However, many jurisdictions require a licensed electrician or plumber for code compliance. Incorrect installation can lead to fire, shock, or water damage.
What size breaker do I need for an electric tankless water heater?
Breaker size depends on the heater’s wattage and voltage. Typical units require 40 A to 100 A breakers. Always follow the manufacturer’s specifications and local electrical codes.
Do electric tankless heaters save money?
They can reduce standby energy losses compared to tank heaters, lowering your energy bills. However, upfront costs are higher. The U.S. Department of Energy estimates that tankless heaters can be 24%–34% more efficient for homes that use 41 gallons or less of hot water daily.
How long does installation take?
A professional installation typically takes 4–8 hours. DIY may take longer, especially if you need to upgrade the electrical panel or run new wiring.
Do I need a permit?
Most US municipalities require a permit for electrical and plumbing work, including water heater replacement. Check with your local building department.
Can I use existing wiring from my old tank heater?
Often no. Tankless heaters require much higher amperage, so the existing wiring is usually undersized. You will likely need to run new, larger gauge wire.
— MyTownPlumber Editorial Team
Ready to upgrade your water heating system? Contact MyTownPlumber today for a professional consultation and installation estimate. Our licensed technicians handle everything from pipe repair to sump pump services, ensuring your home’s plumbing runs efficiently.