How do you install an electric tankless water heater? The process involves mounting the unit, running the correct gauge electrical cable from a dedicated breaker, connecting the hot and cold water lines, and purging air from the system before powering on. This guide walks through how to install an electric tankless water heater safely and up to 2026 National Electrical Code standards. Always verify local amendments with a licensed professional—plumbing and electrical work require permits in most jurisdictions.
Why Choose an Electric Tankless Water Heater?
Electric tankless heaters are compact, energy-efficient, and can last 20+ years with proper maintenance. Unlike gas models, they don’t require venting or gas-line installation, making them ideal for retrofits in smaller US homes. The U.S. Department of Energy notes that tankless systems can be 24–34% more efficient than storage-tank heaters for homes that use less than 41 gallons of hot water daily.
Tools and Materials You Will Need
- Electric tankless water heater unit (sized to your home’s flow rate)
- Breaker panel and double-pole breaker (typically 60–125 amp, 240V)
- THHN copper wire (sized per manufacturer specs; usually 4–6 AWG
- Conduit and fittings (rigid or flexible metal)
- Copper or PEX water pipes (with shut-off valves
- Pipe wrench, adjustable pliers, screwdrivers, voltage tester
- Teflon tape, pipe-joint compound, and mounting hardware
Step-by-Step Installation Process
1. Choose the Right Location
Mount the unit indoors in a frost-free area—utility closets or basements work well. Leave at least 12 inches of clearance around the heater for airflow and future water heater repair access. Do not install in a bathroom or shower stall unless the unit is rated for damp locations.
2. Install a Dedicated Electrical Circuit
Electric tankless heaters draw very high amperage (often 80–120 amps). Run THHN wire from a main breaker panel through conduit to the heater’s terminal block. For a 240V circuit, the neutral wire is not needed unless the heater requires 120V for controls. Check the manufacturer’s documentation—the International Association of Plumbing and Mechanical Officials recommends verifying wire sizes against the National Electrical Code (NEC) Table 310.15(B)(16).
3. Mount the Unit
Secure the wall-mount bracket to studs with lag bolts. Lift the heater onto the bracket (two-person job for larger units). Confirm it is level and all screws are tight to prevent vibration noise.
4. Connect the Water Lines
Attach cold water inlet and hot water outlet using flexible braided hoses or rigid copper. Install isolation valves and a pressure-relief valve if required by your local code. Flush the line for 30 seconds to remove debris before final connection.
5. Wire the Heater
Turn the main breaker OFF. Remove the access cover on the heater and connect the incoming wires to the terminal block: black to L1, red to L2, and green or bare copper to ground. Torque connections to manufacturer specs—loose connections cause arcing.
6. Purge Air and Test
Open a hot water fixture in the house to release trapped air. Turn the water supply back on and check for leaks. Only after confirming no drips should you turn the breaker ON. Set the thermostat to 120°F to prevent scalding per CDC water safety recommendations.
Common Mistakes and How to Avoid Them
| Mistake | Why It's Dangerous | Fix |
|---|---|---|
| Undersized wiring | Overheating, fire risk | Follow NEC table and heater manual exactly |
| Skipping the pressure-relief valve | Can cause tank rupture | Install a T&P valve rated for the unit’s output |
| No sediment filter | Scale buildup reduces flow | Add a Y-strainer on the cold water inlet |
| Installing in unheated space | Freeze damage voids warranty | Use indoor-rated unit in conditioned space |
When to Call a Professional
If your main breaker panel doesn’t have capacity for a new 100+ amp circuit, or if you’re unsure about conduit sizing, hire a licensed electrician. For complex retrofits that involve re-piping from a storage tank, contact our team at pipe repair specialists. Tankless electric units often require upgrading the electrical service panel—that’s not a DIY task.
Maintenance Tips to Extend Heater Life
Flush the heat exchanger with vinegar solution every 12 months to remove mineral scale. Replace the inlet water filter seasonally. Hard water areas should consider a water softener to prevent efficiency loss. Annually inspect all electrical connections and tighten any that appear loose—corrosion can develop in humid basements.
Frequently Asked Questions
Can I install an electric tankless water heater myself?
Technically yes, but most municipalities require permits and inspection. Errors in wire size or grounding create serious hazards. Many manufacturers void the warranty if a licensed professional didn’t do the install.
What size breaker do I need for an electric tankless heater?
Typical US residential units require a 60–125 amp double-pole breaker. Exact size depends on the heater’s wattage and voltage. Always round up to the next standard breaker size per NEC 240.4(D).
Do electric tankless heaters need a neutral wire?
Most 240V-only units do not use a neutral—only L1, L2, and ground. Some digital models with displays require 120V for the control board, in which case a neutral is needed. Check the wiring diagram on the unit.
How long do electric tankless water heaters last?
With proper maintenance, 20–25 years. The heat exchanger is replaceable, extending lifespan further. Compare that to tank-style heaters that need replacement every 10–15 years.
What is the typical flow rate for a whole-house electric tankless heater?
A 27 kW unit delivers about 4–5 gallons per minute at a 45°F temperature rise in the US. For simultaneous showers and a dishwasher, you may need two smaller units or one 36 kW heater.
Is it worth switching from gas to electric tankless?
If you have solar panels or low electricity rates, yes. Electric has zero combustion emissions, no venting costs, and simpler installation—especially in homes without gas lines. However, initial electric panel upgrades can cost $1,500–$3,000 depending on your area.
Ready to upgrade your home’s water heating system? Get a free estimate from MyTownPlumber—we handle the permits, wiring, and plumbing so you have continuous hot water without the stress.
— MyTownPlumber Editorial Team