Electric Tankless Water Heater Installation Overview
Part of our Ventilation & Hot Water guides.
This overview explains the work so you can plan and talk to an electrician and plumber. Large electrical work should be done by licensed pros.
| Time | Half day (pros) |
|---|---|
| Difficulty | Pro recommended |
| Tools | Licensed electrician + plumber |
Step by step
- Load calculation. Electrician confirms panel capacity.
- Run circuits. Dedicated 240 V circuits with the breaker and wire gauge in the manual (e.g. 70 A and 6 AWG for 13.8 kW).
- Mount unit. Wall-mount near the point of use.
- Plumbing. Connect cold in and hot out with isolation valves.
- Purge air. Run water through before powering on to avoid burning elements.
- Power on and set. Set temperature and test every fixture.
Tips & common mistakes
- Never power the unit before it's full of water.
- Install isolation valves for future descaling.
Questions to answer before buying
- What is your main electrical service (100 A, 150 A, 200 A)?
- How many spare breaker spaces does the panel have?
- What is your coldest incoming water temperature?
- What will the heater supply: one sink, one bathroom, the whole house?
The answers determine whether you need an 8 kW unit on a single 40 A circuit or a 27-36 kW unit needing 2-4 large breakers.
Wire and breaker examples from VEVOR listings
- 8 kW: 40 A breaker.
- 13.8 kW: 70 A breaker with 6 AWG wire.
- 18 kW: up to 75 A current draw.
Follow the exact numbers in your unit's manual and local code.
Plumbing tips
Install isolation valves with service ports on the cold inlet and hot outlet so you can flush the heater later without cutting pipes. Mount the unit vertically, with clearance below for the valves. Use dielectric unions where copper meets steel fittings.
First start-up
Open a hot tap and let water run until all air is out before turning on the breakers. Running an empty element can burn it out in seconds.
Frequently asked questions
Can I install it myself?
Plumbing can be DIY for experienced homeowners; high-amp electrical work should be done by a licensed electrician.
Can a tankless heater be installed outside?
Electric units are typically indoor; outdoor installs need weather-rated models.
What size wire do I need?
Follow the manual; for example, a 13.8 kW VEVOR unit lists 6 AWG wire with a 70 A breaker.
Will my lights dim when it turns on?
If the service is undersized, lights may dim; a load calculation prevents this.
How long does a tankless heater last?
Often longer than tank heaters with regular descaling.