Search waterheatertimer.org / all results
Search using Find button  

 Tweet button  

How to wire Tankless electric water heater

Stay safe.
Turn power OFF
FYI; Manufacturer's literature and side-by-side tests show that whole-house tankless electric water heater costs about $100 more per year to operate than ordinary tank-type heater.
Large research file
General troubleshoot .pdf

I have to read ? 
circuit breakers are warm
Do not install tankless electric if main box is overheated

Test if electric service panel is adequate for tankless:

1) Open following link to Stress-Test main breaker and service panel:  Main breaker stress test
Example: if you have 150 amp service, maximum load is 80% or 120 amps. Exceeding 80% causes main breaker to start getting warm. Over time, the breaker gets weak, and overheats on busbar, damaging panel. 
So if you add small tankless unit requiring 50-60 amp breaker, you might need larger service. Do the stress test.
Example:, if you have 200 amp service, maximum load is 80% or 160 amps.  So if you add whole-house tankless requiring 120-180 amps, you probably need up-size to 250 amp service depending on other household loads such as freezer, pool pump, oven etc.
2) To Figure amps for tankless: Read label on side of tankless for Volts and Watts. Divide watts by volts to get amps.
3) Add amps from tankless to service panel stress-test.

If electric service is too small, then install new service.
Or use ordinary tank-type heater and save your money, and headaches How to increase amount of hot water

Step #1/     Look at rating plate located on side of unit

1) Look at electrical rating plate showing voltage and wattage

2) Consult Tankless manual for cautions, and advisories
Failure to follow steps in manual will void product warranty
Some manuals do not have wiring diagrams: See wiring information below

3) Warranty Caution:
Do NOT call manufacturer and report installation is not correct, since that will inform them your product is out of compliance with warranty
The warranty covers defects in manufacturer's workmanship, but does not cover installer workmanship.

Overview of installation steps

Read the manual

Step #2/    Read the manual

Rheem Product Manual says:
"The voltage requirements and wattage load are specified on the rating plate on front of water heater."

Rheem Tankless electric manual
Rheem wire and breaker size chart

Bosch Tankless AE115, AE125 electric manual
Bosch Tankless AE3.4, AE7.2, AE9.5 manual
Bosch Powerstar manual

Bradford White QuickShot instantaneous has wire gauge and images of L1 L2 wiring terminals (and L3 terminals for 3-phase model)
Bradford White instantaneous

Tempra plus tankless electric water heater

Step 3: If tankless has factory-connected wire

Do not undersize wire and breaker
How to wire tankless electric
Larger image

Factory-connected wire/ or pigtail attached to tankless

Read rating plate on side of unit for amps and watts.
Connect wire from breaker and factory pigtail inside octogon box using wire connectors
This type of tankless will have 1 heating element.
How to select and install correct wire connector
Select correct wire and breaker size
How to wire 240Volt outlets
Main breaker warning

Screws on main breaker are HOT at all times
Even when main breaker is OFF, both screws are HOT
Only if meter is PULLED are these screws safe to touch

Step #4       Look inside tankless unit for wire connections

Single wire cannot be split apart to connect to multiple terminals.
tankless electric
This Example shows tankless supplied by 1 wire

I do not like this example because the wire is stranded and not solid copper wire.
Stranded wire carries fire risk.
Always use solid copper wire
Timer caught fire

Tankless MUST be grounded

Single 240Volt has L1 and L2

1) There will be single block with L1-L2 terminals
There will be 2 wires for connection made with wire connectors
Single wire cannot be split apart to connect to multiple terminals.
2) Look at rating plate on tankless to determine total watts
3) Use information on right to select breaker and wire size
4) Scroll down to see wiring examples for breaker
How to select and install wire connector
Titan N150 manual does not show wiring

If tankless has one set L1-L2 terminals, use single 240Volt wire.
L1-L2 terminals means 240Volt connections.
240Volt ratings:
 7680 watts / 40 amp breaker/ 8 gauge wire
 9600 watts/ 50 amp breaker/ 6 gauge wire
11520 watts/ 60 amp breaker/ 6 gauge wire
13440 watts/ 70 amp breaker/ 4 gauge wire
See amp chart
Rheem RTE9: use 40 amp breaker 8 gauge wire
ground wire not shown
Rheem wire and breaker size chart

2 wire 240Volt has 2 sets L1 and L2

Single wire cannot be split apart to connect to multiple terminals. Example:
Rheem RTE27: use two 60 amp breakers, and two 6 gauge wires
Rheem wire and breaker size chart
Ground wire not shown

If tankless has 2 sets L1-L2 terminals, then use 2 separate wires

Ground terminal wire not shown

3 wire 240Volt has 3 sets L1 and L2

Single wire cannot be split apart to connect to multiple terminals.
Separate wire needed for each set L1-L2 terminals

If tankless has 3 sets L1-L2 terminals, then use 3 separate wires

Ground terminal not shown

This example shows Tankless with terminal connections for 3 wires
Larger image

Example shows 3 wires connected inside tankless

Electricity supplied by 3 separate wires from 3 breakers
Total electric consumption for typical tankless electric is 96 to 120 amps.

Before installing tankless electric, look at main breaker on household service panel.
If main breaker is 150 amps, then it is max-ed out carrying this tankless load.
Breakers are rated safe maximum at 80%
Main breaker 150 amps x 80% = 120amps safe maximum

Tankless electric water heaters consume large amount of electricity
This is because electric elements cannot heat water as fast as natural gas or propane gas.
Tankless electric water heater will cost more to operate than ordinary tank-type electric water heater.
This is because so much energy is wasted trying to heat water as it passes quickly in pipe.

To reduce energy consumption, add a tempering tank to preheat incoming cold water, keep thermostat setting low, reduce consumption, lower water pressure, add low-flow shower heads.
If water moves too slowly through the pipe, tankless may not activate

Solid copper wire only

Why solid copper? Because stranded wire can come loose under the screw plate on tankless connection.
Why does stranded wire come loose? Because all wires get hot and expand when amperage is flowing to heater. Stranded wire moves around when it expands, causing the wire to come loose.
What happens if the wire gets loose uunder the screw terminals? The wire will start to arc and cause fire and melted terminal, and tripped breaker.
Solid wire rule applies to all screw terminals... timers, outlets, switches, relays etc.
Use terminal ends with stranded wire, or add solder to stranded wire to make solid.
Timer caught fire

Notes and cautions before wiring

1) Use only SOLID COPPER wire. Do not use aluminum wire. Do npt use stranded wire

2) Unit must be grounded

3) Install disconnect if breaker box is NOT within sight of Tankless water heater

4) Look for markings on wire terminals
Connect Hot to Terminals marked L1 and L2
Wire color does not matter. L1 and L2 can be either Hot wire
Connect ground wire to Green ground screw.
5) When white wire carries voltage, add black tape on each end to notify next electrician that voltage is present
It meets CODE to use Black-white for 240Volt -or- Black-Red for 240Volt -or- black and black
Adding black tape to White wire is for safety, and common electrical practice.
how to wire tankless
Larger image

Bosch examples/ shows wiring inside tankless

Bosch AE125 has 3 wire/
Use three 40 amp 240volt breakers, and three 8 gauge wires
Use #8 copper wire from each breaker (up to 100')
         Amp rating for each 40 amp breaker is 40 amps x 80% = 32 amps         
         This tankless electric will draw 3 x 32 amps = total 96 amps.

Bosch AE115 has 2 wire/
requires two 40 amp 240volt circuits
Use #8 copper wire from each breaker (up to 100')
        This tankless electric will draw 2 x 32 = total 64 amps

Connect wires to terminal block
Tankless must be grounded.

Step #5       Inside Main Breaker box

How to wire Tankless electric water heater
Electrical connection inside breaker box

Example: 3 circuit breakers inside main box

Breaker and wire size

Connect 3 #8 wires to 3 40-amp circuit breakers in main panel or subpanel
Safe Maximum for 40 amp breaker is 80% = 32 amps.
Safe Maximum for 8 gauge wire is 32 amps.

8 gauge wire for amp loads up to 32 amps.
Volts x amps = watts
240Volts x 32 amps = 7680 watts

Larger image of wire size chart
Main breaker box for tankless electric
Larger image

Three 50 amp 240Volt breakers

Bosch AE125 requires 3 50-amp circuit breakers
Use 50 amp breaker with 6 gauge wire
No difference if all breakers on same side of panel, or on diffferent sides.

Requires 250 Amp main breker, with size 250 wire from power transformer
Wire size chart

If you do not have minimum 250 amp service, then do not install Bosch AE125
If your service is smaller, then do stress test on breaker box, to find maximum safe load.
Stress test

Circuit breakers at Amazon
Shop Amazon - Industrial Electric Products
Main breaker warning

Main breaker warning

Screws on main breaker are HOT at all times
Even when main breaker is OFF, both screws are HOT
Only if meter is PULLED are these screws safe to touch
Install subpanel for Tankless electric
Larger image of 240 Volt subpanel
Image of 120V-240V subpanel

240 Volt Subpanel for Tankless electric

***White Neutral wire is not needed for 240Volt breakers.
Ground wire arriving from main panel can be connected to busbar at top of subpanel, or install a separate ground busbar lower on panel. Keep ground wires away from Hot connections and Hot busbars.
Sometimes it is easier to add ground busbar near bottom of subpanel so ground wires can be kept away from Hot connections.

Illustration shows how to install subpanel for adding more breakers to main panel
With tankless electric, install 150amp breaker/ replace any 2-pole breaker close to top of panel
Use 2/0 wires with 150 amp breaker
2/0 copper wire between main panel and subpanel, up to 100 feet.
Install 3 40-amp breakers in subpanel to supply each of three 240Volt #8 wires going to Tankless.
Read nameplate on Tankless for watt rating.
#8 wire for 240Volt loads up to 7680 watts
Use 50 amp breaker and #6 wire for 240volt loads above 7680 and less than 9600 watts
For example tankless with single wiring terminal, might require 9600 watts or more
See amp chart
How to install subpanel

*Neutral wire is not needed if subpanel is NOT going to have 120volt breakers.

Place subpanel within eyesight of Tankless to avoid disconnect requirement
Disconnect lets electrician cut power to Tankless unit.
Disconnect is for safety. Electrician or homeowner knows for certain when power is OFF.
Never touch leaking water heater or wet water heater unless power is OFF
Never run water pipes directly above tankless where leaking and condensation can drip on water heater.
If tankless flooded, disconnet power and replace water heater

Larger image

Option: Install meter on 120-240V subpanel

***White Neutral wire not needed for 240Volt breakers.
Neutral wire only necessary for 120Volt breakers
Illustration shows Neutral wire in event you want a 120V-240 subpanel
Meter will read all voltage that passes to subpanel

New and used electric meters
Buy subpanel:
Main lugs at Amazon
Siemens 125 amp/ 8 space at Amazon
Siemens 125 amp/ 12 space at Amazon

How to install electric meter on water heater or subpanel
How to get electric service

Difference between 120Volt and 240Volt circuits

Service panel (main breaker box) may have to be changed for Tankless electric
Tankless electric can draw 96 to 120amps.
This is almost maximum output for many household electric service panels.
Before installing tankless electric, look at main breaker on household service panel.
If main breaker is 60-100 amps, the service is too small for tankless with 3 heating elements.
If main breaker is 150-200 amps, then your service is max-ed out with tankless electric load.
Breakers are rated safe maximum at 80%
Main breaker 150 amps x 80% = 120amps safe maximum => this leaves 0-14 amps for rest of house
Main breaker 200 amps x 80% = 160amps safe maximum => this leaves 64-40 amps for rest of house
How to test max load on household main breaker

120Volt vrs 240Volt
Illustration shows difference between 120Volt and 240Volt wiring
240Volt breakers are twice as wide as 120Volt breakers
120Volt circuit has 1 Hot wire
240Volt circuit has 2 Hot wires
Read more about 120-240
See inside main breaker box

Step #5      Power cut-off -or- disconnect

30 amp safety cut off


Electrical Code may require disconnect at Tankless unit, if Tankless installation is not within view of  main breaker box
Call local electrician for specific local code

Buy non fused safety switch:
60 amp 2-pole safety switch
Pullout Disconnect at Amazon
Fusable pullout disconnect
2-pole 30 amp non-fusable safety switch/ power cut-off
2-pole 60 amp non-fuseable safety switch

Shop Amazon - Industrial Electric Products

Step #6   Protect with surge protector

Intermatic IG1240RC3

Whole house surge protector

Tankless electric water heater is not protected from surge
Appliances, water heaters, timers, circuit breakers are not protected from surge
Most appliances today have electronics. Few of these appliances are protected from surge
Water heaters the plug into outlet are not protected from surge
Homeowner insurance might have appliance exclusion. Read policy
Water heater warranty does not cover surge event.
Protect 120V and 240V circuits with whole house surge protector
How to wire whole house surge protector
Intermatic IG1240RC3 whole house surge protector/ pdf

Other considerations:

Tankless save space

Installed behind furnace to save space!!!

Atta boy. Now you're thinking!!?
How you going to work on it?
Leave space for delime requirement.
Rheem-De-lime-tankless/ pdf
Tempering tank

Think about freezing temperatures

Locate tankless in naturally warm location
Tank-type heaters are warm full time.
Tankless will only heat with water demand.

Add tempering tank to passively preheat incoming cold water.
Add power to tempering tank in winter.
Some tankless will not activate if incoming temperatures exceed set point. Check product manual, and selle

Double check wire size and distance

100'-150' etc requires larger diameter wire

Select correct wire and breaker size

Step #7       Water pressure/ crossover/basic maintenance/pre-heating water

Water pressure should not exceed 80 psi

Connect pressure gauge to spigot
For example
200 psi Rain Bird P2A or 100 psi Brady BTG 100
Use pressure reducing valve and expansion tank on incoming cold water line
Water pressure gauges
Temperature-pressure gauge
Safety Equipment for Professionals
Industrial and scientific Amazon
Clogged water lines/ Low water pressure
Tankless flow rates

Tankless require good flow of water to activate element or burner

Crossover problem.
When single handled faucet has bad cartridge and cold water enters hot water line, reducing flow of hot water
Symptoms include: luke warm water temperatures - hot water never arrives
Read about crossover

Low flow shower heads etc
Restricted water flow can cause tankless not to work
Read about low water pressure
Tankless will clog with sediment

Tankless cannot be exposed to more than 11 grains hardness in water

Efficiency will decline within months.
Parts such as pressure sensor will fail within 2 years
De-liming will not prevent failure
Warranty does not cover failure due to water problems
Bradford White study
Water softener research pdf
Sediment in tank-type heaters
Delime tankless
Larger image

Delime tankless yearly

Tankless cannot be exposed to more than 11 grain hard water
How to de-lime tankless/ pdf
You can buy whole new tank-type heater for $200-300 and forget deliming every year.
How to delime tankless

Deliming will not restore full efficiency. Read research
How to delime tankless water heater
Maintain water heater 2012/ pdf
Rheem-De-lime-tankless/ pdf

Buy project materials
Tankless flushing kits
Tankless service valves
Submersible pump
Filter washers at Amazon
Washing machine hoses at Amazon

Clean water filter monthly

Warranty does not cover failure due to water problems
Read typical maintenance pdf
Take a shower

Tankless recirculation

How to install Tankless recirculation
How to solder pipes
How to maintain water heater
Exapnsion tank, pressure reducing valve, pressure gauge
Support the economy:
Buy water heaters  from my associate links:

50 gallon Gas water heaters at Amazon
40 gallon gas water heaters at Amazon
50 gallon Electric water heaters at Amazon
40 gallon electric water heaters at Amazon
Hybrid / heat pump/ water heaters at Amazon

How to install gas water heater
How to install electric water heater
Troubleshoot gas water heater
Troubleshoot electric water heater
Point of use water heaters
Troubleshoot Gas valves with manuals
Icon gas valve

Install and troubleshoot garbage disposal Waste King disposal
Install point of use water heater

How to wire tankless electric
Point of use water heater

Anode rods anode rods
Recirculation system

Tankless recirculation
Point of use water heater
Type 1 and type 2 surge protection surge protection

Gas and electric water heaters Buy
Industrial electric

Industrial supplies

Tools and home improvement

Lab and scientific
Buy Tools
Black and Decker
Saws and saw blades
Compare box timers
DPDT timers
Control water heater w/ Z-wave

Intermatic control centers Resource:
Control centers:
+ manuals and parts

All control centers and parts

Including Z-wave
programmable timer Resource:
Compare programmable timers
Compare countdown timers
Delay timers

Din rail

Enter Amazon from my links

E-mail: geno03245w@gmail.com
My response might end up in spam folder, check email folders
Privacy policy
Author page/ My Books