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How to wire water heater thermostats
Upper and lower thermostats
thermostat temperature range
Buy residential upper and lower thermostats

Thermostats are interchangeable/ each works with your water heater
Buy 90-150° F for residential tank:
Water heater thermostats at Amazon
Camco thermostats at Amazon
More thermostats
89T short/ dual-element thermostat at Amazon
Example Camco dual-element thermostat at Amazon
Commercial water heater thermostatsBuy commercial upper and lower thermostats
Buy commercial thermostat 120-180 degree F
Camco 120F to 180F thermostat (commercial grade only)
Camco 180F lower thermostat (commercial grade only)
Read more about 3-phase water heater

Residential tank thermostat is rated 90-160° F
Residential tank is NOT rated for pressure and temperature of 170-180° water.
Only use 180 F thermostat on commercial water heater that is rated for high temperature
Only use 180° F thermostat on commercial water heater that is rated for high temperature

Marathon water heater is rated 170° F
Thermostat for 3-phase non-balanced water heaters up to 480 Volt
Resource
How to change 3-phase water heater to single phase
All brands of thermostats are interchangeable

$48
for 2 low density 240 Volt 4500 watt elements/  + Upper and lower thermostat


Buy LOW density kit:
Apcom plumbers pack Amazon
110°-160°
Resource
How to replace elements

$35 for 2 high density 240 volt 4500 watt elements + Upper and lower thermostat

Apcom thermostats
Buy HIGH density kit:
Apcom plumbers pack Amazon
110°-160°
Resource
How to replace elements


Low density elements might last longer in hard water 
$45 for 2 low density 240 Volt 4500 watt elements/+ Upper and lower thermostat

Therm-o-disc thermostats
Buy LOW density kit:
Therm-O-disc low density plumbers pack
90°-150°
Resource
How to replace elements

New water heaters have high density elements.
$45 for 2 high density 240 Volt 4500 watt elements/ + Upper and lower thermostat

Therm-o-disc thermostats
Buy HIGH density kit:
Therm-O-disc high density plumbers pack
Therm-O-disc high density
Therm-o-disc high density / copper element
90°-150°
Resource
How to replace elements
NON-simultaneous water heater thermostats

See larger
Residential dual-element water heater
Both elements are never 'on' at same time unless tank is wired for other purpose (see owners manual). This is called 'non-simultaneous operation' since both elements are not 'on' at same time.

Either upper element is 'on' or lower element is 'on,' or both are off.

Buy thermostats from my affiliate links
Water heater thermostats at Amazon

Resources:
How to replace thermostat
How residential water heater works
Troubleshoot electric water heater
See inside main breaker box
Water heater pilot light
3-phase water heaters
Convert 3-phase water heater to single-phase

Test upper thermostat
Adjust temperature using screwdriver
How to adjust temperature/ gas and electric water heaters
How to replace thermostats
Whirlpool energy smart wiring
Larger image
Whirlpool energy smart with electronic thermostat
Many new water heaters are going to have electronic thermostats
Purpose is for manufacturer to sell proprietary parts available only from them
Higher prices.
End DIY
Cut out competitors who can sell generic parts
Resources
Whirlpool energy smart features and information
Convert energy smart to regular water heater
Two water heaters
Larger image
Non-simultaneous thermostats control 2 water heaters
Simultaneous wiring will heat top of tank first.
Redundant will turn ON as soon as cold water enters tank. 
How electric water heater works

Purpose:
 Add additional tank so more hot water available at peak times, without adding additional wiring.

Heater #1 must be satisfied before power is sent to heater #2.
Heater #2 may not fully heat before heater #1 needs to turn ON again. This will happen IF water heater is poorly insulated or cold water is drawn from heater #1 or incoming water is very cold.

Sequence is basically same as above.

Water heaters with foam insulation may require long drill bit from home center or fry's to bring wire to top of tank. Be sure insulation and covers are put over thermostats so thermostat not exposed to cool temperatures and cause temperature misread.
Buy 
72" drill bit from Amazon
Fish bits

Resource/ more wiring options:
Read about two water heaters with more wiring options
Why does this work?
240volt water heaters have two hot wires from breaker. Each element is permanently connected to one hot wire, and will always test hot for 120Volt to ground.
Thermostat opens and closes second hot wire to element. This action turns element ON-OFF
Basic water heater circuit
Thermostat is either Hot on T2 or Hot on T4, but never both.
Some ECO thermostats are numbered 2 and 4.
So the lower thermostat on water heater #1 will either send power to lower element on heater #1, or it will send power to heater #2.
Water heater #2 will not turn ON unless water heater #1 is OFF
When water heater #1 turns OFF, then heater #2 has 240V power available.
Take apart thermostats
See larger
How to make lower thermostat using upper thermostat
If water heater has foam insulation, then replacing lower thermostat with ECO protected thermostat may not be easy.
Take apart upper thermostat and make new lower thermostat that will work for the specific two-water heater diagrams shown above.

When not to use:
Do not remove ECO protection on upper part of tank.
On simultaneous and single-tank off-peak water heaters, the ECO is require for lower thermostat operation.
ECO protects you in case of overheating and is required for safe operation of water heaters.
Single element thermostat
Same thermostat used for both 120V or 240V
/ For correct voltage of water heater, look at label on side of tank
Upper Thermostats
Single-element thermostat         Dual-element thermostat 
2 screws on right side           3 screws on right side  
See Larger           
You CAN use dual-element thermostat for single-element tank
You CANNOT use single for dual tank
  
Single element thermostat/ 120V or 208V or 240V 
Same thermostat works for all voltages
Screw numbers are 1 thru 4
Single-element is identical to dual-element thermostat, except all dual-element upper thermostats have 3 screws located on right side.
You can use dual-element thermostat for single-element tank
You cannot use single-element thermostat for dual-element tank, unless tank is being rewired for redundant and simultaneous operation.
Wiring illustrations:
American thermostat                    American thermostat wiring
See Larger 240 Volt single                            See Larger 120 Volt single
Resources:
How to add indicator light to thermostats
How to replace thermostats

How to test elements
How to replace elements
Off -peak water heater thermostats
Off-peak thermostat wiring Purpose of off-peak ... save energy during peak electric prices.  
> Upper thermostat operates normally to keep top 2/3 tank hot.
> Lower thermostat heats bottom 1/3 of tank when ordered by off-peak meter or timer

Compare:
Off-peak water heater thermostats
Ordinary water heater thermostats

1. Lower thermostat replaced with ECO-protected thermostat identical to upper thermostat. ECO safety red reset cuts off power when water in tank reaches dangerously high 150-180°F

2. Upper thermostat: Red wire is moved L4 to T4. Color of wires can be different.

3. Black wire from lower thermostat does not connect to upper thermostat T4 screw
4. Black wire from lower thermostat runs to top of water heater for connection to off-peak meter, or off-peak timer

5. 240 Volt potential exists between yellow wire and each black wire at top of water heater

See Off-peak operation sequence
See more OFF-peak options
Off peak with two water heaters
Off peak 120Volt
Tork DTU timer Off peak operation
Larger image
Tork DTU timer OFF peak
Wire water heater so lower part of tank is OFF during peak price times.
Less hot water is available.
Tank is cooling during peak price, and probably will not run unless hot is drawn from tap

How to wire Tork DTU timer
How to wire thermostats
How electric water heaters work
EH40
Off-peak water heater timer
Off peak water heater timer
Lower thermostat receives power only when timer orders > Upper thermostat receives power full time

Resource:

How to wire off-peak water heater to timer
Simultaneous water heater thermostats
Simultaneous water heater wiring/ both thermostats operate independently
Used in large water heaters when elements cannot keep up with demand, or in high demand situations.

Lower thermostat replaced with ECO protected thermostat.
Each thermostat is wired separately.

Additional wire from breaker box required
Each thermostat wired to a separate circuit breaker, since each element draws 4500 to 5500 watts.
Wattage appears on end of each element
Figure wire and breaker size

Turn up thermostat temperature to get more hot water
Ways to increase amount of hot water

California restaurant code requires 9000 watt (9K) simultaneous water heater certified by manufacturer.
They do not allow rewire of residential tank since manufacturer will not certify.
Restaurant must buy commercial simultaneous water heater costing $1500 to $3000
Read Restaurant water heater sizing
9000 watt water heater
Simultaneous DC water heater Simultaneous DC water heater
Read how to convert AC water heater to DC/ high voltage
Convert AC water heater to DC/ low voltage

Meter on water heater
The Kwh meter is din rail mounted inside enclosure.
 
Buy
240 volt pass through Kwh  meter
2T2502GA beige plastic enclosure
2T2500GA grey plastic enclosure

Resource:
Enclosures
Simultaneous water heater wiring Simultaneous water heater wiring/ both thermostats operate independently
Upper and lower thermostats and elements work independently from each other.
Increased first hour delivery of hot water
Faster recovery time

4500Watt elements, then total wattage is 9000 watts.
Use 50 amp breaker and #6 gauge wire
or two 30 amp breakers and two 10 gauge wires

5500Watt elements, then total wattage is 11,000 watts
Use 60 amp breaker and 6 gauge wire
or two 30 amp breakers and two 10 gauge wires

Oversizing breaker and wire runs cooler and is more efficient

Off-peak
Connect lower thermostat to timer and convert water heater into off-peak operation.
Water heater companies are integrating their products with future smart-grid. Except they are installing electronic thermostats. Consider whole house surge protection
Whirlpool's (American/ AO Smith water heater) new 'energy smart'

The era of generic off-the-shelf parts is coming to an end quickly as companies try to boost sales by using proprietary parts that must be ordered from them.
SO buy extra parts and water heaters now.
Change water heater temperature using timer
Larger image
Change water heater temperature using GM40 timer and simultaneous wiring
Not necessary to increase wire or breaker size for this diagram
Use timer for two different temperatures on electric water heater.
Applies to GM40 timer and Tork DTU timer and GE 15207 timer etc
Either upper thermostat and element have power or lower thermostat and element have power. But not both at same time.

Install ECO-protected thermostat for lower thermostat.
Both upper and lower parts of tank are ECO-protected from overheating
Rewire tank so upper and lower parts are separate.
Use GM40 timer to switch power between lower and upper parts of tank.

Normal operation, the lower thermostat and element receive power and keep tank at temperature set point. Upper thermostat and element have no power.
This is called 'redundant' water heater operation. This technique for heating tank more rapidly after cold water first enters tank.

When timer activates, power to lower part of tank turns OFF. Power to upper part of tank begins. Upper thermostat is set for higher temperature.
Since tank is at regular temperature, the higher setting means upper element will turn ON and begin heating tank to higher set point.


Use this technique to heat water very hot for laundry cycle.
Disadvantage: The lower part of tank will cool rapidly as new cold water enters tank, so this technique is good for making short-term batches of hot water.
CA3750 off-peak water heater
Two 30 amp breakers required
Larger image
Z-wave contactor: 
1) Off-peak water heater  
2) simultaneous water heater 
3) change water temperatures 
4) water heater timer 
Set different scenes to utilize all 4 choices
Resource:
How to set and wire CA3750 Zwave contactor

water heater element
Wires attach to either screw on element:
Resources:
How to test elements
How to replace elements
Reset button
Resources:
How residential water heater works
How to replace thermostats on electric water heater
How to replace thermostats on gas water heater
Troubleshoot electric water heater
Troubleshoot gas water heater
Buy thermostats
Water heater thermostats at Amazon
Resource pdf files:

AO Smith bulletin: Thermostat wiring diagrams
 Rheem thermostat and element wiring diagrams
Bradford White thermostat and element wiring including 3-phase, single phase etc
American water heater thermostats and troubleshoot
State water heater thermostat and element wiring

Marathon thermostat and element wiring
Craftmaster thermostat wiring
Whirlpool 2012 electric water heater thermostat wiring
3-phase electric water heater service manual
Redundant thermostats: Only lower element operate


Step 1:
Remove blue and yellow wires from upper thermostat
Step2:
Move black wire from terminal T4 to terminal T2
Tighten screws very tight against copper wire.
Step3:
ECO protected thermostat must remain at top of tank to protect against overheating event.
Redundant thermostat

Upper element is disconnected.
Lower element heats tank.
Water heater responds immediately when cold water enters tank.
Can possibly cause more stacking events

Both thermostats control lower element.

When upper part of tank cools, the lower element turns ON. Hot water rises.
When lower part of tank cools, lower element turns ON.
ECO-protected thermostat must be kept at upper part of tank to avoid overheating event that can damage or rupture tank, cause scalding, release of hot water through TP valve and distill chemicals out of the water.


Cold enters lower part of tank through plastic dip tube.
Homeowners should check with plumber before altering water heater wiring. See insurance data on water heater failure
Redundant thermostats control 2 water heaters
Two water heaters Additional tank in series to double available hot water at peak times
See wiring option below
Read about two water heaters
Reduntant thermostats - two water heatersLarger image Redundant thermostats control 2 water heaters

Purpose:
Add additional tank so more hot water available at peak times, without adding additional wiring.

Heater #1 must be satisfied before power is sent to heater #2.
Heater #2 may not fully heat before heater #1 needs to turn ON again. This will happen IF water heater is poorly insulated or hot water is drawn from heater #1 or incoming water is very cold.

Sequence:
1) Power  from circuit breaker arrives at ECO-protected upper thermostat on heater #1
2) ECO protection might be required on upper part of tank to prevent overheating event since heat rises
3) Typical lower thermostat on heater #1 is replaced with ECO thermostat so power can be transferred to heater #2 when heater #1 thermostats are satisfied.
4) Once heater #1 is satisfied, power goes to heater #2.

Either heater can be wired for redundant or typical non-simultaneous operation.
The key is adding ECO-protected thermostat to lower part of heater #1, and adding wire from lower thermostat so power can be transferred to heater #2.

Water heaters with foam insulation may require long drill bit from home center or fry's to bring wire to top of tank. Be sure insulation and covers are put over thermostats so thermostat not exposed to cool temperatures and cause temperature misread.

Read about two water heaters
wire water heater thermostat How to change wiring / foam-insulated tank
Rewire foam insulated  tank
Drill through top of tank near wiring cavities
Keep drill bit near outer edge of tank shell

Buy
36" drill bits

Resource:
How to re-wire electric water heater
  WHQ water heater timer If you cannot rewire water heater because of foam insulation or other factors such as warranty:

Re-plumb water heaters in series, and run additional 30 amp circuit to additional heater. Then put both water heater on a timer
Both water heaters turn on-off at same time

Resources
WHQ4 Water heater timerSee basic water heater circuit
How to wire WHQ timer and GM40 timer
Water heater timer for two water heaters
More box-type water heater timers
3-phase water heater thermostats
Convert 3-phase balanced to 3-phase non-balanced for residential use has moved to another page
Resource:
3-phase water heater
480 Volt timer
Larger image
Timer for 3-phase water heater
208, 240, 277, 480 etc
See 3-phase timer wiring

Or convert 3-phase non-balanced to single phase/ shown on 3-phase water heater
Resource:
3-phase water heater
3 phase non-simultaneous water heater
Larger image
3-phase non-simultaneous 
Unbalanced
Both elements are never ON at same time.
Always use ECO-protected thermostat on upper and lower
Elements will heat with any applied voltage
Each element has volts and watts listed on side.
Volts squared divided by watts = correct ohm rating to test if element is good.
3-phase water heater service manual

Buy commercial grade 3-phase thermostat for 3-phase non-balanced water heater
Camco 120F to 180F thermostat with reset button at Amazon (commercial grade only)
Thermostats for residential water heater 90F to 150F at Amazon

Identify unbalanced water heater: it looks just like ordinary tank-type heater and does not have metal large box with contactors attached to front of unit.
3-phase balanced water heater has large box attached to front of unit.
 
Unbalanced means that 1 leg of the three phase carries greater load than other two legs. So this is just ordinary single-phase water heater except few wires moved so there is a 3-wire connection on top of unit. Difference is that 3-phase non balanced will usually have larger wires and breaker and elements.

Unbalance water heater uses ordinary 2-pole element and thermostat, except thermostat can be rated for 40 amps at 240Volts, and 30 amps at 480 volts
Ordinary hardware store thermostats are rated 30 amp at 240V.
3-phase thermostat at Amazon
40 amp 240V thermostat at Amazon
pdf file see page 7

Balanced load, means all three legs carry equal load.
Balanced water heater uses element with connections for 6 wires.
Illustrations for balanced: see lower on page
Wire water heater for 3-phase
Larger image
Another image slightly different wiring: larger
3-phase simultaneous 
Unbalanced. 
For example: 
L2 50 amps, L1 and L3 29 amps, depending on each element etc

Compare with non-simultaneous shown above: Move Red wire from T4 on upper thermostat to L1 on upper thermostat
Either element can turn ON, as temperature varies top and bottom of tank
Always use ECO-protected thermostat on upper and lower
Elements will heat with any applied voltage
Each element has volts and watts listed on side.
Volts squared divided by watts = correct ohm rating to test if element is good.

3-phase simultaneous current load

Heavy-duty commercial water heaters:
Balanced 3-phase 
Commercial electric water heater troubleshoot
Commercial electric water heater part diagnosis
3-phase electric water heater manual
3-phase water heater information has moved to another page
Resource:
3-phase water heater
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

Resources:
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
Resources:
Troubleshoot Gas valves with manuals
Icon gas valve

How to replace water heater element Waste King disposal
How to wire tankless electric


Install point of use water heater
Titan tankless

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Type 1 and type 2 surge protection surge protection
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Woods timers
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Tankless recirculation
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box timers Resource:
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