replace water heater element
Replace element
Use element wrench/ heat with torch
\Resource:
Remove rusted/stuck element

How to select & replace water heater element

With information about buying elements  -and-  How to clean sediment out of tank

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Dry fire/ warranty

If tank is not full of water... and no water is covering element when power is turned on => the upper element will burn out immediately => called dry fire.
Upper elements dry-fire. Lower elements do not dry-fire .... on ordinary residential 2-element tank.
When tank is filled with water, then upper element turns on first... and lower element does not receive power until top of tank is heated.
If upper element dry-fires, then upper part of tank is not heated, so power never gets to lower part of tank. Lower element does not dry-fire.
Warranties do not cover dry-fire.
Be sure tank is full of water before turning power ON. When filling tank, open tub spout on hot side. When water flows from tub spout, then tank is full.
Replace water heater elementsBasics for selecting element
Look at watts and volts printed on end of each element.

Volts: Match volts shown on element with volts shown on label on side of water heater. Do not install 120V element on 240V water heater or the 120 volt element will burn out.
Watts: Label on side of tank shows volts and watts for upper element & lower element & total connected watts (max wattage consumption of appliance)
When selecting element, buy same wattage or less wattage... keep volts the same.
It is ok to install higher watt up to 5500 on 4500 watt heater if breaker is 30 amp and wire is 10 gauge. It is ok to install lower watt: replace 4500 with 3500 as long as voltage is same. Lower watt means less heat, so element can last longer.
Some tanks have higher wattage on upper element, and lower wattage on lower element... might save money

240 volt 4500 watt element heats about 21-40 gallons per hour. 240 volt 3500 watt heats about 16-30 gallons per hour. Assumes full 240V is present.
240 volt 4500 watt elements will produce 3800 watt  at 208 volt
Residential water heaters are non-simultaneous as shown on product label. This means upper element is ON -or lower element is ON -or both elements are OFF - but both upper and lower are never ON at same time -unless wiring is changed to meet other objectives

Resources:
Figure volts amps watts for water heater
How electric water heaters work
How to wire thermostats
Increase amount of hot water
Identify water heater element

Buy smaller wattage or same wattage element?

Larger wattage voids product warranty, plus possible fire hazard.
Smaller wattage will NOT void product warranty.
Smaller is better: will cause electrical breaker to run cooler, and element and breaker last longer.
Smaller wattage will heat water less quickly.

Resources:
240Volt / 4500 watt element heats 21 gallons per hour; 3500 heats 16 gallons per hour  See chart
Clean old elements using white vinegar
Elements are sold at local hardware or home center, or on-line. Buy extra to keep on hand.
See ways to increase amount of hot water
High density element


Low density element
Screw-in elements
Elements burn out frequently?  
Buy low watt density or buy lower wattage

1) Density: All new water heaters come with high density elements. You can replace with high or low density as long as watts and volts are same.
Watts/ square inch = density.
Low density element resists burnout
Low density foldback elements including Camco 5-year warranty elements (shown below) are for problem water with high mineral content.
No loss of efficiency or faster heater by choosing either low or high density.
Lower watt density tend to last longer. Lower wattage can also last longer

2) Use smaller watt element will resist burnout by keeping temperature lower
Strategy: Change 4500 watt element to 3500 watt.
If circuit breaker is 20 amp, then 3500 watt elements are correct choice

Buy:
Low density element 
Low density element
See Low, medium and high density image

Camco elements
Use 1-1/2" socket
$25 - $47
Ultra low watt density
5 year warranty
Ultra Low Watt Density/ ripple
Hard water element
Resists high mineral count
Minimum 13-15" diameter tank
Buy: 240 volt:
4500 watt
4500 watt 13" diameter
5500 watt
Ripple elements
Camco ripple elements
Camco elements
Reliance 5500 watt ripple

Voltage of element must match incoming voltage from circuit breaker..

30 amp breaker and 10 gauge wire are good for elements up to 5000 watts.

If tank label shows 4500 watt, then installing higher wattage 5000 watt element might void product warranty.
Why? One reason, the factory installed wires inside tank are 12 gauge, that are too small for 5000 watt.
$13 - $26
Ultra low watt density
5 year warranty
Ultra Low Watt Density/ foldback
Hard water element
Resists high mineral count
Check minimum tank diameter
Fits any tank above minimum dia
Buy: 120 volt
1500 watt 120 volt 8" minimum
Buy: 240 volt:
2500 watt 
3500 watt
4500 watt 
5500 watt

Warranties do not cover dry fire (electricity ON before tank is full of water).
Resource:
Read about dry fire/ pdf page 2
$10 - $16

Low watt density
Camco/ no extended warranty
Low Watt Density/ foldback

Check minimum tank diameter
Fits any tank above minimum dia
Buy: 240 volt:
2500 watt
3500 watt
4500 watt
4500 watt 12 pack
5500 watt

6000 watt / 17" minimum tank/ use 8 gauge wire

Elements on this webpage are rated for AC voltages.
AC elements with work with DC
But Thermostats will melt with DC
$10 - $12
Low watt density
Camco/ no extended warranty/
High Watt Density
Standard on all new water heater
Can use foldback as replacement
Match volts and watts
Check minimum tank diameter
120 Volt point-of-use water heater
Buy: 120 volt:
1000 watt 120 volt 8" tank diameter
1400 watt 120 volt
1500 watt 120 volt 8' tank diameter
1650 watt 120 volt 7.5" minimum
1750 watt 120 volt 9" minimum
2000 watt 120 volt 9" minimum

Buy: 240 volt
1500 watt 
2000 watt 12 pack
2500 watt
3000 watt
3500 watt
3800 watt
4000 watt
4500 watt
Camco Universal flange/ & Flat flange
Including small tank,  point-of-use water heater elements
Universal flange high density
Camco/
5 year warranty
Low density foldback
Hard water element
Resists high mineral count
Buy: 240 Volt
4500 watt 240 volt
5500 watt 240 volt

Warranties do not cover dry fire (electricity ON before tank full of water).
Resource:
Read about dry fire/ pdf page
Universal flange high density
Camco/ no extended warranty
Foldback
Minimum Tank diameter varies
Buy: 240 Volt universal flange
4500 watt 12 pack
4500 watt 240 volt 9" diameter

Buy: 240 Volt flat flange
4500 watt 240 volt 13" tank

Hatco booster heater elements
Buy:
Hatco elements
Hatco 480 volt elements
Universal flange high density
Camco/ no extended warranty
High density
Minimum Tank diameter varies
Buy: 120 Volt 6-9" diameter tank
1500 watt 120 volt 9" tank
2000 watt 120 volt 9" tank
Buy: 240 Volt
1500 watt 240 volt 8" tank
2500 watt 240 volt 10" tank
3000 watt 240 volt 12" tank
3000 watt flat flange 14" tank
3500 watt 240 volt 14" tank
4500 watt 240 volt 13' tank
4500 watt 240 volt 15" tank
Convert flat flange element to screw-type element
Larger image/ uses 3/8" screws
Convert flange to screw-type
Convert round, flat and universal
For any standard water heater
Buy:
Camco adapter kit
Reliance adapter kit
Rheem adapter flange
Resource:
How to install adapter kit /pdf page 2
Rheem elements
Use 1-1/2" socket
Resistored element is unique to Rheem which claims longer life because resistor is added. No science supports the claim of longer life, but resistorized might resist dry-fire.
Low watt density
Resistored
Rheem/ no extended warranty
Low Watt Density/ foldback
Buy: 240 volt/ resistored:
4500 watt resistorized 
6000 watt resistorized

Resistored elements

Buy: 208 volt:
2000 watt 208 volt
208 volt elements

Buy: 480 volt (can be used single-phase or 3-phase element non-balanced):
4500 watt 480 volt
5500 watt 480 volt
6000 watt 480 volt
480 volt elements


Buy: 277 volt:
6000 watt 277 volt copper
6000 watt 277 volt stainless
277 volt elements
Low watt density
Low watt density
Rheem/ no extended warranty
Low Watt Density/ foldback
Minimum 14" diameter tank
Buy: 240 volt/ copper non- resistorized:
4500 watt copper 240 volt

Buy: 240 volt/ stainless steel non- resistorized:
4500 non-resistorized Amazon
5500 non-resistorized Amazon


Rheem elements


Rheem/ no extended warranty
NON-resistorized copper
I know of no advantage of copper vrs stainless steel or other materials
High Watt Density

Buy: 120 volt copper:
2000 watt 120 volt

Buy:: 240 volt copper:
1500 watt 240 volt
2000 watt 240 volt 
3000 watt 240 volt
3000 watt 240 volt
5500 watt 240 volt
Camco element socket

Use 1-1/2" socket to remove elements

Buy:
Camco element socket
Tekton water heater socket
Deep impact socket

$20
Breaker bar
$7
Ordinary Residential element wrench

Today's hex-head elements have rounded corners, and thinner profile. Making it difficult to hold wrench on element while turning.
Socket is easier to use than ordinary element wrench.
Use weight of water: Loosen element while tank is full of water. Then drain tank before unscrewing element.
Elements + Thermostats kits
Therm-o-disc and Apcom style and other type thermostats are interchangeable
Buy:
Camco (commercial only)
Camco (commercial only)
Commercial has higher temperature range that exceeds tank rating for residential water heaters

Resource
How to replace thermostats

Foldback/ low density
240 volt 110°-160°


Buy: low density kit:
Apcom plumbers pack Amazon
Water heater thermostats Resource:
How to replace thermostats



High density
240 volt 110°-160°

Apcom thermostats
Buy: high density kit:
Apcom plumbers pack Amazon
Water heater thermostats 
2 high density 240 volt 4500 watt elements
+ Upper and lower thermostat

All brands of thermostats are interchangeable
Resource:
How to replace thermostats
High/ low density options
240 volt 90°-150°
Therm-o-disc thermostats
Buy: low or high density kit:
Therm-O-disc low density plumbers pack
Therm-O-disc high density plumbers pack
Therm-O-disc high density
Therm-o-disc/ copper element
2 low or high density 240 Volt 4500 watt elements/
All brands of thermostats are interchangeable
Resource:
How to replace thermostats

Rheem marathon element
Rheem marathon element
Use 1-7/8 element wrench
1.5" UNF not 1" NPSM
12-14 threads per inch vrs 11.5
Read parts .pdf before buying
Buy:
1-7/8" water heater element wrench
SP610160/ 4500 watt copper
SP213670/ 4500 watt

SP210197/ 3800 watt
SP210201/ 3000 watt
SP210198/ 3800 watt
SP213480/ 3000 watt
SP213540/ 2000 watt
SP610130/ 3800 watt
SP213820/ 3800 watt
SP610140/ 5500 watt
SP610150/ 3000 watt
Resource:
Marathon parts sheet/ pdf
element thread to pipe thread            

Elements are 1" straight thread/ 

11.5 threads per inch/ Convert element port to 1" pipe thread
Adapt element NPSH straight thread to NPT pipe thread
NPSM thread

Buy:
1x1 
Suburban 1440 watt element
1" NPT stainless nut

Stainless 1" nut/ 

11.5 threads per inch/ Convert element port to 1" pipe thread
Adapt element NPSH straight thread to NPT pipe thread
NPSM thread

Buy:
1" NPT nut 
Water heater element

Identify Element wattage and voltage

Watt rating of tank appears on label on side of tank
Match same watt rating of new and old elements. Smaller wattage is ok. Larger wattage is not ok.
Product warranty, and electrical safety code, support same-wattage or smaller-wattage element.
Do not use larger wattage element than shows on water heater label.

12 gauge wire and 20 amp breaker, use max 3800 watt element
10 gauge wire and 30 amp breaker, use max 6000 watt element
What size wire do you have? Buy short pieces 10 and 12 gauge wire and compare with your wire
Resources:
Choose wire and breaker
Figure volts amps watts for water heater
Water heater is tripping breaker
Reset button

1) Before replacing element: Press reset button and see if heater works

Press reset button. Put ear against tank and listen for bubbly fizzing sound
If reset button will not reset and lock in place, then  replace thermostat
If reset keeps tripping, then element might be one cause: read reset keeps tripping
Resources:
How to replace thermostat
Buy water heater thermostats 

2) Before replacing element: Reset circuit breaker

Push breaker fully OFF and then fully ON
If breaker will not reset, then elements might be the problem, move wires to another same-size breaker like dryer circuit
If water heater works fine on different same-size breaker, then replace breaker: read how to replace circuit breaker
If breaker resets but keeps tripping, then elements might be the problem: read water heater is tripping breaker
Resources:
Water heater is tripping circuit breaker
How to replace circuit breaker
Test electricity

3) Before replacing element: Test if water heater is getting Voltage

Low voltage can cause less hot water
Test across top two screws on upper thermostat
Tape tester leads to wood sticks... keep hands away from live power
If voltage does not show on tester, then power coming to water heater is suspect

4) No Hot water / Less Hot water can be bad element/ or bad thermostats

Test elements as shown below. If elements check out, then replace thermostats
If upper element is bad, there will be no hot water

5) Very hot water can be shorted element/ or bad thermostats

Test each element screw to metal tank as shown below
If elements are OK, then replace thermostats
Resources:
How to replace thermostats
Troubleshoot resources

6) Before replacing element: Test element

Less hot water and no hot water indicate possible element failure, or thermostat failure, or low voltage etc. Test elements.
Requires multimeter/ power is off/ do not drain tank/ remove wires from element/ takes 10 minutes
Look at volts watts printed on end of element/ Put battery in multimeter/ Set multimeter to read ohms/ Ω symbol
No wires on element. Test for ohms across both screws on element/ volts squared divided by watts = ohms
Test for ohms between each screw and the steel tank/ should read zero
Resources:
Step by step: How to test elements
Buy multimeter 
Larger image

7) General troubleshoot

If there is some hot water, then upper element is good. Test lower element.   Action:  How to test water heater element
If both elements are good. Action: Push reset button, reset circuit breaker before replacing both thermostats
Overheating, or very hot water: Action: test both elements before replacing both thermostats. Read more
Reset button keeps tripping: Action: test both elements before replacing thermostats. Read more
NO hot water: Action: Press reset button. Fully reset circuit breaker, test both elements. Read more
New water heater, or repaired water heater not working: Read action
If voltage is reduced, then watt-consumption of element is also reduced. This can cause hot water shortage: Read more
More resources:
How to remove stuck element
How to test water heater element

Replacement and clean out start here
tools
Larger image
Get tools ready:
Flashlight, long water hose, washing machine hose, voltage tester, duct tape, cordless screwdriver, flat tip screwdriver, phillips screwdriver, channel locks (big pliers)
Replacement element, element wrench
Short hoses for vacuuming out sediment
Shop vac and extension cord... remove bag and filter from shop vac so it will work with wet sediment from water heater
220 Volt circuit breaker Step 1: Turn power OFF

Never assume power is OFF/ Test for power
Always check for power before starting.
Use non-contact voltage tester on wire, on outlet, on timer, on element, on thermostat etc to see if power is present.
Press button on tester, if single beep then no power is present.
If continuous beep then power is present.
Use at top of heater... use it at each element

Safety: Never stand on bare soil or wet surface, always stand on dry boards, do not hold or touch anything metal when working on timer or water heater that has power, tape tester leads to wood sticks, never touch wet water heater, or flooded water heater, or timer that had a short or fire without turning power OFF.

Buy:
Multimeters 
Simple multimeter/ Test continuity or voltage
Buy non-contact voltage tester 
Electric testers

Resource:
How to test if water heater electricity is off






Test water heater
See larger
Hose cap Step 2: Remove hose cap using channel locks
 Hose cap prevents drips
Have one ready, in event valve leaks when finished
Righty tighty/ lefty loosey
Rotate hose cap counter clockwise to loosen
Buy:
Hose caps on Amazon
clean out water heater tank Step 2a: See if tank will drain
 Do NOT turn off water <> full pressure is needed

Connect garden hose to water heater.
Put hand on the white valve ... as if it was a door knob... then ...
Rotate tank drain counter-clockwise to open.
See if water comes out end of hose.
Wait...
Do Not drain tank yet

Weight of water inside tank will hold tank in place when loosening element.
clogged water heater Clogged drain?
Connect washing machine hose to water heater drain-valve <> Connect garden hose between outdoor spigot and washing machine hose <> turn on outdoor spigot for a few seconds so water pressure flushes tank open

Resources:
What to do if water heater will not drain
How to replace drain valve
My house: images of garden hose and washing machine hose
water heater shut off valve Step 3: Turn off cold water
Turn off water going into water heater.
Do this by shutting off water valve just above water heater -or- close main shut-off valve to house

This will stop all hot water going to each faucet
bathtub faucet Step 4: Open tub valve ON HOT SIDE only
This will release hot water pressure
This will let air into line so water heater will drain
Leave tub valve open so at end of job you know when tank is full of water before electricity is turned back on.
Step 5: Remove outside cover, inside insulation, and plastic element cover
Cover and insulation must be put back when finished.
Otherwise thermostat will not read correct temperature.
thermostat covers Step 5a: Remove plastic thermostat covers
Upper and lower parts of tank use different cover
Start by unlatching cover at top
Some covers also latch on each side, while other slide off
Purpose of cover is to prevent electric hazard when adjusting temperature while power is ON
Make sure power is OFF when performing this step... use non-contact voltage tester
89T thermostat kit
Buy:
Upper element terminal protector
Lower element terminal protector
Resource:
How to replace thermostats

See Larger
Step 6: Check for Burned wire melted parts 
Use nose to check for burned smell.
Use eyes to look for burned and melted parts
Damaged wire can be caused by sediment filling bottom of the tank and then overheating element.

Resource:
How to test water heater wires
Cut back damaged wire
Any damaged wire must be repaired
Use wire nut to extend wire if necessary
Usual wire size for inside of tanks is #12 solid copper wire/ never replace with stranded wire
Test wires

How to test water heater wires
water heater element wrench    
Step 7: Choose Element wrench or socket
Lightweight 1-1/2" element wrench available hardware store, home center, plumbing supply
Best is 1-1/2" socket
I use socket because it grabs the element easier

Buy:
Water heater element socket 1-1/2" 
Heating element wrenches 
Camco heavy duty element socket
Marathon elements are 1-7/8"
electric impact wrench for elements Optional purchase:
Electric impact wrench for elements
Use for removal of element only.
Do not tighten element with impact wrench

Buy:

Impact wrenches 
Special 1-1/2" socket for elements
1-1/16" impact sockets
remove water heater element Step 8: Do not drain tank yet
SLIGHTLY Loosen element while tank is full of water

Loosen element SLIGHTLY while tank is FULL
Weight of water will hold tank while you twist wrench
Turn element wrench counter-clockwise
Must push on wrench to keep it in position on element, or wrench will slip off
Do not remove element -or- water will flood out hole
Next step, drain tank.
Also good time to check anode rod
How to replace anode rod
How to remove stuck element/ open the link
Torch, WD40, drill bolt holes and remove with wrench, use impact wrench
Make sure water heater is full of water / for weight / when loosening element
Resource:
Remove rusted/stuck element
Step 9: Drain tank
Open drain valve located at bottom of tank
remove old element Step 10: Remove element and old O ring --- after tank is drained
Take out old element
Element will have rubber ring that seals the tank. Remove O ring and element.

Before going further,
Check inside tank for loose pipe coming from top <> broken dip tube causes reduced hot water and wasted electricity

Resources:
Dip tubes
Anode rod
wet-dry vacuum Step 11: Assemble shop vac and hoses
Remove bag from shop vac so it will operate as wet vac
I use the hoses that are shown on left.
The element opening is 1" in diameter    
Garden hose bends into tank
     3/4" PVC is nice fit with garden hose
     1" clear tube fits 3/4" PVC
     30" piece of 1/2" CPVC reaches back of tank
Check there are no holes in the hose so you get good suction

Resource:
My house: image of my shop vac

Buy:
Wet dry vacs 

clean out water heater tank
Step 12: Vacuum out tank
Tape hoses together with duct tape.
Clear package tape also works. Masking tape does not work.
Turn vacuum ON. Insert hose or pipe. Move hose or pipe around. Remove and clean end of hose or pipe as needed.

Clear tube is handy
Length of 1" clear tube lets you see if sediment is flowing past. Sediment is a slurry of water and calcium carbonate that clogs the pipe easily <> so it's handy when you can see when the stuff is flowing past.

Short piece of garden hose bends into tank.
Use 1/2" cpvc to break up debris
Protect carpet from rusty water
Buy:
Duct tape from Amazon/ best seller
Shop vacs 
It doesn't have to be perfect
It will not be perfect... that's ok
Buy
Tank rinser 

Resource
How to clean tank and household pipes with bleach
How to maintain water heater
o ring on water heater element Step 14: Check new element & O ring
Put new O ring in place
Use new O ring> Do not re-use old O ring

Test new element if you want:

Resource:
How to test element for continuity
old element washer
See Larger
install water heater element Step 15: Clean opening and install element
Wipe off around opening.
Do NOT use teflon tape or any sealant > not necessary unless tank is damaged
install new element Step 16: Tighten element
Don't over tighten, a firm snug is enough
water heater element Step 17: Attach wires to either screw
Tighten screws very tight against copper wire
Only solid copper wire, No insulation under the screw head
Note: the burned wire was cut back and replaced with good copper wire and with solid insulation
Step 18: Close drain & put covers on
Close drain <> put cover and insulation on <> turn on water
Do NOT turn power ON until tank is full of water
Insulation must be reinstalled over thermostat
Do not turn on circuit breaker until tank is full of water

Drain valve drips???  Use garden hose cap if drain valve drips
Buy brass garden hose cap 
Resources:
How to replace drain valve
Water heater drain cap If drain will not stop dripping: add brass hose cap
Pick up plastic hose cap at local big-box-store, and replace later with brass hose cap

Buy:
Brass hose caps 
Water heater element
Wait to turn on breaker
Wait
Do NOT turn power On .....  until tank is full:
Wait for tank to fill
Water heater elements must be immersed in water or they will burn out instantly
Burn out is called dry fire, and is not covered by element warranty.
Replace burned out element with new element.
Step 19: Wait for tank to fill
Open bathtub spout ON HOT SIDE only
After water heater fills with water, water will start to come out bathtub valve
40 gallon tank might fill in 15-20 minutes or less
Tub is running on HOT side. Tank is full.
Bathtub hot water side is running with no air gaps <> turn off tub <> momentarily open TP valve on water heater to bleed last of water <> turn on circuit breaker
Step 20: Turn power On\
Push breaker FULLY off, the FULLY back on.
Turn on breaker <> put ear against water heater <> bubbly fizzing sound says it's working <> wait 10 minutes to see if water is getting hot.
Put EAR against side of tank and listen for bubbly fizzing sound
4500 watt tank heats 21 gallons per hour
240 volt, 40 gallon tank, with 4500 watt elements will take 2 hours to heat completely
Step 21: Clean out shop vac/ 
Let vac dry before putting lid on
Hang up hose so it will dry/ shake out hose a few days later
Shop vac must be cleaned out
Put debris in a bucket so it will dry
Calcium carbonate is not harmful to environment
Job is finished
Step 21: What if tank is not working?
Read 'repaired water heater is not working'

Meter on water heater
The Kwh meter is din rail mounted inside enclosure.
Records billable power usage in Kwh. Multiply by rate you pay per Kwh to get monthly/ yearly cost of running electric water heater.

Buy
Bomain power meter
240 volt pass through Kwh  meter
2T2502GA beige plastic enclosure
2T2500GA grey plastic enclosure

Resource:
Enclosures
How to install electric meter on 240Volt water heater
Flush tool
tank rinser

Buy plastic tank rinser

Works with ball valve/ must replace drain valve
Resource:
How to replace water heater drain valve
Buy
Tank rinser 
Durable 3/8" x 10-3/4' poly tube with short 45 degree bent end/
Overall length 11-1/2"
Connect to water hose
water heater ball valve
Water heater drain valve

Replace Water heater drain valve with ball valve

Easier flush and clean out
Full open position lets you insert 1/4" copper pipe flushing tool
How to replace drain valve

Buy parts:
Dielectric nipples 
3/4" ball valve 
Brass ball valve
3/4" pipe to 3/4" garden hose
Buy  Ball valve/ gas
Gas ball valve
Use 6 wraps teflon tape on threads
Shop Amazon - Industrial and scientific
circuit breaker resources

Circuit breaker resources

Water heater is tripping breaker
How to replace circuit breaker
How to wire gfci
Can AC breaker be used for DC breaker
How to reset circuit breaker
Not enough space for circuit breakers/ use tandem
Circuit breakers
How to install subpanel
Why you need ground wire
See inside breaker box
How to wire safety switch
How to wire whole house surge protector
Figure volts amps and watts
Figure correct wire and breaker
Types of surge protection

Connect water heater to different voltage?
If voltage is higher than element rating, then element burns out.
   Connect 277 volt or 480 volt to element rated 240 volt 4500 watt, and elements burn hotter and burn out
   Connect 240 volt to element rated 120 volt 1500 watt element, and element burns 4x hotter or 6000 watts and burns out
If voltage is lower than element rating: then element heats less water per hour
Connect 208 volt or 120 volt to element rated 240 volt 4500 watt element, and elements burn cooler and heat less hot water per hour
Connect 120 volt to element rated 240 volt 4500 watt element, and element burns 1/4 power and heats at 1125 watts. Good for off-peak or generator.
Resources:
Connect water heater to 120 volts
Connect water heater to generator
3-phase balanced element
3 lead or 6 leads on each element, depending on Delta or Wye.
Wye can have 3 leads, and Wye or Delta can have 6 leads
3-phase has 3 Hot wires arriving from breaker box
3-phase has A B C hot leads

Basically there are 3 elements in one.
Each element pulls same amps so load is balanced.

Contrast: Unbalanced 3-phase water heater has 2 ordinary elements.
Hot A feeds 1 leg of element 1, Hot B feeds 1 leg element 2
Hot C feed 1 leg of element 1 and 1 leg of element 2.
3-phase water heaters
Any 2-wire element 208 240 277 480 Volt can be used on commercial water heaters that are rated single-pole or 3-phase un-balanced.
Balanced delta, wye, 3-and-6-wire 3-phase elements are not covered here.
See wiring for 3-phase balanced

3-phase elements/ 3U
Buy:
3U Bundled Elements 

Resources: for 3-phase elements
Unbalanced 3-phase: 3-phase non-balanced elements are same as elements shown above
See wiring for 3-phase non-balanced
Balanced 3-phase: Commercial 3-phase balanced elements are not covered here
See wiring for 3-phase balanced
Any 3-phase non-balanced water heater can be converted to single-phase
See 3-phase to single-phase conversion wiring

What is 3-phase
See 3-phase electric water heater service manual
Photovoltaic water heater

Electric Solar panel connected to electric water heater

Ordinary water heater elements work with DC power
Ordinary water heater thermostats will work fine with 12-48 volt DC, but will melt with high voltage DC power
Example 400 watt 24 volt DC element will raise 1.84 gallons from 60° to 120° each hour
Typical shower is 106 degrees F
240 volt DC can be connected directly to 240 V element and heat 21 gallons per hour
You can also get slower water heating using low voltage 12-24 VDC and using a single-U or double-U DC element

Buy from my associate links:
DC Element 
Single U element 
Double U element 

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Kwh needed to heat water
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Technical information
Water heater efficiency
Electric water heaters operate at 99% efficiency
Gas water heaters operate at 69% efficiency
Tankless gas heaters operate at 80% efficiency
High-efficiency tank-type gas heaters at 96% efficiency

'Efficiency' is not same as 'energy saving' .
All costs are energy: Consider total cost of water heater: Cost of unit, cost of installation, projected repairs, whether repairs are do-it-yourself, if parts are generic and available locally, true life expectancy of unit,  monthly energy bill over life of unit, and disposal-replacement cost > read more
Other factor will weigh eventually including direct carbon emissions
released at each home from gas appliances.
All costs are energy: If there was a breakthrough water heater that suddenly lowered people's bills, and reduced overall energy consumption, people would be waving their monthly bill in the air and everybody would know.  There is no news. Choose lowest overall cost water heater to save energy.
Research pdf: water-softener/water-heater efficiency comparison
Read do-it-yourself: 9 ways to save with a water heater
Effect of hard-water WITH water-softener
Efficiency of gas and electric water heaters is unchanged over time when hard water is softened, however softened water corrodes anode rod and will reduce life of water heater unless anode rod inspected and replaced every 2 years. Once anode rod is 50-75% corroded, water heater tank begins to rust. This condition leads to leaking water heater which cannot be repaired. Rusted water heaters can rupture and cause massive damage as water runs until problem is discovered.
Read more & See Anode rod options

Effect of hard-water with NO water-softener:
> Efficiency of gas heater drops 6-8% after two years > cleaning tank of sediment build-up will not restore full efficiency > however, regular flushing to prevent sediment maintains efficiency
> Tankless gas heater will fail when pressure sensor clogs with sediment within 2-3 years depending on hardness of water > regular de-liming will not restore efficiency > softener and filter are required
> Efficiency of electric heater stays at 99% until sediment reaches bottom element > cleaning tank and replacing lower element restores full efficiency > regular flushing to prevent sediment build-up also maintains efficiency
Research pdf: water-softener/water-heater efficiency comparison

Water-softener reduces life of anode rod in gas and electric water heaters
Water heater manual says: "Artificially softened water is exceedingly corrosive because the process substitutes sodium ions for magnesium and calcium ions. The use of water softener may decrease life of water heater tank."
Six-year tanks come with 1 anode rod. Read manual.
Generally, tanks with longer warranties come with 2 anode rods.
Anode rod options
Gas and electric water heaters Support the economy:
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50 gallon Gas water heaters 
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50 gallon Electric water heaters 
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