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2014

How to figure Volts-Amps-Watts for residential water heater

1. Find label on side of water heater
Take photo of label for records.
Water heaters with 2 elements are rated 208-240Volt
Homes are usually wired 240Volt
Condo buildings etc can be wired for 208Volt
Water heater work with any voltage

Resources:
Water heater manufacturers
Find age of water heater using serial number on label

Connect water heater to generator

Water heater label
Typical electric water heater label
See larger image
See another image
Look for Volts and Watts on label
Always test volts first, and then look for watts

Label shows Phase: Phase 1 or single-phase is household or condo electric service (Phase 3 shows on some commercial water heaters)
Voltage: Label shows 208-240 Volts since these are typical voltages
Each element is 5500 watts: Label shows Two 5500 Watt elements @240V
Each element is rated 4125 watts when connected to 208V instead of 240V
Total connected 5500 watts means both elements are never ON at same time.

Note about 208Volt: 5500 Watt rating drops to 4125 watts when tank wired to 208V.  Why? Water heater elements are like light bulbs... When power drops, then light bulbs dim, and produces less wattage output. Same with elements: when voltage drops, the element is less hot and wattage output is lower

Resources: Tank wiring can be changed: 
How to wire thermostats and elements

Off peak water heater wiring
Convert 3-phase non-balanced water heater to single-phase
How electric water heaters work

See larger image
Different water heater label/ 4500 watts @ 240volts

Label shows 4500 watt elements @240Volt

Total connected 4500 watts, which means both elements are not ON at same time.
Homes, houses, and many ordinary apartment buildings have 240Volts
While many apartment and condo buildings have 208Volt service

Note: 4500 watt element @ 240V changes to 3375 watt element @ 208 volts
Watt rating drops when voltage drops
Always test voltage first before figuring watts


Element rated for 4500 watts @ 240Volt
Reducing voltage reduces wattage
Resistive loads like water heater elements, watt consumption drops when voltage drops.
For example light bulb gets dim in a brown-out when voltage drops across large area of homes.

Example formula shows that wattage for 120Volts is 25% of wattage for 240Volts

wattage formula

Save water heater costs during peak electric pricing by converting water heater to 120V. Not recommended for ordinary household usage. Only for peak hours.
Lower wattage heats more slowly.
4500 watt @ 240 volt heats 21 gallons per hour
1125 watts @ 120 volt heats 5 gallons per hour. Tank stays hot.
Electric consumption spreads across more hours. It still takes same amount of energy to heat water, so cost per
heated gallon stays same.
Resource:
How to convert water heater to 120Volts

Formulas:
Volt x Amp = Watt

Amp = Watt Volt

More Electrical formulas
Water heater label shows Volts and Watts
Volts x Amps = Watts         --Same as--      Amps = Watts Volts


Calculate amp size of breaker using formula:
5500 Watt element  240 Volts = 22.91 Amps or 23 Amps

Other examples
4500 Watt element  240 Volts = 18.75 Amps
3500 Watt element  240 Volts = 14.5 Amps
1500 Watt element  240 Volts = 6.25 Amps
  
40 Watt light bulb  120 Volts =  0.33 Amps
If resistive load, such as light bulb or water heater element,  receives less voltage, then the watt rating is less.
If 40 watt light bulb receives 80 volts, then wattage is reduced::
(80   120) squared = 44% ... so 40 watt bulb rating is reduced to 40 x .44 =  17.6 watts
Resource:
Choose correct wire and breaker size
Water heater element
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Volts and watts show on end of element

When replacing elements, use same Wattage shown on tank label
Any generic element will work as replacement
If using smaller wattage, tank will heat slower.

Tank warranty is voided when installing higher wattage element than shows on label
And this can be dangerous if wire size and breaker do not match load. Best to match element rating with tank label. Generic hardware store elements are good choice. Expensive 'lifetime' or 'extended warranty' elements are probably money-wasteful for homeowner.
Resources:
Select wire and breaker size
How to replace element
How to test element
water heater circuit breaker 10 gauge wire and 30 amp breaker
for 4500 watt and 5500 watt elements @ 240Volts


5500 Watt element  240 Volts = 22.91 Amps or 23 Amps
4500 Watt element  240 Volts = 18.75 Amps
Oversized breaker and wire will run cooler, and breaker box and breaker willl last longer

Resources:
Select wire and breaker size
How to replace circuit breaker
Troubleshoot: water heater is blowing breaker
12 gauge wire and 20 amp breaker
for 3800 watt and 1500 watt elements @ 240Volts


3500 Watt element  240 Volts = 14.5 Amps
1500 Watt element  240 Volts = 6.25 Amps

Resources:
Select wire and breaker size
How to replace circuit breaker
Troubleshoot: water heater is blowing breaker
wire and breaker size chart
Larger image
Wire and breaker chart

For ordinary residential non-simultaneous water heater
Test voltage
Identify element wattage
Look for total connected watts on label
Use chart to find correct wire and breaker


Resources:
Select wire and breaker size
What does Watt rating mean?
Think about the difference between 40 Watt and 100 Watt light bulb.
Higher the Watts, the hotter the light bulb, and the higher output of total energy
So 5500 Watt element gets hotter than 3500 Watt element, and 5500 Watt uses more total energy


Why are elements different Wattage?
Think about a light bulb. A closet can be lit with one 40 Watt bulb. But a large room requires more Wattage.
So very large water heaters use 5500 Watt element since they heat more water.
Most residential tanks have 4500 Watt elements

If elements burn out frequently, reduce element wattage, or install lower density element.
Resources:
How to select and replace element
No image available
AO Smith

Resources:
Sears Kenmore (AO Smith) sell sheet/ requires 30 amp breaker and 10 gauge wire
How to adjust water heater temperature
9-ways to save with water heater
How to wire thermostats and elements
Off peak water heater wiring
How to replace elements
Smaller wattage on lower element? Probably does not save much.
DualWatt™ Lower element:

Choose between 3800 watt and 5500 watt connection on lower element.
Upper element remains 5500 watt.
Does smaller wattage on lower element save money? Probably not.
Why? because it takes same number of Kwh to heat gallon of water, no matter which size element. All cold water entering tank must be heated to thermostat set point
Exceptions where DualWatt element might save money:
1) Tanks wired for Off-peak, but then any element will achieve same result
2) States that have peak electric pricing, the lower wattage will reduce consumption a bit by heating water more slowly, thus spreading electric usage over more time.
3) Lower wattage elements generally lasts longer and do not burn out as frequently as higher wattage elements. Or replace element with low density element.
4) Replace upper element with 3800 watt, and set lower element to 3500 watt, and you can use 12 gauge wire and 20 amp breaker without upgrading electric to 30 amp breaker and 10 gauge wire
Turning down temperatyure on lower element is better strategy for saving.

Larger image
Thermostats and elements

Resources:
How to wire thermostats and elements
How to troubleshoot electric water heater

Ready for peak electric prices?
How-to-wire-water-heater-with-switches-and-timers
How to wire off-peak water heater thermostats
electric water heater Household water heaters are wired for NON-simultaneous operation.

Both elements are not ON at same time

Resources:
How to wire water heater thermostats
How water heaters work
How to wire off-peak water heater
240 volt water heater circuit Basic 240Volt water heater circuit

Example shows water heater on dedicated 240Volt breaker.

Dedicated means the breaker does not supply power to other circuits.
Another example: Microwave oven is normally on dedicated 120Volt breaker

Resources:
How to replace circuit breaker
How to install subpanel
Troubleshoot electric water heater
Install electric meter on water heater
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Electric meter on water heater

How to install electric meter on water heater
color-code household wire

Use 10 gauge wire for water heaters

Orange-colored 10 gauge wire for 30 Amp breakers
30 Amp breaker x 240Volts = 7200 watts  => 80% rule applies: 7200 Watts x 80% = 5760 Watts safe maximum
          80% rules applies to household electrical loads

Other ratings:
Yellow-colored 12 ga wire for 20 Amp breakers
White-colored 14 ga wire for 15 Amp breakers
18 ga lamp cord or 1 residential can opener, pencil sharpener, floor lamp etc
Resource:
Ratings and color code for wire

What size circuit breaker? 30 Amp
For safety > a circuit breaker is allowed to handle 80% of Amps shown
Water heater safety: always use 10 gauge wire and 30 amp breaker
30 Amp breaker x 80% rule = 24 Amps safe maximum

Calculation above shows that 5500 Watt water heater uses 23 Amps
And 30 Amp circuit breaker can carry 24 Amps
So a 30 Amp circuit breaker can safely handle the 23 Amps needed for 5500 Watt water heater

Oversized breaker and wire run cooler and save money, but make sure breaker size and wire size match
Resource:
Ratings for breaker and wire

Cost to operate water heater
How much does it cost to operate gas and electric water heaters


Small water heater


Avg electric price by state
Avg state price chart in pdf

How much does it cost to run Electric water heater:
3 hours is approximate daily run-time for a water heater [depending on usage and temperature of incoming water]
Bath uses 12-15 Gallons hot water <> shower uses 5-9 Gallons hot water > Hot water use chart

5500 Watts x 3 hours = 16,500 watt-hours or 16.5 Kwh per day
For a full 30-day month <=> 30 days x 16.5 Kwh per day = 495 Kwh per month for water heater electricity
Calculate cost <=> 495 Kwh x $.10 per Kwh = $49.50 + tax
As general rule, electric water heaters operate at 99% efficiency with or without water-softener > until sediment reaches bottom element > full efficiency is restored when sediment removed How to remove sediment   Read research pdf
3 hours a day @ $.10 per Kwh
5500 Watt tank = 495 Kwh per month  = $49.50 per month + tax
4500 Watt tank = 405 Kwh per month  = $40.50 per month
3500 Watt tank = 315 Kwh per month  = $31.50 per month assuming low usage
1500 Watt tank = 135 Kwh per month  = $13.50 per month

     3 hours a day @ $.12 per Kwh
    5500 Watt tank = $59.40 per month + tax
    4500 Watt tank = $48.60 per month
    3500 Watt tank = $37.80 per month
    1500 Watt tank = $16.20 per month
     3 hours a day @ $.14 per Kwh
    5500 Watt tank = $69.30 per month + tax
    4500 Watt tank = $56.70 per month
    3500 Watt tank = $44.10 per month
    1500 Watt tank = $18.90 per month
     3 hours a day @ $.16 per Kwh
    5500 Watt tank = $79.20 per month + tax
    4500 Watt tank = $64.80 per month
    3500 Watt tank = $50.40 per month
    1500 Watt tank = $21.60 per month
     3 hours a day @ $.20 per Kwh
    5500 Watt tank = $99.00 per month + tax
    4500 Watt tank = $81.00 per month
    3500 Watt tank = $63.00 per month
    1500 Watt tank = $27.00 per month
Chart  above in pdf

Smaller water heaters are cheaper to run if family can conserve Size chart
Read 9 ways to save with a water heater
Compare 13 electric water heater timers
Electric water heaters operate at 99% efficiency with or without water softener Read
Tempering tank
Tempering tank passively pre-heats cold water
Tempering tank passively pre-heats cold water

Incoming water to household is geothermally heated since pipes are underground

Resources:
Add a tempering tank to preheat very cold incoming water
9 ways to save with water heater
Amp rating for switches

Control water heater with Switches and Timers
The 80% safety rule applies to 15 amp switches and timers, so .80 x 15 Amp = 12 amps maximum
So switch and timer have to be wired to a contasctor

Resources:
How to install 15 amp wall timer to control water heater
Control water heater with phone
Control water heater with switches
Ordinary switches can control a water heater
Water heater timers
Compare timers
Water heater Box timers
    Light bulb
15Amp switch  is rated for 1440 Watt
14 - 100Watt light bulbs = 1400Watts
How many light bulbs can 15 Amp light switch safely handle: 14 100watt light bulbs
15 Amp switch x .80 = 12 Amps
12 Amps x 120 Volts = 1440 Watts, therefore *14*  100-Watt light bulbs can be put on a single 15 Amp switch



Ordinary house switch can safely control several light bulbs + a desk lamp + a ceiling fan + etc. up to 1400 Watts
Add up Watts of each item to calculate the total load on the switch.
Same facts hold true for wall plugs which are usually rated 15 Amps and can carry 1400 Watts.

You can see that 1500 Watt microwaves and 1500 Watt space heaters should connect to heavy wires and switches

Resource:
Electricity from power pole to breaker box

Difference between 120 and 240 Volts

All single phase circuits require 2 wires to complete the circuit
    120Volt take 1 hot wire and 1 neutral wire
    240Volt takes 2 hot wires
    No neutral wire is needed to complete 240Volt circuit

240 Volts can deliver energy more efficiently than 120 Volts
240 Volt appliances are more efficient

Resource:
See basic 120 & 240 water heater circuit
AMPS   Highway Information about Amps:
Amps is a measure of the size roadway needed to supply energy to appliance
For example, a 5500 Watt element needs more roadway than a 40 Watt light bulb
Roadway is made up of circuit breaker, wire, and electrical connectors needed to handle the energy

See inside main breaker box
What is Kwh or Kilowatt-hour?
Kwh is the standard unit for billing used by electric company <=> the cost varies from 10 - 20 per Kwh
1 Kwh = 1000 watt-hours of electricity Average electric price by state
100 Watt light bulb turned on for 10 hours <=> 100 Watts x 10 hours = 1000 watt-hours or 1 Kwh
40 Watt light bulb turned on for 10 hours <=> 40 Watts x 10 hours = 400 watt-hours or .4 Kwh
To calculate cost, multiply Kwh x price <=>
For example .4 Kwh x  $.10 per Kwh = .04 or just 4 for each 10 hours of 60 Watt light
appliance watts
small refrigerator
Small Refrigerator: $60 per year
Big refrigerator: $300 per year
Small 786 watt Refrigerator rated 6.5 Amp/ full load      
115 Volt

1.6 Kwh per day = 600 Kwh per year.
@$.10 per Kwh = $60 per year
@$.12 per Kwh = $72 per year

Buy:
Refrigerators at Amazon
Watt meters at Amazon
Big screen TVs at Amazon

Kill a watt meter
Use Kill A Watt meter to measure 120Volt electric usage
Resource:
Kill a watt instruction .pdf
Big screen TV
Big Screen TV: $70-140 per year
Satellite receiver: $18 per year

TV: 300-500 Watts + 3 watt standby
$.10 per Kwh
6 hours TV per day = $70-140 per year
Look at appliance label > each appliance has Watt rating
For example double-oven has a Watt rating of 7.0 KW - that means 7000 Watts
The top oven uses 1/2 total wattage or 3500 watts or 3.5 KW >> the bottom oven uses 1/2 or 3.5 KW
For every hour the top oven is 'on' uses up to 3.5 Kwh of power
When both top and bottom ovens are 'on' for one hour, the appliance uses up to 7.0 Kwh

When buying appliance:
Look at wattage printed on label. Take photo of label with phone. Compare wattage with old appliance. It requires same energy to heat water and heat homes and cook food as before. A giant appliance does not lower bills. Energy Star rating does NOT mean new appliance will pay for itself. With Energy Star, expect $2-6 per year on same size appliance. Appliances give off warm air that works against AC in summer, but helps heater in winter. Reducing consumption and buying smaller wattage appliance is best way to lower energy bill.

Put your TV and satellite box and computer on a power strip/ turn off power strip when not in use
Resource:
Look at power strips that have timers.
Put bath fan, garage light and whole house fan on a countdown timer.

Read more about standby power loss Read1 Read2
Remember, when everybody conserves electricity, the price remains low and fewer resources are used

Additional Links

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Electricity from pole to breaker box

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9+ ways to save with water heater

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How to install subpanel

How to wire off-peak water heater

Cost to operate gas and electric water heaters

Compare all water heater timers

Anode rods

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Clean sediment from tank
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Hot water circulation system
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How to wire 240Volt plugs and outlets

How to wire switches and plugs

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Gas and electric water heaters 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
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