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How to figure VoltsAmpsWatts 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 208240Volt Homes in US and Americas are usually wired for 120 / 240Volt Condo buildings etc can be wired for 120 / 208Volt Ordinary water heater will work with any voltage... exception any water heater with electronic controls such as heatpump, tankless, some factorymade solar units etc that must be connected to the rated voltage and no other voltage Resources: Water heater manufacturers Find age of water heater using serial number on label Connect water heater to generator Review heat pump Review Solar water heater See inside main breaker box 

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 singlephase is household or condo electric service (Phase 3 shows on some commercial water heaters) Voltage: Label shows 208240 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 3phase nonbalanced water heater to singlephase 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 

Other
things on label Serial number/ which also contains code for date of manufacture/ Resource: Find age of water heater Gallon size of tank Number of warranty years Manufacturer and address of manufacturer/ Resource: Water heater manufacturers 

Formula for heating water inside
tank: Gallon Per Hour (Electric) = (KW x 3413) divided by (temp. rise x 8.25) or (KW x 414) divided by (temp rise.) Let's say you have 5500 watt elements. Let's say incoming water temperature is 65°F and you want to heat tank to 105°, or 40° rise in temperature. 5500 watt or 5.5Kw elements x 3413 = 18771.5 40 degree temperature rise x 8.25 = 330 So in this specific situation, each element would heat 56.88 gallons per hour If you have 4500 watt elements and incoming water temperature is 55°, and you want to heat to 120°, then the temperature rise is 65° 4.5 KW x 3413 = 15358.5 65 degree temperature rise x 8.25 = 536 So one element would heat 28 gallons per hour This number is for EACH element, but does NOT consider heat loss from tank, room temperature, or thickness of insulation etc. Remember, with residential simultaneous tank, only ONE element is ON at one time. Upper element is ON, or lower element is ON, or BOTH elements are off. At no time are both elements on. 

Larger image Volts and watts are printed on end of each element 480 volt 4000 watt or 415 volt 3000 watt When voltage drops, the element wattage also drops Typically
480 volt is common on 3phase nonbalanced commercial water heaters.
The nonbalanced 3phase heater can be converted to single phase but
attention must be paid to the element voltage and wattage
Resource: 3phase nonbalanced / and conversion to single phase 
How to figure resistive wattage by voltsOhm's laws says: Volts squared ÷ watts = ohms Resources: See chart How to test elementEach element has volt and watt rating printed on end of element If element is rated 4500 watts @ 240 volts.... then volts squared (57600) ÷ 4500 watts = 12.8 ohms So 12.8 is the ohm rating for the element, no matter what voltage is applied But what happens when voltage is reduced on the same element?? For example voltage is reduced to 208 volts instead of 240 volts. Then 208 volts squared (208v x 208v = 43264 volts˛) ÷ 12.8 ohms = 3380 watts... and the element does not burn as hot What happens when voltage is reduced to 120 volts on same element? Then 120 volts squared (120v x 120v = 14400 volts˛) ÷ 12.8 ohm = 1125 watts and heating is reduced to 1/4 the original output What happens when voltage is reduced on 480 volt, 4000 watt element? 480 Volts squared (230400) ÷ 4000 watts = 57.6 ohms/ and 57.6 is the ohm rating for element no matter what voltage. So when voltage is reduced to 415 volts: 415 volts squared (172225) ÷ 57.6 ohm = 2990 watts (or 3000 watts as shown in photo) What about increasing voltage instead of lowering voltage? What happens when 480 volts is connected to element that is rated for 4500 watts and 240 volts? POW ! element burns out 480 volts squared (230400) ÷ 12.8 ohms = 18,000 watts or 4 times the rating... and the element will butn out immediately What happens when 240 volts is connected to element that is rated for 2000 watts and 120 volt? POW again 120 Volt squared (14400) ÷ 2000 watts = 7.2 ohm 240 volts squared (43264) ÷ 7.2 ohm element = 6000 watts running through a 2000 watt element causing it to burn out So buy element that is rated for the voltage Resource: Elements and element replacement 

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 brownout when voltage drops across large area of homes. Example formula shows that wattage for 120Volts is 25% of wattage for 240Volts 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 element will raise 47 gallons water by 40 degrees in 1 hour. 1125 watts @ 120 volt heats 12 gallons water by 40 degrees in 1 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 Recovery chart 

Screwin elements 
High
and low density elements All calculations shown on this page apply to high and low density elements. Watts ÷ square inches of heating surface = density High density has less square inches of heating surface, so each square inch of element burns hotter If both elements have same watts and volts, they will still heat same amount as each other, no matter the density. All new water heaters come standard with high watt density elements Purpose of foldback type low density element: they last longer in water that has high mineral content, such as hard water Resources: How to select and replace water heater element How to test if element is working 




Larger image 
Thermostats
and elements Resources: How to wire thermostats and elements How to troubleshoot electric water heater Ready for peak electric prices? Howtowirewaterheaterwithswitchesandtimers How to wire offpeak water heater thermostats 





Use
10 gauge wire for water heaters Orangecolored 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: Yellowcolored 12 ga wire for 20 Amp breakers Whitecolored 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 

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 runtime for a water heater [depending on usage and temperature of incoming water] Bath uses 1215 Gallons hot water <> shower uses 59 Gallons hot water > Hot water use chart 5500 Watts x 3 hours = 16,500 watthours or 16.5 Kwh per day For a full 30day 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 watersoftener > 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 





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 passively preheats cold water 
Tempering
tank passively preheats 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 


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 

Water heater Box timers 

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* 100Watt 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  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 Kilowatthour? Kwh is the standard unit for billing used by electric company <=> the cost varies from 10˘  20˘ per Kwh 1 Kwh = 1000 watthours of electricity Average electric price by state 

100
Watt light
bulb turned on for 10 hours <=> 100 Watts x 10 hours =
1000 watthours or 1 Kwh 40 Watt light bulb turned on for 10 hours <=> 40 Watts x 10 hours = 400 watthours 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 

Small Refrigerator: $60 per year Big refrigerator: $300 per year 


Big Screen TV: $70140 per year Satellite receiver: $18 per year TV: 300500 Watts + 3 watt standby $.10 per Kwh 6 hours TV per day = $70140 per year 
Look at appliance label
> each appliance has Watt rating For example doubleoven 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 $26 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 
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Electrical pagesHow to wire arc fault breaker How to wire GFCI How to wire GFCI combo Basic water heater circuit How to wire water heater for 120Volt Install old work box How to drop wire from attic Wire connector How to wire 240volt outlets How to install 3phase timer How to wire 3phase outlets How to wire 3phase surge protector What is 3phase How to wire whole house surge protector How to wire undercounter water heater See inside main breaker box Replace breaker Install subpanel Fuseholder Contactors How to solder wires Whole house surge protector 3phase surge protection Circuit breakers Difference between 120 volt and 240 Volt Difference between 50Hz and 60Hz How to install electric meter on water heater How to wire water heater thermostat How to wire water heater with switches and timers 6x6x4 Enclosures Intermatic timer enclosures Read how to convert AC water heater to DC/ high voltage Convert AC water heater to DC/ low voltage How to wire DC solar water heater DC relays for solar water heater How to add another thermostat to water heater How many Kwh to heat water Chart for figuring heating time for electric heater 
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