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How to figure Volts-Amps-Watts for residential water heater |
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Find
label on side of water heater Take photo of label for records. Water heaters with 2 elements are rated 208-240Volt Homes in US and Americas are usually wired for 120 / 240Volt Condo buildings, apartments can be wired for 120 / 208Volt Commercial buildings have variety of voltages including 120/208/240/277 Ordinary water heater will work with any voltage, up to 480 as long as voltage does not exceed element rating... exception water heater with electronic controls such as heat-pump, tankless, some factory-made solar units etc that must be connected to the rated voltage and no other voltage Resource: Connect water heater to generator Review heat pump Review Solar glycol water heater See inside main breaker box High voltage solar PV Low voltage solar PV Commercial 3-phase water heater |
 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, which can be converted to single-phase. Resource: Commercial 3-phase water heater 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 is 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 Resource: 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 What is 208 volt |
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Different
water heater label/ 4500 watts @ 240volts Label shows 4500 watt elements @240Volt Total connected 4500 watts, which means both elements are never ON at same time so the maximum wattage consumed by this water heater is 4500 watts. Homes, houses, and many ordinary apartment buildings have 240Volts While apartment and condo buildings might 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 Resource: How electric water heaters work |
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Other
things on label Serial number/ which contains code for date of manufacture/ Gallon size of tank Manufacturer brand Number of warranty years. Warranty is usually from date of purchase. Lacking sales receipt, the warranty reverts to date of manufacture, which might be several years before purchase. Warranty usually covers tank + parts + labor first year, then tank + parts following years. Resource: Find age of water heater 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. |
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Test element:
Remove wires from element. Set multimeter to
read continuity or ohms. Resource:
How to test elements -Element can be partially shorted from melted sections of the resistance wire inside element, and draw more amps than expected... you should be able to see this by measuring ohms across both screws .... replace element. -Element can be shorted to ground and cause overheat water heater in some cases, and this can be determined by testing either screw terminal to steel tank.... replace element. -Element can be shorted out ... measuring ohms across both screws and get 1 or 0 ohms of ... replace element. Buy: Multimeter  Resource: Element replacement |
 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 3-phase non-balanced commercial water heaters.
The non-balanced 3-phase heater can be converted to single phase but
attention must be paid to the element voltage and wattage
Resource: 3-phase non-balanced / and conversion to single phase |
How to
figure resistive wattage by volts Ohm's laws says: Volts squared ÷ watts = ohms NOTE: The following numbers are based on 'cold resistance.' Ohms is a measure of resistance and heat affects resistance, so if you test element inside a heated tank, the ohm rating will be different. For example 3500W /240V element can vary from 16Ώ hot to 10Ώ cold. Resource: See chart How to test element Remove wires from element to test. Set multimeter to read ohms Ώ. Each 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 burn 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 Always buy element that is rated for the voltage Resource: Elements and element replacement |
 Both elements in example are 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  Save during peak electric pricing by converting water heater to 120V. Not recommended for ordinary usage. Only for peak hours. Connect water heater to generator and have some hot water during power outage. Lower wattage heats more slowly. If elements is rated for 4500 watts @ 240Volt ....and you apply 240volt, you get 4500 watts = raises 47 gallons water by 40 degrees in 1 hour. ....or you apply 120volt, and get 1125 watts = raises 12 gallons water by 40 degrees in 1 hour. Tank stays hot with 120 volt, but amount declines rapidly when hot is used, and reheat is slower. With 120 volt, the electric consumption is spread across more hours. It still takes same amount of energy to heat a gallon water, so cost per heated gallon stays same. Resource: How to convert water heater to 120Volts Connect water heater to generator Recovery chart Figure Kwh needed to heat water |
  Screw-in 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. Low density has more square inches of heating surface, so each square inch burns cooler. If both elements are rated 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. Rule of thumb: if elements burn out frequently, change to low watt density. Help prevent burn-out by draining tank periodically and cleaning sediment build up in water heater. Resource: How to select and replace water heater element How to test if element is working |
  Thermostats are generic: Substitute Apcom with Therm-o-disc or Apcom or 89T etc Make sure upper thermostat has 3 screws on right side for 2-element tank Temperature range 90-150° Therm-o-disc/ reset trip @ 170° Temperature range 110-160° Apcom/ reset trip @ 180° Local YMCA hot tub = temperature 105°/... Typical shower-bath = 110°F Residential water heater TP valve will release water at 170° Read more about thermostats |
Thermostats
are rated for any voltage Thermostats will work with 12-24-36-48 volt AC DC 120-208-240-277-380-415-440 Volt AC up to 480 volt High voltage DC from direct wire to solar panels will melt thermostats. Resource: for Solar PV water heater: Convert water heater to high voltage DC Convert water heater to low voltage DC How to set up solar array Thermostats are mechanical bi-metal switches and do not depend on voltage to work. Thermostat must sit flat aginst tank and be covered with insulation, or they will mistead tank temperature. Thermostats temperatures are approximatly, and vary by calibration. Residential thermostats are rated 90-160° F/ with reset trip out at 170°F Commercial thermostats are rated 120-180 ° F/ with reset trip out at 200° F Do NOT use commercial thermostats on residential water heater. Cautions: Danger of severe burns with water exceeding 135° F... apply cold water to burns... call for medical help. Electrical burns are different: do not apply water. Elderly people are often not able to feel or respond to hot water ... adjust temperature on water heater to 105-110° F for elderly people... typical hot tub temperature might be 113°F and there is usually a time limit and advisory against folks with breathing problems sitting in hot tub. Do not work on live eletricity while wearing oxygen. Oxygen is flammable and can be ignited from electric spark. Make sure power is off. Buy 90-150 degree F for residential tank: Water heater thermostats at Amazon Rheem thermostats More thermostats 89T short/ dual-element thermostat at Amazon All therm-o-disc products Resource: Select and replace thermostats 120-180° Commercial and 3 phase thermostats How to wire thermostats Add another thermostat to gas or electric water heater Troubleshoot electric water heater Difference between Rheem thermostats |
 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 instead of 120 volts, then wattage is reduced:: (80 ÷ 120) squared = 44% ... so 40 watt bulb rating is reduced to 40 watt x .44 = 17.6 watts Resource: Choose correct wire and breaker size Avoid equipment damage from brownout using compressor defender |
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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. Resource: Select wire and breaker size How to replace element How to test element |
 Wire size and breaker must match Use 10 gauge wire with 30 amp 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 Using oversized breaker and wire will run cooler, and breaker box and breaker will last longer Consider 30 amp breaker: safe maximum is 80% rated valve: or 30 amps x .8 = 24 amps So safe maximum for 30 amp breaker and 10 gauge wire is 24 amps... NOT 30 amps How many watts? 24 amp safe maximum x 240 volts = 5760 watts (amps x volts = watts) Resource: Select wire and breaker size How to replace circuit breaker Troubleshoot: water heater is blowing breaker |
 Wire size and breaker must match Use 12 gauge wire with 20 amp 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 Using oversized breaker and wire will run cooler, and breaker box and breaker will last longer Consider 20 amp breaker: safe maximum is 80% rated valve: or 20 amps x .8 = 16 amps So safe maximum for 20 amp breaker and 12 gauge wire is 16 amps... NOT 20 amps How many watts? 16 amp safe maximum x 240 volts = 3840 watts (amps x volts = watts) If 20 amp breaker is rated for maximum 3840 watts, then it is too small for 4500 watt water heater Replace 4500 watt elements with 3500 watt elements/ heating will be slower, but will get the job done Resource: Select wire and breaker size How to replace circuit breaker Troubleshoot: water heater is blowing breaker |
 Breaker switches must be connected by a bar so both switches operate as one switch |
Circuit
breaker resources: Circuit breakers
respond to heat on wire. When a short circuit occurs, too much
electricity begins to flow through wire, causing wire to get hot and
tripping breaker. Wire size and breaker amp rating must match for the
breaker to work properly. Figure correct wire and breaker Water heater is tripping breaker How to replace circuit breaker How to wire gfci Difference between gfci circuit breaker and ground Why you need ground wire Can AC breaker be used for DC breaker How to reset circuit breaker Not enough space for circuit breakers Circuit breakers How to install subpanel Match breaker and wire size How to wire subpanel See inside breaker box How to wire safety switch How to wire whole house surge protector Figure volts amps and watts Main breaker stress test |
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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 Resource: Select correct wire and breaker size |
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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 all 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 |
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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 5500-6000 Watt element since they heat more water. Most residential tanks have 4500 Watt elements Small 4-20 gallon under-counter water heaters have elements rated for 120 volt and 1500 watt If elements burn out frequently, reduce element wattage, or install low density element. Resource: How to select and replace element |
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Avoid
damage from surge: Most ordinary electric water heaters are not damaged by surge. Exception, water heaters with electronics. However, powerful lightning strike can damage any water heater, especially modern electronic water heating equipment and other appliances. Lightning strike will energize nearby wires, causing power surge. Simple power outage can also cause power spikes when power is restored Install surge protection at the breaker panel or at the location of equipment Surge protectors are single-use. Over time, all surge protectors wear out because of constant variations in electric power coming over the grid. Resource: Read about Type 1 and Type 2 surge |
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Household
water heaters are wired for NON-simultaneous operation. Both elements are not ON at same time Resource: How to wire water heater thermostats How water heaters work How to wire off-peak water heater |
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Thermostats
and elements Resource: How to wire thermostats and elements How to troubleshoot electric water heater Resource: How-to-wire-water-heater-with-switches-and-timers How to wire off-peak water heater thermostats |
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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 |
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 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 |
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Cost to operate water heater How much does it cost to operate gas and electric water heaters |
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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 |
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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 |
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| 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 |
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 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 Resource: Add a tempering tank to preheat very cold incoming water 9 ways to save with water heater |
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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 contactor Resource: 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 |
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 Water heater Box timers |
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   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 |
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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 |
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AMPS
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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 amperage |
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 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 |
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| 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 |
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 Small Refrigerator: $60 per year Big refrigerator: $300 per year |
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 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 |
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