2. -or- Find owners manual -or- Google brand and model number of heater to find .pdf of manual
3. Voltage & wattage also written on end of each element see example
See larger image
1. Capacity of tank (80, 50, 40, 30, 20 gallons etc)
2. Voltage (120, 209, 240) <=> in US, 120 & 240 Volts is standard
3. Element wattage from 600 to 6000
1. Voltage of water heater appliance is usually 120 Volts or 240 Volts
2. Watt rating of element(s) is usually 1500, 3500, 4500, or 5500 Watts
Volts x Amps = Watts --which is the same as-- Amps = Watts ÷ Volts
V x A = W
A = W ÷ V
The water heater label gives you Volts and Watts
5500 Watt element ÷ 240 Volts = 22.91 Amps or 23 Amps
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
Watt rating for tank equals element Wattage
So, if water heater has 2 elements and both elements are 5500, then overall tank Wattage is 5500
+++ This is because both elements are never turned on at same time see example on label
Read how water heater thermostats work- technical
For safety > a circuit breaker is allowed to handle 80% of Amps shown
30 Amp circuit breaker x .80 = 24 Amps maximum
20 Amp circuit breaker x .80 = 16 Amps max
15 Amp circuit breaker x .80 = 12 Amps max
And we calculated that a 30 Amp circuit breaker can carry 24 Amps
So a 30 Amp circuit breaker can safely handle the 23 Amps needed for a 5500 Watt water heater
Oversized breaker and wire run cooler and save money, but make sure breaker size and wire size match
Orange-colored 10 gauge wire for 30 Amp breakers
Yellow-colored 12 ga wire for 20 Amp breakers
White-colored 14 ga wire for 15 Amp breakers
18 ga lamp cord is for 1 residential can opener, pencil sharpener, floor lamp etc
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 Read research pdf
5500 Watt tank = $49.50 per month + tax
4500 Watt tank = $40.50 per month
3500 Watt tank = $31.50 per month assuming low usage
1500 Watt tank = $13.50 per month
5500 Watt tank = $59.40 per month + tax
4500 Watt tank = $48.60 per month
3500 Watt tank = $37.80 per month assuming low usage
1500 Watt tank = $16.20 per month
Read 9 ways to save with a water heater
How-to-wire-water-heater-with-switches-and-timers
How to wire water heater thermostats
How to wire off-peak water heater thermostats
Ordinary wall timers are usually 15 Amps [unless rated for heavy duty]
Ordinary household light switch is usually 15 Amps
Lowes carries Cooper-brand green-color 30 Amp switch
Again the 80% safety rule applies, so .80 x 15 Amp = 12 amps maximum for a 15 amp switch or timer
When wired to a water heater contactor, ordinary switches can control a water heater
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
Simply add up the Watts of each item to calculate the total load on the switch.
The 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 <> this is why it is important to learn the basics about electricity >>> see Electricity from power pole to breaker box
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 4500 Watt element gets hotter than 3500 Watt element, and 4500 Watt uses more total energy
Larger water heaters hold more water so they use higher Wattage elements
Think about a light bulb. A closet can be lit with one 40 Watt bulb. But a large room requires more Wattage.
So large water heaters use a 5500 Watt element since they heat more water than small tanks
What is the difference between 120 and 240 Volts?
The circuits are wired differently: 120 Volt circuit has 1 hot wire, while 240 Volt circuit has 2 hot wires
240 Volt circuits deliver more energy
It turns out that 240 Volts can deliver energy more efficiently than 120 Volts.
So 240 Volt appliances are more efficient.
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
The roadway is made up of the circuit breaker, wire, and electrical connectors needed to handle the energy
See inside main breaker box
Kwh is the standard unit for billing used by electric company <=> the cost varies from 10¢ - 14¢ per Kwh
1 Kwh = 1000 watt-hours of electricity
Figure a 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 $.10 per Kwh = .04 or just 4¢ for each 10 hours of 60 Watt light
with 6.5 Amp/ full load
115 Volt/
786 Watt/
... uses about 1.6 Kwh per day or 600 Kwh per year.
@$.10 per Kwh = $60 per year
@$.12 per Kwh = $72 per year
Big Screen TV: 300-500 Watts
+ 3 watt standby
Costs 3-6¢ per hour to watch TV..
6 hours per day = $70-140 per year
For example a 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 takes same energy to heat water and heat homes and cook food as before. A giant appliance does not give you 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. Read tips from TVA. 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.
Remember, when everybody conserves electricity, the price remains low and fewer resources are used
