# High Electricity Bills? These Appliances Are the Most Expensive to Run

Eugene is a qualified control/instrumentation engineer Bsc (Eng) and has worked as a developer of electronics & software for SCADA systems.

## How Much Does Electricity Cost?

With the cost of electricity rising all the time, it is nice to know how the various electrical appliances in the home are contributing to the cost of your electricity bill.

In this short article, I try to give a comprehensive list of appliances and an estimate of the cost of running them. The power used by an appliance can differ somewhat from the values quoted but these are typical values. The cost per hour is based on a price of 15c per unit, but you can scale up depending on what your electricity supply company charges you.

What is Electricity? Understanding Volts, Amps, Watts, Ohms, AC and DC

## Example

To work out the cost of running an appliance, we use this equation:

Cost = (Power in watts / 1000) x (cost per unit in cents) x time in hours

E.g. An electric heater with a 2000-watt rating is switched on for 2 hours. If electricity costs 10 c per unit, how much does it cost to power the appliance for this period?

Power in watts = 2000

Cost per unit = 15

Time in hours = 2

Cost = (Power in watts / 1000) x (cost per unit in cents) x time in hours

= (2000 / 1000) x 15 x 2 = 60 cents

The heater is rated at 2000 watts. This means it uses 2000/1000 = 2 units or kilowatt hours (kwh) in 1 hour. If it was switched on for 15 minutes, it would have used 2000/1000 x 0.25 = 1/2 a kWh. So basically you just need to work out the power in kilowatts by dividing the power in watts by 1000 and then multiply the result by the number of hours followed by the the cost per kWh in cents (or whatever your local currency is)

## What is a Kilowatt Hour Meter or Electricity Meter?

The utility company that supplies you with electricity keeps track of your energy usage using a kilowatt hour meter, fitted inside your home or on the wall outside. This meter measures voltage, current and time and displays the result in units or kWh on a mechanical counter display. Newer meters are replacing the older electromechanical types and have electronic displays that plus they can also be read wirelessly.

## How Do I Know the Wattage of an Appliance?

The voltage, wattage and possibly the current will be specified on the appliance. This information may be embossed into the casing or printed on a label/metal panel. Sometimes this label is located at the back of the appliance e.g. on TVs, washing machines, freezers or other white goods. On kettles, food processors, etc, this information may be printed on the underside.

## Which Appliances Use The Most Power?

Air conditioning, electric showers, clothes driers (tumble driers), room heaters and water heaters (immersion heaters) are the most energy hungry appliances. Kettles are also high powered appliances, however since they are turned on for a relatively short period of time, the overall energy cost isn't too high.

## The Most Common Appliances in the Home and the Cost of Running Them (Assuming Electricity is 15c per Unit)

AppliancePower in wattCost per hour in centsNotes on cost

Kitchen range/cooker

2000 to 6000

30 to 90

Depending on number of hotplates and whether oven is switched on

Tumble drier

2500

37

Washing machine

1000 on average

15

Fridge

60

0.45

Depends on ambient temperature

Freezer

80

0.6

Depends on ambient temperature and capacity of freezer

Kettle

2000 to 3000

30 to 45

Food processor

500 to 1500

7.5 to 22.5

Laptop

25

0.38

Desktop computer

100

1.5

Cost is less with LCD monitor

Large TV CRT

100 to 150

1.5

Large TV Plasma

200 to 300

3 to 4.5

Large TV LCD

100 to 200

1.5 to 3

Large TV LED

80

1.2

Alarm system

20

0.3

HiFi

30

0.45

4

0.06

Hair drier

1500

23

Microwave oven

1200

18

Air conditioning

5000

75

Depends on temperature setting on unit

14

0.22

100 watt light bulb

100

1.5

Cordless phone

<1w

0.01

Computer printer

12

0.18

Toaster

1000

15

Water tank heater

3000

45

Electric shower

7000 to 10000

105 to 150

Phone charger

5 to 10 W

7.5 to 15

## What is Vampire Power or Phantom Power?

Many devices draw so called vampire power when on standby. These include sound systems, TVs, HiFis, video and DVD players/recorders, Computers, radios etc. Power drawn on standby can be up to 25% of that when fully turned on. If you want to save money - pull the plug.

## What is a Power Consumption Monitor?

A power monitor is a useful device for tracking electricity usage and helping you save energy. The monitor is plugged into a wall socket and then the appliance is plugged into the adapter. The device then displays power consumption in watts and tracks energy use in kWh over time. It can also display voltage, current and length of time the appliance is powered on. This is useful for checking the duty cycle or percentage on time for devices that cycle on and off (e.g. fridges, freezers and air conditioners). You can read more about them in this guide:

Checking Power Consumption of Appliances With an Energy Monitoring Adapter

The Kill a Watt energy usage monitor from Amazon is a basic unit that monitors voltage, amps, watts, kWh and time run. It's easy to use and each parameter can be selected by simply pressing a dedicated button. Values are displayed on a clear easy-to-read LCD display. Note that this is designed for AC 115 volt appliances.

Question: How much wattage or power has my e-bike charger consumed in 9 hours? The input specifications are: Ac 180 to 260 V & 4 Amp. Max. The output specifications are: 54.6V & 6Amp. My e-bike battery is 48v, 24 Ah.

Answer: It depends on your supply voltage and the actual current drawn by the charger, but this will vary during the charging process.

So let's assume the voltage is 230 volts, and current is maximum, i.e. 4 amps.

Then max power input is 230 x 4 = 920 W

Max energy consumption is (230 x 4 /1000) x 9 = 8.28 kWh or units.

However, if the batteries are lithium ion, charging current varies, and a multi-stage charger will charge at a constant current during the first stage until the voltage reaches a certain level. Then the current decreases as the charger puts out a constant voltage during the second stage of charging. So actual energy use will be less than this, maybe half.

Energy = Power x time, so for a constant load e.g. a heater you simply multiply the power by time to get a figure for energy consumption. For a device like the charger above where the power varies, the best way to measure actual energy consumption is to use a power/energy adaptor which will give a more accurate figure as it continually measures instantaneous power and does an integration calculation and comes up with a total figure for energy use.

Eugene Brennan (author) from Ireland on February 23, 2020:

Hi khtanned,

This is a B&Q brand power adapter, so only available in the UK and Ireland.What style of plug (country) do you need on the meter?

khtanned on February 22, 2020:

I would like to get this power meter. May I know the brand or manufacturer.

Thanks

K N S Prasad on December 26, 2017:

Very nice for explaining thanks so much.

Delores Wiley on March 13, 2017:

thank you very much I could not read a lot of my appliance wattage and this is very helpful