Units of Electricity
One of the most common units of electrical power for appliances is the watt (W). Other common units of power include kilowatts (kW), British thermal units (BTU), horsepower (hp), and tons.
Watts, Kilowatts, and Kilowatt-Hours
Watts (W) is a unit of power used to quantify the rate of energy transfer. It is defined as 1 joule per second. A kilowatt is a multiple of a watt. One kilowatt (kW) is equal to 1,000 watts. Both watts and kilowatts are SI units of power and are the most common units of power used.
Kilowatt-hours (kWh) are a unit of energy. One kilowatt-hour is equal to the energy used to maintain one kilowatt of power for one hour. Generally, when discussing the cost of electricity, we talk in terms of energy. Energy (E) and power (P) are related to each other through time (t):
E = P × t
Electricity is most often measured and paid for based on the number of kilowatt-hours used. The reason that kilowatts-hours are typically used as a measurement of energy rather than watt-hours is simply because of scale: the amount of energy a typical household uses in a year is on the order of millions of watts, so it is easier to discuss in terms of kilowatt-hours.
BTU and BTU/h
British thermal units (BTU) are a measurement of heat used as part of the Imperial and US customary units. It is defined as the amount of heat required to increase the temperature of 1 pound of water by 1 degree Fahrenheit. Heat is a type of energy, so BTU can be directly compared to joules, calories, and kilowatt-hours (kWh).
- 1 BTU = 0.2931 watt-hours
- 1 BTU = 0.0002931 kWh
- 1 kWh ≈ 3412 BTU
BTU/h (BTU per hour) is a unit of power that represents the energy transfer rate. BTU/h is often abbreviated to just BTU to represent the power of appliances. For example, an AC marked with a label of 12,000 BTU actually has an energy transfer rate of 12,000 BTU per hour.
Horsepower and Tons
Horsepower (hp) is a unit of power most commonly used to reference the output of engines or motors. 1 unit of mechanical horsepower = 745.7 watts, and 1 unit of metric horsepower = 735.5 watts.
In the context of power, the "ton" refers to the ton of refrigeration. It is defined as the rate of heat transfer necessary to melt 2,000 pounds (1 short ton) of pure ice at 0°C in 24 hours. It is used mainly in the US to describe how well refrigerators and air conditioners extract heat (1 ton ≈ 3517 watts ≈ 12000 BTU/h).
Amount of Energy Used by Common Appliances
Below is a table showing the estimated energy requirements of various common household appliances. It is important to note that the requirements listed on the packaging generally reflect the maximum energy requirements. Typical usage likely results in lower energy use than stated.
| Common Appliances | Estimated Wattage (W) |
|---|---|
| Home Appliances | |
| Air Conditioner (HVAC) | 2,500 - 10,000 |
| Air conditioner (window unit) | 1,500 - 5,000 |
| Heater (home) | 5,000 - 20,000 |
| Heater (portable) | 750 - 2,000 |
| Humidifier | 25 - 350 |
| Dehumidifier | 200 - 750 |
| Fan (ceiling, table) | 15 - 200 |
| Light bulb (LED) | 3 - 25 |
| Light bulb (incandescent) | 15 - 200 |
| Electric water heater | 3,000 - 6,600 |
| Kitchen Appliances | |
| Refrigerator | 500 - 1,000 |
| Electric range/oven | 2,000 - 5,000 |
| Electric cooktop/stove | 750 - 5,000 |
| Microwave oven | 750 - 1,500 |
| Dishwasher | 1,200 - 2,000 |
| Coffee maker | 600 - 1,200 |
| Toaster | 750 - 1,500 |
| Electric kettle | 1,000 - 2,000 |
| Electric cooker | 160 - 1,500 |
| Other Appliances | |
| Electric vehicle charger | 1,500 - 20,000 |
| Television | 25 - 500 |
| Washing machine | 400 - 1,500 |
| Clothes dryer | 1,800 - 5,000 |
| Clothes iron | 750 - 2,000 |
| Hair dryer | 750 - 2,000 |
| Desktop computer | 100 - 250 |
| Laptop computer | 35 - 150 |
| Smart phone charger | 5 - 25 |
| Water pump/motor | 750 - 2,000 |
Energy Saving Tips
Implementing even a few of these tips can lead to significant savings on your electricity bills:
- Monitor your habits: Consciously tracking your energy habits (turning off lights, using a standing fan instead of AC, washing smaller loads) can have a significant effect on savings.
- Replace older light bulbs: A typical incandescent bulb requires 75W while an LED only requires 9W. LEDs cost more upfront but lead to significant future savings.
- Install a programmable thermostat: A large proportion of energy cost is due to heating/cooling. Adjusting the thermostat to suit your usage needs saves money.
- Shop for efficiency: Purchasing appliances with high energy efficiency ratings pays off in the long run.
- Check your windows: Heat loss through windows is common. Use curtains or blinds to obstruct sunlight during hot days, or upgrade to energy-efficient windows.
- Insulate your home: Poorly insulated windows, doors, attics, and walls lead to higher heating and cooling bills.