Is the dishwasher really more efficient?
It feels like washing by hand must be the frugal choice, but most measurements say otherwise. A modern dishwasher heats a small amount of water and sprays it again and again, while a running tap sends hot water straight down the drain. The calculator compares both methods over a year, counting water, the energy to heat it and the dishwasher’s electricity.
The calculation
- Loads per year = loads per week × 52
- Dishwasher: water = loads × water per cycle; energy = loads × kWh per cycle (water heating is included)
- By hand: water = loads × water per load; energy = hot water in liters × 0.0465 kWh, the energy to warm 1 liter by about 40°C (72°F) with an electric water heater
- Cost = energy × electricity price + water × water and sewer price
Example
A family runs the dishwasher 5 times a week. It uses 4 gallons and 1 kWh per cycle. Washing the same dishes by hand would take 20 gallons, 60% of it hot. Electricity costs $0.17 per kWh, water and sewer $12 per 1,000 gallons:
- Loads per year: 260
- Dishwasher: about 1,040 gallons and 260 kWh, costing $57 a year
- By hand: about 5,200 gallons and 549 kWh of water heating, costing $156 a year
- Saving with the dishwasher: about $99 a year
What changes the result
- Full loads: running a half-empty dishwasher doubles its cost per dish.
- Eco mode: lower temperature, longer cycle, less energy.
- No pre-rinse: scraping is enough; rinsing under the tap can add up to 20 gallons per load.
- Careful hand washing: with two basins and no running water, hand washing can use 8 to 10 gallons, closing much of the gap.
- Gas water heater: if your hot water comes from gas, the hand-washing energy costs less than with the electric rate used here.
- Air dry: turning off heated drying saves energy.
Beyond the money
A dishwasher also washes at higher temperatures than hands can bear, which helps hygiene, and saves time: roughly an hour or more per week for a family. Its manufacturing footprint is spread over about 10 years of use.