Many people have a misconception that running a dishwasher is more energy consuming than doing the dishes by hand.  I will explain the two scenarios as I go over the energy saving tips for washing dishes.  So you can decide on your own:

• Set water heater’s temperature at no higher than 120F, especially if you don‘t have a temperature sensor on your dishwasher or clothes washer. Here is why, it takes 1 kilowatt-hour to heat up 10 gallons of water from 80F to 120F. If your water heater’s thermostat is set at 140F, it will take 1.46 kilowatt-hour to heat up the same 10 gallons of water. That is almost one and half times more energy for the same amount of water. If your dishwasher does not have a temperature sensor, it will use the same amount of water from your water heater, whether its temperature is 120F or 140F. Most dishwashers have a minimum water temperature requirement of 120F, so any temperature above 120F would not make a difference in cleanliness of dishes.
• If you have to rinse your dishes before you put them into the dishwasher, rinse them with cold  water. Cold water does not require energy input.
• Run your dishwasher full.  The amount of energy used doesn’t change based on the load size.
• If you don’t like the idea of rinsing dishes with cold water, rinse them with warm water but don’t open the faucet all the way.  Open it just enough to get some flow and it will be just as effective as having the faucet fully open.  It will significantly reduce your hot water use.  Here is a test you can do.  All you need is a bucket of known volume (they usually come in 3- or 5-gallon sizes) and a stop watch.  Place the empty bucket in your kitchen sink, turn on the faucet at the same flow you usually rinse or wash your dishes and use a stopwatch to time how long it takes to fill up the bucket.  Then do the same experiment with using the low flow.  Here is what I got from my test:

1. The first time it took me just under 1 minute to fill up at 3-gallon bucket, Assuming that it takes you 10 minutes to rinse/wash your dishes, with the average water temperature of 100F, you will use up 30 gallons (3 gal * 10 min = 30 gal) of water at 100F. It will take 1.46 kilowatt-hours total to rinse your dishes (assuming your cold water is 80F, if it is lower, it would take more energy).
2. When I timed my low flow conditions, it took me 8 minutes to fill up the same bucket. This time my flow was 3gal/8min = 3/8 gallons per minute. For 10 minutes I would use 30/8 = 3.75 gallons total. It would only take me 0.183 kilowatt-hours to rinse my dishes. That is (1.46/0.183= 7.98) almost 8 times less energy use!

As a general guideline for the dishwasher use, most energy is spent on the hot water.  The mechanical operation of the dishwasher itself takes very low energy.  To find out how much energy your dishwasher uses, see my post Find Energy Use by Appliance.  Dishwashers use between 4 and 6 gallons of water per cycle.  Energy Star dishwashers use 4 gallons and non-Energy Star use 6 gallons.

So, how long would it take you to do a dishwasher full of plates by hand?  10 minutes, 20 minutes?  Using average water flow of 2 gallons per minute, you would use up to 20 gallons of water in 10 minutes and 40 gallons in 20 minutes.  Unless you’re using only cold water, using the dishwasher seems to be a more economical option to me!  And it’s a time saver too!!