How this calculator works
Both kinds of dryer use energy to heat air, and both are billed by the energy they consume. An electric dryer turns electricity into heat at nearly 100 percent efficiency, so its energy per load is simply the power rating multiplied by the cycle time. A gas dryer burns gas instead, and much of that heat leaves through the vent, so only part of the rating reaches the clothes; the efficiency input accounts for the difference. Multiply the cost of one load by the number of loads in a year to get the running cost. Purchase price, venting and the price of gas in your area decide whether the cheaper dryer is worth switching to.
Formula
electric energy per load = power x cycle time. gas energy reaching the clothes = rated input x cycle time x efficiency. cost per load = energy x price per kWh. cost per year = cost per load x loads per week x 52.
Worked example
A 5 kW electric dryer taking 45 minutes uses 5 x 0.75 = 3.75 kWh a load, which at 15 cents per kWh costs $0.56. A gas dryer rated 5.9 kW for the same 45 minutes at 60 percent efficiency delivers 5.9 x 0.75 x 0.6 = 2.66 kWh to the clothes, which at 5 cents per kWh costs $0.13. Five loads a week is 260 loads a year, so the electric dryer costs $146.25 and the gas dryer $34.52.
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Frequently asked questions
Why is a gas dryer rated in kW when it burns gas?
The rating is the energy input converted to a common unit so it can be compared with electricity. A 20,000 BTU per hour burner is about 5.9 kW. The cost still comes from the gas price, not the electricity price.
Is the efficiency really only about 60 percent?
For a vented dryer, a large share of the heat goes out with the moist air. The exact figure varies by model, so use the number from the manual if you have it; condensing and heat pump dryers are different machines with different figures.
What about the cost of a gas line and venting?
A gas dryer needs a gas connection and a suitable vent, and those costs can outweigh years of savings. Add any installation cost to the purchase price before deciding.
Does the calculation include the motor and controls?
The electric figure uses the whole dryer rating, so it already includes the motor. For gas, the small electricity use for the drum motor and controls is ignored, which is a few cents a year.