Electric dryers have a higher efficiency rating than gas dryers, but energy losses at power plants dispensing electricity make gas dryers more energy efficient overall in most cases. Gas dryers also typically cost less to run.
Electric dryers convert most of the electricity they receive into heat, which is then applied to the clothing. This efficiency rating, however, does not take into account the efficiency losses at the electricity's point of origin. Coal and natural gas are the two most common fuel sources for power plants, and a considerable amount of energy is lost converting heat into electricity. Gas dryers, which use the heat generated during combustion to heat clothing, use natural gas more efficiently than electricity from a natural gas power plant.
Gas dryers generally cost a bit more than their electrical counterparts, but they are cheaper to run and quickly make up for the price difference. Gas dryers also generally operate at a higher temperature, which leads to faster dryer cycles.
Newer technology may change this, however. Some ventless dryers use heat pumps to extract water vapor from the dryer, and these models do not vent away hot air. As a result, they can reuse hot air instead of constantly heating up cooler air. These systems cost more upfront but have the potential to cut back on energy use significantly. As of 2015, nearly all ventless dryers run on electricity.