High temperatures in September drove people to keep their air conditioners running, boosting electric generation above levels seen a year ago, a federal report said.

The nation's net generation increased 6.2 percent in September compared to September 2017, according to the Energy Information Administration.

"This increase in electricity generation occurred because the country, as a whole, experienced a very warm September this year compared to the previous year," EIA said in its Electricity Monthly Update released Nov. 27.

"At the regional-level, almost all parts of the country saw an increase in electricity generation compared to the previous September, with only the Western region seeing electricity generation remain relatively flat compared to September 2017."

Coal wasn't necessarily the fuel of choice, the study found. Compared to September 2017, coal use was mixed throughout the country, with increases in the Northeast, central region and Southeast and decreases in the mid-Atlantic, West, Florida and Texas.

In fact, EIA found that in September, U.S. coal stockpiles reached their lowest point, 101 million tons, since 2005.

Meanwhile, all regions of the country saw an increase in natural gas generation. "For the second consecutive month, the southeast and central regions saw the largest increases in natural gas generation, up 6,691 and 4,028 gigawatts respectively, compared to the previous year," the report said.

EIA also examined outage durations for 2017 in its latest report. Last year, major weather events caused the average U.S. electric customer to lose power for 7.8 hours, or 470 minutes, which is double the length of outages in 2016, the agency said.

Yet, EIA noted, "when excluding major events, the average duration of interruptions customers experienced was almost identical in 2016 and 2017."