Fed: Dec. best factory output growth month in 5 years WASHINGTON - U.S. factories boosted output last month, and December ended up being their best month for growth in five years. Busier factories are helping drive the economy. The Federal Reserve says manufacturing output increased 0.7 percent in January. And it soared 1.5 percent in December. December's figure was revised sharply up to the biggest gain since December 2006. Overall industrial production, which includes output by mines and utilities as well as factories, was unchanged in January. Utility output fell 2.5 percent, the second straight sharp decline due to an unseasonably warm winter that has cut demand for heating. Mining production also declined. Industrial production was revised up in December to 1 percent, the most in a year.