Tourists in Chicago's John Hancock building during January's cold snap.
Tourists in Chicago's John Hancock building during January's cold snap. - 

The Department of Energy is predicting lower heating costs this winter. Some homes could see a nearly 40 percent drop in their heating bill. There are a couple forces behind this, and the federal Energy Information Administration has a wealth of data. Here's what you need to know, boiled down to three charts.

The Polar Vortex took our natural gas 

Natural gas is used to heat 57 percent of homes. Prices are on the rise after last winter's bitter temperatures depleted supply. Even if this winter is 10 percent warmer than expected, the EIA projects supply still won't have recovered to prior levels in 2015.

This winter will be much warmer

Last winter hiked up natural gas prices, and electricity followed, but the EIA is predicting demand will fall faster, especially when compared to last year's bitter polar vortex conditions. Heating days  a national measure of demand, waited by population  are expected to fall sharply for winter 2014-2015, following a decades-long trend.

That means lower bills for (almost) everyone

Even if this winter is 10 percent colder than predicted, the EIA says propane and heating oil users will see drops in their bills. As it's forecast now, demand will outpace higher prices and mean discounts across the board.

Of course, needs vary across the country, the energy department has an interactive tool that lets you explore spending state-by-state.

Follow Tony Wagner at @tonydwagner