WASHINGTON — Cold snaps can run up heating bills, but sealing cracks and adding proper insulation around the house can result in big savings, according to an environmental group that promotes saving energy.

“You can save up to 15 percent on your energy bills,” Lauren Urbanek of the Natural Resources Defense Council said.

Warm air can escape homes from invisible cracks in walls, the attic, crawl spaces, recessed lighting fixtures and electrical outlets — especially outlets on exterior walls.

“Those (leaks) can add up to about the size of a basketball — a hole in the wall about the size of a basketball,” Urbanek said.

Adding weather stripping to doors and sealing cracks around windows are quick fixes.

“Grab a caulk gun and get around those windows,” Urbanek said, adding that leaky window issues can also be solved by installing storm windows.

Nine out of 10 homes in the U.S. are under-insulated, according to EnergyStar.gov, which offers homeowners guidance about proper insulation.

Here are a few quick fixes to help keep your home warm:

• Make sure the fireplace flue is secured properly when not in use
• Close curtains and blinds
• Change HVAC filters
• Use ceiling fans

A slowly circulating fan rotating clockwise will pull cool air up that then pushes warm air trapped on the ceiling down along the walls and back toward the floor.

To find out what you might be missing, local utility companies such as Pepco, Dominion Energy and Baltimore Gas and Electric offer customers energy audits.

“A professional will come to your home and do a full diagnostic evaluation,” Urbanek said.