As long as we're addressing large, costly holes in our home envelope, your chimney is a gaping one that goes in heat's favorite direction: up.
Although your chimney probably has a working damper, it's unlikely to be airtight. Poke your hand up inside the flue and you'll probably feel the draft.
"The majority of damping systems in a fireplace do not adequately seal off air infiltration from the outside," says Lindstrom. "You need to address that hole, because it's a big one."
Because masonry retrofits can prove costly and chimney caps are cumbersome during fireplace season, most homeowners opt to place fitted glass fireplace doors over this energy elephant in the living room. Some homeowners also leverage their fireplace by installing a heat exchanger, insert or woodstove to bring more heat into the room.
Cost: Glass fireplace doors run $300 to $500, woodstoves $700 to $1,200, inserts $1,400 to $2,300.
Savings: Glass fireplace doors can shave 1 percent to 2 percent off your heating bill.