That warm, relaxing, open fire likely is costing you a lot of money. First, firewood isn’t cheap if you need to purchase it. Second, the radiant heat may feel nice when you’re directly in front of the fire, but the already-heated air from the rest of your house is being sucked up the chimney. This makes your heat pump or furnace run longer. Third, if there’s no damper on the fireplace or the fireplace isn’t fitted with its own outdoor air source, indoor air is escaping up the chimney when the fireplace isn’t in use.
Outside air can help
Adding a source of combustion air that ducts into the fireplace can help a great deal – and it works well in combination with glass doors. The fire then will draw the air it needs for proper combustion and draft from outside, rather than conditioned air from inside.
However, the best tip is to avoid us-ing the fireplace in extremely cold weather. All of the indoor air lost up the chimney is being replaced by cold air drawn indoors through leaks in your home’s exterior walls. During milder weather, the air leaking indoors isn’t quite as cold, so it takes less energy to warm it.
Slightly opening the closest window to the fireplace and closing the door to the room also will help, because much of the excess air being drawn up the chimney will be outdoor air from the open window. When sitting right in front of the hot fire, you probably won’t notice the chilly breeze.