Will the fire draw air from the outside or from inside the house for combustion?
As an example, an open type fireplace will use the oxygen right in front of it causing a vacuum and thereby pulling the surrounding air in to fill the void. A chain reaction occurs because of this and eventually it will draw outside air from the cracks/seals around windows and doors.
If standing next to the open fireplace you’ll roast, if sitting across the room you’ll freeze your ass off.
