Carpet and furnishings were set alight after loose coal fell from a fireplace.
Four crews were called to a house in Bourne Road in Folkingham just before 5.30am yesterday (Sunday) to deal with the fire.
Initially several people were thought to be inside the building, but by the time the firefighters arrived they had escaped unhurt.
The crews were then able to put out the flames.
The fire is thought to have been caused by a hot coal falling from an open fire grate in the house, causing severe smoke damage to the living room and setting fire to a small section of carpet and a leather armchair. The flames then triggered the smoke alarm.