Fire crews from Chulmleigh, Crediton and South Molton arrived at the scene in Moorland View just before 3am.
The occupiers, two adults and two children, had opened the windows to ventilate the house but wished it to be checked and an ambulance was sent for.
The fire crews discovered the carbon monoxide had leaked from a coal fired range cooker. They extinguished the fire in the cooker and ventilated the property using two breathing apparatus, one gas detector, one covering jet, and one hose real were used.
The occupiers were treated by paramedics for suspected carbon monoxide poisoning and were then looked after by neighbours.