The alarm was raised when smoke was seen rising from the window, Mr Ide said yesterday.
The fire had spread from the head of the bed to the wall and the ceiling in the short time it took for the property-owner's granddaughter to wake her and get her outside, he said.
Fire crew managed to contain the fire, which happened about 4.30pm on Saturday, to the room.
Furniture, toys, books and clothes in the room were destroyed, and much of the rest of the house was damaged by smoke.
The house was insured, but the contents were not, Mr Ide said.
The fire was being treated as accidental, he said.
It was likely it started in a relatively new electric blanket which had been left on to warm the bed.
It was a timely but unfortunate reminder not to leave electric blankets unattended for any length of time, and to turn them off at the wall when not in use.
