Clunes CFA lieutenant Brad McNeight said the fire, caused by an electrical fault in a chest freezer, started just after 3pm in the laundry, quickly spreading up the walls and along the roof.

The woman, who was home alone taking a nap, was woken by the smoke detector.

"The smoke detector alerted her and that's what working smoke detectors do,'' Mr McNeight said.

"We don't know the scenario, if she would have woken without the smoke detector or not.''

Mr McNeight said the woman did a good job of trying to extinguish the fire with a garden hose until the CFA arrived.

Three CFA crews from Clunes and a pumper from Creswick attended the fire which took 20 minutes to extinguish.

Mr McNeight said fire caused about $70,000 of damage to the house.

"It travelled through the roof of the whole house,'' he said.

"There was smoke damage, water damage, all the tops off the doors have been burnt off.

"The computers have melted and the TVs have melted because of the heat.''