On Tuesday night a fire engulfed a building on Galloway Rd.
The owners, who live on a separate part of the property, used it to house friends and family. No-one was in the building at the time.
Central-North Otago fire risk management officer Stuart Ide said the fire was probably caused by a mattress being leaned on a heater, which turned on the heater's switch.
This probably happened more than a few days before the fire, he said.
People should be careful when placing things on heaters not to flick the switch, but "at the end of the day it was an accident'', he said.
The heater was sent away for testing to confirm this was the cause.
The fire began in a bedroom and spread to the rest of the house, causing "considerable structural damage'' throughout the building, he said.
"It was very destructive.''
The building had a working smoke alarm.
Homeowner Chris Robinson said it took him and his wife a while to realise the building was on fire, and they were eventually called by a neighbour.
"Flames were coming right out the windows, then it crawled into the roof and just ruined everything inside.''
The building was insured, he said.
The fire brigade were "brilliant'', he said.
"They got straight on to it and did a good job.''
