The fire in a Viljandi apartment block that started on October 27 was started by a gas heater, the Rescue Board said on Tuesday.
The fire started inside the apartment on Toome tanäv and a male resident then threw the heater onto the balcony where it exploded and set fire to the surrounding area, including the roof.
The Rescue Center's Chief Inspector Roman Abubikirov said these types of devices can be used inside but enough space is needed.
It must now be clarified if the user requirements were followed and an investigation is in process, he said.
On Friday, two people were taken to hospital after inhaling smoke and the rest of the building was evacuated. No one was seriously injured.
The emergency services managed to get the fire under control before it spread to the nearby buildings.
Editor: Helen Wright