Investigators are focusing their attention on a candle at a fire that caused about $150,000 damage Saturday.

The Calgary Fire Department was called to a fourplex in Tuxedo Park just after 10:30 a.m. Saturday. Crews arrived at 125 - 21st Avenue to find smoke showing on the top floor of the two-storey structure.

The department says crews were confronted by extremely heavy smoke as they entered the complex and were challenged to find access to the fire floor and the seat of the fire.

Just one of the four units in the building sustained damage, the fire department says, but the damage is significant and estimated at $150,000.

The first arriving captain said the well-constructed fire walls between the units in this building definitely contributed to the containment of the fire and curtailed fire loss, the department said in a release.

One firefighter was treated on the scene by paramedics for symptoms associated with dehydration.

The fire investigator on the scene is focusing on the area in which an unattended candle was reported to have been burning on the second floor.

Residents of the three unaffected units have returned to their homes.