A malfunctioning water heater caused a fire at a north-side duplex Tuesday morning.

A 911 call came in just after 9:30 a.m. about a house fire in the 400 block of East Delano Street near the intersection of East Fort Lowell Road and North First Avenue, said Capt. Barrett Baker, spokesman for the Tucson Fire Department.

No one was home at the time the fire broke out and the second duplex unit was vacant, Baker said.

Firefighters pulled hoses through the front door and into the kitchen area where they found “heavy flames from the rear door of the unit with flames making their way up the wall and into the attic area. The ladder crew cut a hole in the roof to allow the smoke to escape the unit, also giving the crew better access to the attic area,” Baker said.

Firefighters had the blaze under control within 13 minutes.

“The cause was determined to be a malfunction involving the water heater on the back porch,” he said. “The flames spread to combustibles, including gasoline, which was being stored outside the water heater. The fire then spread upwards to the roof eaves.”

Baker did not have a damage estimate.