WATERVILLE — An air conditioning unit probably was the cause of a fire that damaged a home early Wednesday afternoon on Western Avenue.

Waterville Fire Department Lt. Mark Hamilton said the fire at 108 Western Ave. appears to have been started by a small electrical device. Overall the damage wasn’t extensive, he said, and the house probably sustained moderate water and smoke damage.

Hamilton said girls who lived in the house noticed smoke in the walls when they came in, notified the Fire Department and rescued four pets that were inside: two cats, a rabbit and a ferret.

Chief David LaFountain said the fire was accidental, and it was unlikely that the state fire marshal’s office would be called in to investigate. He said usually the fire marshal’s office gets called in if firefighters cannot put together a definite ignition sequence for the fire.

LaFountain said the damage was contained mostly to two rooms and the fire was discovered at its initial stage. Had it been discovered later, it could have caused more damage. The white house on Western Avenue has a metal roof, which he said could have been difficult to work with had the fire been burning longer.

“It didn’t get too far ahead of us,” LaFountain said.

Crews from Waterville and Winslow went to the scene, where the fire was knocked down quickly, LaFountain said.

Teenager Olivia Romero, who lives in the house, said she saw the smoke and ran back into the house to let the pets out. She said there was no smoke inside when she went in, but there was smoke outside near the air conditioning unit. She said she called 911 because she knew her family wouldn’t be able to contain the fire on their own. Romero said the house is almost 100 years old and thinks the wiring is old as well. She said her family has lived in the house for about 20 years.

Romero’s mother, Melanie Hayat, said no one was home at the time of the fire. She said she was out running errands, was gone for maybe a half-hour, and when she came home there was smoke. The girls called the fire in, and Hayat said she didn’t even see the smoke.

“I don’t know what happened,” she said, but as she was driving back on Western Avenue, she saw the firetrucks and had a “sinking feeling.”

Kierra Romero, Olivia’s older sister, was holding the ferret named Peanut as fire crews finished on Wednesday afternoon at the scene. She said she saw firetrucks fly by on Western Avenue and didn’t see the fire, but saw firefighters run into the house.

At the time, Olivia Romero said she didn’t think there was an actual fire, since there was no smoke inside.

LaFountain said the family was lucky the fire was discovered so early, as it could have caused more damage, had it been burning longer.

Colin Ellis — 861-9253

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Twitter: @colinoellis