A Sunday night fire at 1 McKayla Drive in New Milford was "not intentionally set," said deputy fire marshal Brian Ohmen.
Fire marshal Karen Facey said Monday the fire had been "accidental."
"It was an issue with the dryer," Ms. Facey said. "What exactly went wrong will be determined after the insurance company investigation is underway. We can't interfere with their evidence."
"This is a good reminded to people not to run their dryer when they go to bed or are leaving the house," she added.
Firefighters from the Water Witch Hose Co. No. 2, Northville and Gaylordsville volunteer fire departments were joined by Brookfield and Bridgewater fire departments to fight a blaze called in Sunday at 10:26 p.m.
The residents had been awoken by smoke detectors and exited the house, Mr. Ohmen said.
Residents of the home were not injured but one firefighter was transported to New Milford Hospital for heat exhaustion, Mr. Ohmen said.
The state fire marshal's office was called to the scene to provide lighting.
The 2,684-square-foot Colonial-style home incurred extensive damage to the kitchen and garage and heavy smoke damage to the second floor, where the four bedrooms were located, Mr. Ohmen added.
Firefighters cut the roof for ventilation during battling the blaze, he said.