A faulty 3-inch metal flue pipe was the suspected cause of an early Monday morning fire at the Guerneville Lodge that hospitalized six people, according to a Russian River Fire Protection District captain.

The pipe from a pellet-burning stove located in the main hallway of the lodge at 15905 River Road in Guerneville led to a closet in a second-floor guest room where the blaze originated, Capt. Ryan Lantz said.

"Some material, possibly embers, escaped from the pipe," Lantz said. "We're not sure how it malfunctioned."

Smoke from the fire woke up the couple staying in the room, he said.

"They noticed the closet door was red or turning red," Lantz said.

When they opened the closet door, oxygen spread the blaze to the room and to an outside deck, then to three rooms on the third floor, he said.

The fire district was alerted of the blaze at 3:45 a.m., while couple who were staying in the room of origin and at least one other person alerted other guests to the blaze, Lantz said.

A kitchen adjacent to the second-story bedroom was badly damaged in the fire, as were 12 rooms, including a common living area. Four of the rooms were damaged by the fire and eight by heat and smoke, Lantz said.

The fire was contained around 4:30 a.m. and extinguished around 5 a.m. Crews were at the scene until 11:25 a.m., Lantz said.

Firefighters from Cal Fire, Monte Rio and Forestville also responded, he said.

Damage is conservatively estimated at $300,000, according to Lantz.

Four adults and two children went to Santa Rosa Memorial Hospital as a result of the fire. Five suffered smoke inhalation and one received a minor burn, Lantz said.

"We were fortunate there were no serious injuries," he said.