A McLean family of four escaped from their town house early yesterday after apparently being overcome by carbon monoxide fumes from a malfunctioning furnace, the second such incident in their home in a year, Fairfax County fire officials said.

The father, Yong Sik Choe, 48, of 7412 Eldorado St. was admitted to Fairfax Hospital after the fumes from what the officials said was an improperly installed air duct allowed the gas to accumulate inside the three-story town house.

His wife, Sun Ja Choe, 45, and their two children, Michael, 16, a student at McLean High School, and Sung Ah, 18, who attends Parsons School of Design in New York City, were treated at the hospital and released.

It was the second time that the family has had problems with their furnace, according to Michael Choe. After being told last year that their furnace was not drawing enough air, the family broke two panes of glass in the basement to let in more fresh air, Choe said.

Sgt. Larry Hanger of the Fairfax County Fire and Rescue Department said county inspectors yesterday found the same problem: an apparently improperly installed duct was not providing the furnace with a sufficient amount of air. Choe said furnace workers were in the town house yesterday, attempting to resolve the problem.

Choe said he awoke at 4:45 a.m. to hear his mother groaning. "She was yelling for my dad," he said, "and she sounded really bad."

Choe tried to stand. "My stomach felt pretty funny. I felt like I was going to throw up. I was pretty dizzy." He went downstairs, where he found his mother lying on her side, near the open front door.

He said his memory was blurred, but he also recalled his sister fainting as she went into the kitchen to telephone for help. He said he remembered lying on the living room couch, concentrating on trying to breathe.

Choe said he didn't have the strength to reach the door and dimly remembered rescue workers coming to the door and saying about his mother: "This one's passed out, too."

The family has rented the town house for eight years and Choe said that his sister became "really sick" when furnace fumes had filled the house last year. "I just had a headache."