RADISSON, Wis. - Two adults and their 4-year-old grandson are dead of apparent carbon monoxide poisoning, authorities in Sawyer County say.

The Sawyer County Sheriff's Office received a call about three unresponsive people in a Radisson, Wisconsin residence at 11:20 a.m. on Sunday.

According to the sheriff's office, emergency crews responded and found two adults and one child deceased inside the residence. They have been identified as Steven Michael Ryan, 61; Carolyn Marie Rindahl, 60; and their 4-year-old grandson.

Authorities say all three showed signs of carbon monoxide poisoning, and carbon monoxide was detected inside the residence. Toxicology results are not yet available.

Preliminary indications are that a recently improperly installed furnace was to blame, according to the sheriff's office.

The incident is still under investigation.