RADISSON, Wis. (AP) — Authorities say an improperly installed furnace may have caused the apparent carbon monoxide poisoning deaths of a couple and their 4-year-old grandson in northwestern Wisconsin.

A caller reported three unresponsive people on Sunday. Authorities found two adults and a child dead in the home in the small town of Radisson.

WDIO-TV reports the victims are identified as 61-year-old Steven Michael Ryan, 60-year-old Carolyn Marie Rindahl and their 4-year-old grandson. The Sawyer County Sheriff's Office says all three victims showed signs of carbon monoxide poisoning, and carbon monoxide was found in the home.

Sheriff Doug Mrotek says a recently installed furnace apparently was installed improperly, and that may have led to the deaths.

The deaths remain under investigation pending toxicology results.