Salt Lake City Fire Department officials said a malfunctioning water heater in the home was the cause.
Fire officials say the occupants of the home woke feeling ill with flu-like symptoms.
Officials say the residents called 911, and a hazmat team determined it was CO that was sickening the family.
They were taken to a local hospital for treatment.
Fire officials said the home did not have any CO sensors, and warned the public to have such devices installed to prevent sickness and death that can be caused by CO poisoning.