Firefighters discovered the double-storey home on Winjeel Court docket in Braybrook "totally alight" once they arrived about 8.40am.
A 42-year-old Braybrook man died on the scene.
A 76-year-old Braybrook man was rushed to hospital in a severe situation brought on by smoke inhalation.
A neighborhood warning has been issued for individuals to concentrate on smoke within the space.
The precise circumstances surrounding the fireplace are but to be decided.
Arson police are set to research the scene.
Anybody with info is urged to contact police.