Our hospital group is in the eastern part of Nagano Prefecture, and carbon monoxide poisoning is a common health problem during the winter season. To investigate the causes of carbon monoxide poisoning, we examined 67 cases of carbon monoxide poisoning that visited any of three facilities in our hospital group from January 1, 2016, to February 28, 2022. The most common cause of poisoning was heating appliances (48 cases, 71.6%). Among these, 41 cases (85.4%) involved charcoal briquettes. The risk of carbon monoxide poisoning increases when charcoal briquettes are used without proper ventilation. The results suggest that charcoal briquettes are used as a heating device without proper ventilation in this area, and providing residents with education about proper ventilation may prevent carbon monoxide poisoning.