The Valatie Hannaford was evacuated Monday night after three separate carbon monoxide detectors went off. Niverville, Valatie, and KJinderhook firemen responded just after 7:30. The elevated C.O. levels were traced to a heating unit on the roof. According to fire officials, snow was blocking a vent. The town building inspector was called to the scene. There were no reported injuries. Firemen were on the scene for two hours.