Heat has returned to Hempstead High School after students and staff said they were forced to sit in bitter-cold classrooms for months.School officials said a truck that pumps hot water into the school's heating system was installed Thursday night.Dawn Sherwood, president of the Hempstead Teachers Association and a teacher at the school, says plans to upgrade air handlers in the school were never completed and that the heating system has not been fixed. Sherwood says she suspended the school's ban against hats in her classes so students could sit with their coats and hats on to stay warm. Some students told News 12 Long Island that it was very difficult for them to pay attention due to the cold.