The invention provides a water heater shell, a main unit and a water heater. The water heater shell comprises a shell body and a first grid arranged on the shell body and used for air outflow. The first grid comprises a first grid part and a second grid part sequentially arranged in the first direction. The first grid part comprises a first air guiding plate perpendicular to the first direction, the first air guiding plate extends in the second direction, and the two ends, in the second direction, of the first air guiding plate are connected with the shell body, wherein the second direction isperpendicular to the first direction. The second grid part comprises a second air guiding plate extending in the second direction, and the two ends, in the second direction, of the second air guidingplate are connected with the shell. The distance between the second air guiding plate and the first air guiding plate is gradually increased in the shell direction from interior to exterior. According to the provided water heater shell, the provided main unit and the provided water heater, wind resistance of horizontal airflow and centrifugal airflow can be reduced, and the air outlet air volumeand performance of the water heater are improved.