Electric unit ventilators (similar in design to heaters) are used to heat, ventilate, and cool large spaces that are by nature subject to periods in which there will be a high density of occupancy. They are frequently found in offices, schools, auditoriums, and similar structures.

The basic components of a typical unit ventilator are:
1. the housing
2. motor and fans
3. heating element
4. dampers
5. filters
6. grilles or diffusers

Automatic controls activate the unit ventilator and vary the temperature of the air discharged into the room in accordance with room requirements. Outdoor air is drawn through louvers in the wall and into the unit ventilator before being discharged into the interior of the structure. These ventilators are usually floor or ceiling mounted depending on the design of the room. In addition to electricity, unit ventilators may also be gas-fired, or use steam or hot water as the heat medium.