Unit heaters are intended for the heating of air to balance heat losses in rooms or buildings. Compared with other types of heating systems, unit heaters (a) are usually lower in first cost; (b) are more easily controlled, either manually or thermostatically; (c) provide air circulation without heating during summer months.

Normally, operating controls are obtained separately from the basic unit in order to be procured at lower cost (see 3.1 and 6.2). Characteristics of thermostats include such items as electric voltage, pneumatic pressure range, on-off control, proportional control, heating and ventilation, heating only, temperature range, night set-back.

When an extremely saline atmosphere exists, manufacturers should be consulted for the availability of suitable corrosion-resistant material (see 3.6.3 and 6.2). Cast iron elements are available that resist external corrosion and are rated at 250 psig pressure.