oil-fired space heaters, and gas-fired and oil-fired furnaces.

UNIT HEATERS

In this manual the term unit heater is defined as an installed equipment item and a component of a system consisting of an extended finned heat transfer surface (coil) and a propeller or blower fan to create airflow through it. Unit heaters are indirect units that differ from space heaters because they generate heat indirectly from a medium of steam or hot water piped through a central distribution system. Space heaters are direct-fired units that generate heat directly by the use of an electrical coil or by a combustible fuel.

Unit heaters can be used for many heating requirements, the major limiting factor being the availability of a steam or hot-water system. They are commonly used with heating systems in shops, offices, dining halls, and warehouses. There are three basic types: (1) the suspended horizontal discharge, (2) the suspended vertical discharge, and (3) the floor-mounted or horizontal type of blower unit (fig. 4-2).

The units are rated in Btu or equivalent direct radiation heat output and cubic feet per minute air discharge capacity at a given fan or motor speed. These ratings are important in the application of unit heaters.

Figure 4-2. - Unit heaters: A. Suspended vertical discharge; B. Suspended horizontal discharge.