oil-fired space heaters, and gas-fired and oil-fired
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.
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 disc harge.