States that heat losses in a heated-only building are normally evaluated by manual calculation methods and are a steady-state assessment of the load. On the other hand, buildings are operated on an intermittent basis, with the most common arrangement being that the system is on during the day and off at night. If the system is to reach its desired operating condition within a reasonable period of time, it follows that the size of the heating system must be based not only on steady-state heat loss, but also on the way in which the room in question reacts or responds to changes in load. Shows how a manual calculation method was derived which enables a designer to arrive at a sensible relationship between plant size and calculated load.

KEYWORDS: Calculating, intermittent heating, buildings, space heating, sizing, heat loss, designing.