The calorimeter consists of a 3m x 3m hood that collects combustion gas which are extracted via a fan. Measurements of gas flow, temperature and gas concentration are taken to enable determination of the heat released rate associated with a fire. Items of furniture can be tested below the hood.

Directly adjacent to the hood is an ISO room that enables testing within an enclosure such that the heat release rate can be determined. The ISO room has become a standard form of room test that allows the evaluation of lining materials and gives a better indication of how they might behave in a room situation.