This Part of BS 845 describes a comprehensive procedure for conducting thermal performance tests on steam, hot water or high temperature heat transfer fluid boilers to give results within a tolerance of ± 2 percentage points¹⁾ and for presenting the results in tabular form. This Part makes use of both the direct and the indirect methods of test. Test results are based on either the gross or the net calorific value of the fuel.

This comprehensive procedure is suitable for all boilers, including those with multiple thermal flows to and from the boiler.