In this paper, experimental data are presented on emissions from a boiler of 40 000 kcal h-1 thermal capacity used for central heating. Five fuels were tested, with a span of cetane index from 24 to 47 and sulphur content from about 0.13 to 0.33% wt; thus they covered the spectrum of current EEC specifications for heating oils. Among the conclusions are that a boiler's efficiency falls with rising cetane index, whereas the level of emitted particulate falls with rising cetane index but rises with sulphur content. Similar increases are observed for the emitted SO2, which exhibits an almost linear behaviour relative to sulphur content. The NO(x) values fall with rising cetane index; the important observation here is that the accepted international limit NO(x) value of 120 mg m-3 at 3% O2 could not be attained even with the 'best' fuel used; this highlights the importance of using low-NO(x) burners.