This study is focused on the use of biodiesel in a liquid fuel heating boiler of 26.7 kW. The influence of biodiesel/diesel mixtures, air flow rate, and input pressure on a combustion process for heating purposes was analyzed. The study is divided into two parfs. The first one deals with the characteristics of biodiesel as a heating fuel and the analysis of its properties and preparation method. The biodiesel was produced from sunflower oil in a pilot plant of 250 L/charge and was characterized according to standard norms. It was found that biodiesel is not acceptable as fuel for internal combustion engines (ester content of 92%). The second one deals with the effect of the operating variables on the combustion parameters in the boiler. The tests were conducted on experimental facilities and the generated emissions were analyzed. It was found that increasing the input burner pressure involves a decrease in CO and O-2 and an increase of CO2 in the fumes, as well as an increase in the combustion process yield. Likewise, a greater air flow rate gives rise to a decrease in the latter parameter. Moreover, CO emissions were slightly higher when biodiesel content was increased in the mixture, and therefore the combustion yield decreased. (C) 2013 Elsevier Ltd. All rights reserved.