In the light of the last updated European standard series EN 14961 (Solid biofuel - Fuel specification and classes) seems to be necessary the need and the will to provide more pellet tests under general requirements and standards in order to asses, compare and analyse different tests for different quality of products. The real objective of this European Standard is to provide unambiguous and clear classification principles for solid biofuels, to serve as a tool to enable efficient trading of biofuels and to enable good understanding between seller and buyer and between equipment manufacturers. The classifications given in this European Standard are provided with the objective of using biomass as a biofuel, and therefore do not deal with all other uses. In this framework, European Commission supported the BioNorm II project, with the main objective carry out a pre-normative research in the field of solid biofuels in close collaboration with the work of CEN TC 335. The general aim of the combustion boiler tests, in line with the Bionorm II project carried out in the Test Laboratory of RTU-IESE (Riga Technical University – Institute of Energy Systems and Environment), was to analyze the pellet quality parameters and properties that affect emissions and efficiency of a domestic wood pellet boiler. In particular six different combustion tests with 3 different types of pellets has been carried out using a typical wood pellet boiler produced by a Latvian manufacturer with a nominal power output of 15kW. In order to provide a better comparison for the present study the results of five previous boiler tests, always executed with the same boiler has been taken into account. The main objective of this paper is to show how the final combustion efficiency is affected by the pellet quality parameters and how much this is evident in the final products of the combustion test. The main normative EN 303-5 about testing of heating boilers for solids fuels was taken into account for all measurements.