Nine residential wood pellet boilers were tested for the emissions of carbon monoxide (CO), nitrogen oxide (NO), dust and combustion efficiency in real life and standard laboratory conditions and values were compared with the permissible values of Blue Angel, Swan Mark and EN-303-5. The test setup consisted of six boilers equipped with bottom feed burner (BF), one with top feed (TF) and two with horizontally feed burner (HF). Wood pellets used as fuel were DINplus certified. In real life conditions, 20 kW bottom feed boiler had the best performance. Emissions of dust from bottom and horizontal feed boilers were better in real life conditions than in standard laboratory conditions. All boiler technologies had lower combustion efficiencies in real life condition (2-5% less) than in standard laboratory condition. Top feed boiler emitted maximum CO (1566 mg N m(-3)); and dust particles from concerned boiler contained a considerable amount of elemental carbon. Almost similar NO, emissions were reported with all technologies in real life conditions. All the boilers met emissions and efficiency requirements of Swan Mark (except top feed boilers for CO) and EN-303-5, in both conditions. In laboratory conditions, all bottom feed boilers satisfied emissions and efficiency requirements of Blue Angel, however, in real life situation only 20 kW bottom feed and horizontal feed boilers could meet the concerned requirements. Bottom and horizontal feed boiler technologies have advantage over top feed, having lower emissions and higher efficiency. Keeping in mind minor variation in quality of considered wood pellets, different burner configurations clearly lead to important differences in the emissions and efficiencies. (C) 2011 Elsevier Ltd. All rights reserved.