Study of Large Scale Kitchen Range Hoods. A field study of six different large scale kitchen range hoods has been carried out. The aim has been to measure both how well a contamination produced under the hood is taken care of (hood efficiency) and the thermal comfort. The results have been compared with recommendations according to AFS (the National Board of Occupational Safety and Health) 1980:20. To get the influence of variation in energy input to heatsource and changes in exhaust airflow rate under control, a laboratory kitchen has been built up. The measured hood efficiency varies between 83 % and 95 %, with most of the kitchens in the range of 90-95 %. The equivalent temperature measured 0.5 m from a heat source, was in most cases about 28 °C with a maximum of 32 °C. One of the hoods was equipped with an internal injection of supply air. In this case we measured both a very high hood efficiency and a very good thermal comfort. Measurement in the laboratory kitchen showed that the hood efficiency depended very much on the exhaust airflow rate. Changes in the input energy to the heatsources gave only a minor dependence. To reach a hood efficiency of about 95 %, it seems necessary to maintain a mean velocity of at least 0.1 m/s into the hood cross-section. The thermal comfort is strongly depending on the input energy to the heatsources, and less on the airflow rate. With a conventional volume hood as a reference, it should be possible to compare different types of hoods in a laboratory.