A thermal model has been developed for the heating of a greenhouse by using inner thermal curtain and natural flow of geothermal warm water through the polyethylene tube laid on its floor. The calculations were done for a typical production greenhouse with the climatic data in the central part of Argentina during winter period. From the energy conservations point of view, the greenhouse has been divided into three zones i.e., zone I (plants under thermal blanket), zone II (space under ceiling) and zone III (space between roof and ceiling). The model has been tested with the published experimental data of air temperatures in zone I and zone II of the greenhouse. From the results, it was observed that the temperatures of air surrounding the plant mass in zone I were maintained in the range of 14-23 degreesC during winter night and early morning resulting in the better growth of winter growing plants against the harmful freezing effects. The predicted values of air temperature both in zone I and zone II of the greenhouse obtained from the proposed model exhibited fair agreement with the published experimental values. (C) 2003 Elsevier Ltd. All rights reserved.