A soil temperature up to 45°C is favourable for most crops and stimulates root growth, while higher temperatures can be harmful [5,12]. If the pipe temperature rises above this critical temperature the roots will not grow into the pipe and block the airflow. Hence, the system should be designed so that the pipe wall temperature reaches at least 45°C at the end of a daily irrigation. The pipe spacing should be designed so that the soil temperature and the irrigation rate between the pipes are suitable for the crop.