To reduce costs for heating and ventilation, sometimes partial brooding is applied, especially during the brooding period for breeders. This is a good practice as the staff can focus on a limited space, and the higher density of birds is not that crucial in the first days/week of the brooding period.

However, nowadays more breeder rearing houses are equipped with a tunnel ventilation system, where minimum ventilation is provided by side wall inlets but the extraction of the air is in one side of the house. This means that partial brooding will limit the ventilation of the bird area if the ventilators are behind the curtain. And if the heater is an open fire type which brings the carbon dioxide in the house, and it is placed in the front of the house in the bird area, it might be that the carbon dioxide is not adequately removed from the bird area if the tunnel fans are operating behind the curtain that is used for partial brooding.

To overcome this problem, and extra fan should be placed in the front of the house specifically for the period of partial brooding, or an opening should be made in the curtain to allow the air to leave the area where the partial brooding is done. To avoid unnessecary loss of air, a lose flap over the gap can be constructed on the side of the ventilators. In this way, the negative pressure created by the ventilators will open the flap over the gap, and air can move, where the gap is closed when the ventilators are not running.