This method is known as spot brooding. A large area around the brooders is warmed to the same temperature when whole house brooding. The chicks have no choice between warm and cool areas. To save energy, however, the brooding area is reduced to the minimum amount needed for the size of chicks. As the chicks grow, the brooding area is increased in accordance to their sizes.
Good ventilation is essential with all brooding systems but especially partial-house brooding.
Light the brooders 24 hours before the chicks hatch or arrive. In time of stress or vaccination reactions, increase brooder temperatures about 5 above the recommended temperature until the chicks recover. Locate the guard 3 to 4 feet from the edge of the brooder. The guard prevents floor drafts and keeps chicks near the heat. In summer, enlarge the ring to keep chicks from getting too hot.