Both lodge types can be present at a beaver site. During the summer, beavers tend to use bank lodges that are cooler than the surrounding air. They use open-water lodges during the winter, whose temperature is similar to that of the surrounding water. The air vent provides ventilation, and carbon dioxide can clear out in 60 minutes. The amount of oxygen and carbon dioxide in a lodge changes little with the seasons. During the winter, warm air coming out of the vent helps to melt the snow and ice on the lodge.