To prevent freezing, a heating system should be installed rather than reduce or eliminate the ventilation. Rather than a continuous peak vent, these barns can be equipped with one or more chimneys for exhaust. Provide a total exhaust air-shaft capacity of 0.5 to 1.0 per cent of the stable floor area. A control damper with 90 per cent closing capability located near the top of the chimney will keep the chimney charged with warm air so that cold down drafts do not occur. The damper is usually controlled manually by cable.
Natural ventilation is the system of choice for most horse barns unless supplementary heat is added.
Doors and windows can provide the additional air openings needed but still require adequate management to prevent drafts overnight or during storms. This higher rate is necessary since air quality is still a function of the rate of air exchange rather than horse population. Ideally, ventilation designers would like to provide two air changes per hour to guarantee good-quality air. However, many barns are limited to one air change per hour to minimize heating costs. A good choice for barns housing less than 15 horses is a pair of variable speed fans with capacities of 300 to 1000 CFM and 1000 to 3000 CFM respectively.