Natural ventilation is often expressed in “air changes per hour.” An air change per hour (ACH) means that the total volume of air in the stable is replaced in an hour’s time. Six air changes per hour means a complete air change every 10 minutes. Providing 4 to 8 air changes per hour will reduce mold spore contamination, minimize condensation, and reduce moisture, odor, and ammonia accumulation. For comparison, the modern home has 1/2 air changes per hour from infiltration through various cracks, such as around doors and windows. This recommendation for stable ventilation is substantially more than the average residential air exchange rate to maintain fresh air conditions and good air quality in the more challenging stable environment.
Natural ventilation uses openings located along the sidewall and ridge (roof peak) to accommodate these air movement forces. The sidewall openings are more important than the ridge openings if stable design cannot accommodate both sets of openings. The stable ventilation system will work better when both ridge and sidewall openings are provided. The ridge opening allows warm and moist air, which accumulates near the roof peak, to escape. The ridge opening is also a very effective mechanism for wind-driven air exchange since wind moves faster higher off the ground.
Circulation fans may be used in stables for temporary relief to disrupt warm, stale areas or to provide a cooling breeze over the horse’s body. These fans move air already in the stable so they do not provide more fresh air to the horse. A properly designed stable ventilation system should virtually eliminate the need for circulation fans.