Common Horse Stable Ventilation Questions

courtesy of eXtension

Although horse enthusiasts have a wide variety of riding-driving, disciplines, breeds, and interests, all agree that good air quality inside their horse’s stable is important. Veterinarians and professional horse handlers recommend good ventilation for stabled horses to maintain respiratory health. We know that the stable should smell like fresh forage and clean horses rather than manure or ammonia. Yet, failure to provide adequate ventilation is the most common mistake made in construction and management of modern horse facilities.

Although the emphasis is on stables with box stalls to each side of a central aisle, the principles are equally effective in Inadequate ventilation is the most common mistake made in modern horse facilities. maintaining good air quality in other stable layouts and in run-in-sheds or indoor riding arenas.

What Is Ventilation? The objective of ventilation is to provide fresh air to the horse. Ventilation is achieved by simply providing sufficient openings in the building so that fresh air can enter and stale air will exit. There are ways to provide each stabled horse with access to fresh air all the time. The stable will have “holes” in it to admit air; it cannot be constructed tight as a thermos bottle like our own homes. Compared to our homes, stables have much more moisture, odor, mold, and dust being added to the air, not to mention manure being deposited within the facility.

Ventilation is needed to remove heat from the stable in hot weather. It is beneficial to provide a cooling breeze over the horse, which is more comfortable than hot, still air. During warm weather the stable doors and windows are usually open to aid in moving air through the stable.

During cold weather, the stable is often managed with closed windows and doors to keep chilling winter winds off the horse. In winter, the ventilation goal changes from heat removal to controlling moisture, odor, and ammonia that have built up in the more closed environment of the stable. Moisture comes from horse respiration and other stable activities such as horse bathing and facility cleaning. With moisture buildup, comes increased risk of condensation, intense odor, more ammonia release, and pathogen viability, which contributes to respiratory infection.

Ventilation involves two simple processes. One is “air exchange,” where stale air is replaced with fresh air, and the second is “air distribution,” where fresh air is available throughout the stable. Proper ventilation provides both; one without the other is not adequate ventilation. For example, it is not good enough to let fresh air into the stable through an open door at one end of the building if that fresh air is not distributed throughout the horse stalls. Nor is proper ventilation satisfied if a tightly closed stable uses interior circulation fans to move stale air around the facility.

What are comfortable conditions? A horse’s most comfortable temperature range is between 45 and 75o F. Our most comfortable human temperature is at the upper end of the horse comfort zone. Clearly, horses tolerate cold very well and adapt to chilling breezes when housed outside. If conditioned to cold weather, horses with long-hair coats and adequate nutrition can withstand temperatures below 0oF. Even show horses with a short-hair coat can be maintained in a cold but dry indoor facility when provided with blankets and hoods. Within a box stall, horses have the freedom to move away from uncomfortable conditions.

What is a well-ventilated stable going to feel like? The stable environment in winter is almost as cold as outdoors but comfortably dry with no condensation dripping from the structure. Cold and humid conditions are uncomfortable for both horse and human and lead to a stuffy, dank environment within the stall. Upon first entering a stable, make an objective evaluation about its air quality before you have adapted to those conditions. In hot weather, the stable temperature will be within a few degrees of outdoors and more comfortable due to shading from the sun.

During winter, horse stables should be kept no more than 5 to 10°F warmer than the outside temperature. This guideline helps assure fresh air conditions, but it also means freezing will occur inside stables in northern climates. It is a management mistake with regards to air quality and to your horses’ health to close the barn tight just to keep conditions above freezing in cold weather. If condensation occurs on interior surfaces, then the stable is too closed off for proper ventilation.

Horse owners often want warm stable conditions for their comfort during horse care activities. Instead of heating the whole barn or cutting off ventilation to trap horse body heat, provide a heated grooming and tacking area. If freezing conditions cannot be tolerated, then supplemental heat will be needed in susceptible areas, such as the tack room or washing and grooming areas. Frostproof, self-draining hydrants and freeze-proof automatic waterers are available. Water pipes within the stable need to be buried to the same depth as supply plumbing to the stable site.

What about drafts? A draft occurs when cold air blows on a horse. Warm air blowing over a horse is not a draft. Since horses tolerate colder conditions than humans, what we consider drafty is not necessarily uncomfortable to the horse. Be sure to differentiate between cold temperature and draft. A main principle of ventilation is that even very cold fresh air can be introduced into a horse stall, so when mixed and tempered with stable air, it no longer has the air speed and chill of a draft.

What about air distribution within the stable? An open, unobstructed interior helps move air around the stable. Provide airflow between the openings in the stable where fresh air enters and stale air exits. Fresh air is brought into the horse stalls where it picks up moisture, heat, dust, and ammonia and can exit out another opening. Stuffy stables, and their poor air quality, are the product of limited air exchange and/or obstructions to getting the fresh air to where the horses are stalled.

Go into the horse stall to determine the air quality of the stable. Moisture, odor, and ammonia are generated primarily in the stalls, where fresh air is needed for horse respiration and to dilute air contaminants. Since most dust and ammonia are down near the bedding and manure, check air quality near the floor as well as at horse-head height. Floorlevel air quality is particularly important for foals or when horses eat at ground level and spend time laying in the stall. It is not uncommon for the stable’s working aisle to be breezy and well ventilated while the stalls suffer from stuffy conditions.

How much ventilation should be provided? 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. Provide 4 to 8 air changes per hour to 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.

How is ventilation provided to the structure? Natural ventilation is used in horse stables and riding arenas. Wind and thermal buoyancy (hot air rises) are the natural forces that drive this type of ventilation. 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 winddriven air exchange since wind moves faster higher off the ground.

Wind is the dominant force in horse stable natural ventilation. With the variability in wind speed and direction, openings on the stable will frequently alternate between being an inlet for fresh air and an outlet for stale air. Wind will push air into the stable through openings on the windward side of the building while drawing air out of the stable on the leeward, or downwind, side. Once the wind speed is above about 1 mph, wind-driven ventilation will dissipate the effects of thermal buoyancy in horse stables.

Since horse stables are typically unheated, they are considered “cold” housing. Thermal buoyancy (hot air rises) is dependent upon a temperature difference between the warmer stable interior, where the horses’ body heat will slightly warm the surroundings, and the cooler outside conditions. Because a properly ventilated stable has less than a 10°F difference between the stable interior and outside conditions, there is not a large temperature difference as a driving force for buoyant air movement.

What about using fans? The other major type of ventilation is mechanical ventilation, which uses fans, inlets, and controls in a pressure-controlled structure. Mechanical ventilation is typical in some types of livestock housing (poultry and swine) but is not commonly needed in horse stables. Natural ventilation is adequate for housing animals, such as horses and cattle, that are tolerant of a wide range of temperature conditions. Mechanical ventilation is more expensive to install and maintain but offers control over the air exchange rate. Heated stables may employ mechanical ventilation during the heating season. The fan(s) has a known capacity in cubic feet per minute (cfm) and provides a uniform air exchange rate. Minimum recommendations for each 1,000-pound horse are 25 cfm for moisture control in cold weather; 100 cfm for heat removal during mild weather; or 200 to 350 cfm during hot weather. Inlets are sized at 1.7 ft2 ⁄1,000 cfm of fan capacity.

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. Another application of mechanical ventilation uses a fan blowing air into a duct to distribute fresh air throughout a part of a stable where direct access to outside air is difficult. This duct system can be used in retrofitting older barns and is particularly effective in the underground portions of bank barns where access to fresh air is limited. Ducts can also effectively distribute supplemental heat in a barn.

Well-ventilated stables are necessary for horse health and are the hallmark of good management. There is a need to demystify ventilation; the objective is simply to get fresh air to the horse. Ventilation is primarily driven by wind forces, so good ventilation is achieved by allowing wind to bring fresh air into the building, while drawing out stale air.