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By Larry Jacobson, PhD & Chuck Clanton, PhD

Ventilation or air exchange is needed in horse barns or buildings to control and remove moisture, pre-vent condensation on surfaces and maintain acceptable air quality by removing carbon dioxide, ammonia, hydrogen sulfide, dust, airborne pathogens and fumes during cold weather and to remove heat and hold down excessively high temperatures preventing heat stress in warm/hot conditions. This exchange of air or ventilation can be accomplished with a natural (non-mechanical) system that is driven by buoyancy (hot air rises) and wind forces or by a mechanical ventilation system that uses electrical exhaust fans along with planned designed inlet openings.

Natural Ventilation Systems…
The simplest system is an open front shed, pointing to the south. This allows the horse to get in out of the wind and/or rain and snow. This is adequate for the horse as long as they are well fed and acclimated to the current weather conditions.

An enclosed naturally ventilated barn must have sidewall vents or eave openings (inlet) and a ridge or roof chimney openings (outlet). Conditions inside these enclosed facilities are typically at or slightly above outsides temperatures, year round, but are generally draft-free and when combined with dry bedding can provide a comfortable environment for mature and healthy horses. The advantage of natural systems is economics, but control of airflow and air distribution is not as good. These barns should have heated water lines and tanks to prevent them from freezing during cold conditions.

Mechanical Systems…
A mechanically ventilated barn is designed for year around conditions. During cold weather, minimal ventilation is needed to remove moisture generated from respiration and evaporation of spilled drinking water and urine and feces.

This cold weather ventilation rate should be 25 cubic feet of air per minute (cfm) per 1,000 lbs of horse. This cold air exchange rate is best provided by a continuously running sidewall exhaust fan. During mild weather add a second fan(s) that delivers an additional 100 cfm/ 1,000 lbs (total of 125 cfm/1,000 lbs of horse) with an indoor temperature controller (thermostat) set at about 50 F. During warm/hot temperatures another exhaust fan(s) sized at an additional 200 cfm/1,000 lbs (total of 325 cfm/1,000 lbs of horse) needs to be added to hold down excessive temperature rises in barns with a separate (or a single multi-stage) temperature controller set to activate at about 60 F. A mechanically ventilated barn needs designed inlets or someplace for air to enter the building. The inlets should be sized to provide 1 square foot of inlet area for every 600 cfm of exhaust fan capacity which should be evenly spaced throughout the barn to provide good air distribution.

Supplemental Heat…
During winter conditions, indoor temperatures may drop below acceptable levels and water lines could freeze. For these situations, a small gas-fired or electric space heater is need to maintain the minimum desired temperature. The heater should be sized at roughly 4,000 BTU/hour (gas) or 1 kW (electric) per horse. It should be noted that these space heaters are the number one cause of fires, so safety precautions need to be taken.

All housing needs to be well constructed (as air tight as possible for mechanical ventilation systems) and have insulated walls and ceiling. The insulation will keep the building cooler in the summer and prevent moisture condensation as well as keeping the building warmer in winter. For open sided and enclosed naturally ventilated barns, roof insulation with an R-value of 2 to 4 is strongly suggested to prevent condensation from forming on the underside of the roof in winter plus reduced heat load in summer. For mechanically ventilated barns, a minimum R-value in the mid-teens (15) is needed in the walls and mid-twenties (25) in the ceiling. A vapor barrier or retarder (sheet of plastic) needs to be placed on the warm side of the insulation in both the walls and ceiling to keep moisture from moving through the interior surfaces into the cavity which could deteriorate the building material.

Summer Management…
For mechanically ventilated barns in the summer it is best to keep the barn closed up and the exhaust fans and inlets operating to limit temperature rise inside the barn. Internal circulation fans can be used to increase airflow over horses but these do not exchange air in the building like the sidewall exhaust fans and should only be used to provide additional animal cooling. Under some special conditions, evaporative cooling systems, such as direct animal sprinklers or air inlet evaporative pads in the walls, have been installed in horse buildings. If a mechanical ventilation barn was only designed for the fall, winter, or spring periods (equal or less than 125 cfm/1,000 lbs of horse), then during the summer, open up the building and use natural ventilation. As soon as large doors and/or windows are opened up, exhaust fans are no longer of any benefit and should be turned off. If circulation or mixing fans are in the barn, they should be used to help move air over animals but keep in mind that air exchange will be dependent completely on wind forces for these types of barns.

Air Inlet(s) Location…
Contrary to popular belief, the way to eliminate dead air spaces in a mechanically ventilated barn is to place well distributed air inlets throughout the barn, not exhaust fans. Exhaust fan(s) location has little to no impact on the barn's air distribution. In a properly designed and operating mechanically ventilated barn, there will be a slight negative pressure and fresh air will enter the barn through any inlets and will provide fresh air to animals. To obtain good air quality in a box stall setting, make sure there is one or more air inlets located near the box stall.

Courtesy Universtiy of Minnesota
© Reprint BHHLLC 2015