Ventilation in livestock buildings serves four purposes: moisture removal, ammonia dilution, heat removal, and fresh air distribution. Winter and summer requirements differ by a factor of 10 or more. A 1,000-head finishing hog barn needs about 10,000 CFM minimum winter ventilation but 300,000 to 400,000 CFM for summer tunnel ventilation.
Getting ventilation wrong costs money in feed efficiency, animal health, and mortality. Pigs at 90°F eat 10% to 15% less. Dairy cows above 72°F lose 2 to 4 pounds of milk per cow per day per degree. Ammonia above 25 ppm causes respiratory damage. This guide covers ventilation rates, fan selection, tunnel ventilation design, and controls.
Ventilation Rates by Species and Season
Finishing hogs (150–250 lbs): cold weather minimum 10 CFM per pig, mild weather 35 CFM, hot weather maximum 120 to 150 CFM, tunnel ventilation 300 to 500 CFM per pig.
Dairy cows (1,400 lbs): cold weather minimum 50 CFM per cow, mild 170 CFM, hot weather tunnel 1,000 to 1,200 CFM. A single lactating Holstein produces 3,000 to 4,000 BTU/h of sensible heat and 5 to 7 gallons of moisture per day.
Poultry broilers (5 lb market): cold weather minimum 0.5 to 1.0 CFM per bird, hot weather maximum 8 to 10 CFM per bird. A 20,000-bird house needs 10,000 to 20,000 CFM minimum and 160,000 to 200,000 CFM maximum.
Finishing hogs: 10 (winter min) / 35 (mild) / 150 (hot max)
Dairy cows: 50 (winter min) / 170 (mild) / 1,200 (hot max)
Broilers (5 lb): 1.0 (winter min) / 5 (mild) / 10 (hot max)
Beef feedlot (shelter): 20 (winter min) / 50 (mild) / 150 (hot max)
Livestock Barn Ventilation Calculator
Calculate ventilation rates for livestock barns by animal type and season. Covers dairy, beef, swine, and poultry with CFM per head, fan sizing at actual static pressure, and multi-stage ventilation planning from winter minimum to summer tunnel mode.
Fan Selection, Staging, and Efficiency
Always select fans based on CFM at your actual operating static pressure, not free-air rating which can be 30% to 50% higher. Tunnel barns operate at 0.05 to 0.08 in. w.c. Sidewall exhaust barns at 0.03 to 0.06 in. w.c.
High-efficiency 48 to 54 inch fans deliver 20 to 24 CFM per watt. Lower-quality fans deliver 12 to 16 CFM per watt. The efficient fan saves about $360 per year in electricity.
Fan staging manages the transition from minimum to maximum ventilation using temperature setpoints with 2°F to 3°F spacing between stages.
Tunnel Ventilation for Heat Stress
Tunnel ventilation creates wind chill by pulling air the length of the barn at high velocity. Design air speed: 400 to 600 fpm for hogs, 400 to 500 fpm for poultry, 500 to 700 fpm for dairy.
Required CFM = barn cross-section area × target velocity. A 43-foot-wide barn with 400 ft² cross section at 500 fpm needs 200,000 CFM — eight to ten 54-inch fans.
Cool cell pads at the inlet reduce incoming air temperature by 10°F to 15°F when humidity is below 60%. They add 0.06 to 0.10 in. w.c. static pressure that must be accounted for in fan selection.
Required CFM = Barn cross-section (ft²) × Target air speed (fpm)
Example: 43' × 9.3' avg = 400 ft²
400 ft² × 500 fpm = 200,000 CFM
At 24,000 CFM/fan = 8–9 fans needed
Ammonia Control Through Ventilation
Recommended maximum for animal health is 25 ppm. OSHA 8-hour TWA is 50 ppm. In practice, keeping below 10 ppm provides the best animal performance and worker comfort.
Minimum ventilation rate is the primary ammonia control tool. Under-ventilating to save heating fuel is false economy: ammonia exposure reduces feed efficiency by 5% to 10% and increases respiratory disease costs.
Supplemental strategies: frequent manure removal, pit additives that lower pH below 6.0, and dietary crude protein reduction. Reducing crude protein by one percentage point reduces ammonia emissions by roughly 10%.