# Broiler House Exhaust Fan Selection and Maintenance ## Key Takeaways - Fan capacity is quantified in Cubic Feet per Minute (CFM), with minimum ventilation requiring 0.5-1.0 CFM/lb of bird weight for moisture and air quality control in cold weather, while tunnel ventilation demands 1.5-3.0+ CFM/lb for heat stress management in hot weather. - Fan selection should prioritize models certified by AMCA or BET for verified performance data, focusing on CFM at specific static pressures (typically 0.05-0.15 inches of water) and efficiency ratings (CFM per watt) of 20 or higher for optimal energy utilization. - Regular maintenance, including weekly belt checks (replace if cracked, frayed, or glazed) and monthly cleaning of fan blades and shutters, is critical to prevent airflow reduction (up to 20-30%) and maintain operational efficiency. - Static pressure, a measure of resistance to airflow, should be monitored weekly using a manometer, with a normal operating range of 0.05-0.15 inches of water; elevated levels indicate potential issues like blocked inlets or dirty fans. - A comprehensive fan maintenance log, detailing cleaning dates, belt replacements, motor checks, and repairs for each fan, is essential for proactive management, troubleshooting, and informed replacement decisions. - Persistent respiratory distress, sudden mortality, or signs of ammonia toxicity unresponsive to ventilation adjustments within 24 hours necessitate immediate veterinary consultation. --- Proper ventilation is the single most important environmental factor in a broiler house, and exhaust fans are the engine that drives it. This guide covers how to select the right exhaust fans for your broiler house, how to size them correctly, and how to maintain them for reliable performance. It is written for broiler producers, farm managers, and poultry house technicians who want practical, actionable information they can apply to their own operations. You will learn the core principles of fan selection, the math behind fan capacity, common maintenance routines, and how to troubleshoot problems before they cost you birds. ## At a Glance - **Fan capacity is measured in cubic feet per minute (CFM)**, and your total ventilation need is based on bird weight, bird count, and outside temperature. - **Minimum ventilation fans should move 0.5 to 1.0 CFM per pound of bird weight** in cold weather to control moisture and air quality. - **Tunnel ventilation fans should provide 1.5 to 3.0 CFM per pound of bird weight** or more in hot weather to manage heat stress. - **Choose fans rated by the Air Movement and Control Association (AMCA)** or the Bioenvironmental Engineering and Technology (BET) program for verified performance data. - **Fan efficiency matters as much as raw capacity.** Look for CFM per watt ratings of 20 or higher for large tunnel fans. - **Check fan belts every 2 to 4 weeks** and replace them when they show cracks, fraying, or glazing. - **Clean fan blades and shutters monthly** during grow-out and after every flock. - **Use a manometer to check static pressure** weekly. Normal operating range is 0.05 to 0.15 inches of water for most houses. - **Keep a fan maintenance log** for every fan in the house. Record cleaning dates, belt replacements, motor checks, and any repairs. - **Call a veterinarian if you see respiratory distress, sudden death losses, or signs of ammonia toxicity** that ventilation changes do not fix within 24 hours. ## Why Exhaust Fan Selection Matters Broiler houses are enclosed environments where birds generate heat, moisture, carbon dioxide, and ammonia. Without a reliable system to remove stale air and bring in fresh air, the house quickly becomes uninhabitable. Exhaust fans do this work by pulling air out of the house, which creates a slight negative pressure that draws fresh air in through controlled inlets. The consequences of poor fan selection or maintenance are severe. Inadequate ventilation leads to wet litter, which causes footpad lesions and breast blisters. High ammonia levels damage the birds respiratory tracts and reduce feed conversion. Excess heat in summer causes panting, reduced feed intake, and in severe cases, mortality. Cold drafts in winter chill young birds and increase heating costs. Every one of these problems traces back to fans that are undersized, poorly placed, or not maintained. The goal of fan selection is to match the ventilation system to the specific house dimensions, bird density, and climate. There is no one-size-fits-all fan. A house in a hot southern climate needs more tunnel capacity than a house in a cool northern region. A house with 10,000 birds needs different airflow than one with 30,000 birds. Understanding the relationship between house size, bird weight, and airflow requirements is the foundation of good fan selection. ## Understanding Fan Capacity and Airflow Fan capacity is measured in cubic feet per minute, or CFM. This is the volume of air a fan moves at a given static pressure. Static pressure is the resistance the fan must overcome to move air. In a broiler house, static pressure is created by the inlet openings, the building structure, and the fans themselves. Think of it like drinking through a straw. A wider straw offers less resistance and lets you drink more easily. A narrower straw creates more resistance and requires more effort. Inlet openings work the same way. Wider inlets lower static pressure and let fans move more air. Narrower inlets raise static pressure and reduce fan output. Every fan has a performance curve that shows its CFM output at different static pressures. A fan rated at 20,000 CFM at 0.05 inches of static pressure might only move 15,000 CFM at 0.15 inches. Always select fans based on their performance at the static pressure you expect to operate at, not just the free air rating. Most broiler houses operate between 0.05 and 0.15 inches of static pressure, depending on the ventilation stage and inlet configuration. Fan efficiency is another critical factor. Efficiency is expressed as CFM per watt. A more efficient fan moves more air for each unit of electricity. This matters because ventilation is one of the largest energy costs in broiler production. A tunnel fan that moves 20,000 CFM at 0.10 inches of static pressure using 1,000 watts has an efficiency of 20 CFM per watt. A less efficient fan moving the same air with 1,400 watts has an efficiency of about 14 CFM per watt. Over a year of operation, the less efficient fan costs significantly more to run. When comparing fans, look for performance data that includes CFM at multiple static pressures, efficiency ratings, and noise levels. The best sources of this data are AMCA certified ratings and BET program test results. These independent testing programs verify manufacturer claims and give you reliable numbers for comparison. ## Types of Exhaust Fans for Broiler Houses Broiler houses typically use two types of exhaust fans: box fans and cone fans. Each serves a different purpose in the ventilation system. Box fans are rectangular or square fans that mount directly into the wall. They are commonly used for minimum ventilation in cold weather because they move moderate volumes of air at higher static pressures. Box fans are available in various sizes, with the most common being 24 inch, 36 inch, and 48 inch models. A 36 inch box fan typically moves 8,000 to 10,000 CFM at 0.10 inches of static pressure. A 48 inch box fan moves 15,000 to 20,000 CFM under the same conditions. Box fans are also used as stir fans inside the house to mix air and reduce temperature stratification. Cone fans, also called cone or tube axial fans, have a cone-shaped housing that directs airflow and improves efficiency. They are the standard choice for tunnel ventilation because they move very large volumes of air at lower static pressures. Cone fans are typically 48 to 54 inches in diameter and move 20,000 to 30,000 CFM at 0.10 inches of static pressure. The cone shape reduces turbulence at the fan outlet, which improves efficiency and reduces noise. These fans are usually mounted in the end wall of the house for tunnel ventilation or along the side walls for cross ventilation. Some houses also use exhaust fans with variable speed drives. These allow you to adjust fan speed and airflow to match changing conditions. Variable speed fans are useful for minimum ventilation because they can run at low speed to provide precise airflow without over ventilating. However, variable speed drives add cost and complexity. Many producers find that properly staged single speed fans work just as well at a lower initial cost. ## How to Calculate Your Fan Capacity Needs Sizing your exhaust fans correctly requires a simple calculation based on house dimensions, bird count, and target airflow rates. The process has four steps. First, calculate the total bird weight in the house. Multiply the number of birds by the average bird weight. For example, a house with 25,000 broilers averaging 4 pounds each has a total bird weight of 100,000 pounds. Second, determine your ventilation stage. Broiler houses use three main ventilation stages: minimum ventilation, transitional ventilation, and tunnel ventilation. Each stage has a target airflow rate per pound of bird weight. Minimum ventilation runs in cold weather to control moisture, ammonia, and carbon dioxide. Target airflow is 0.5 to 1.0 CFM per pound of bird weight. This is the lowest ventilation rate and runs intermittently on timers. For our example house, minimum ventilation needs 50,000 to 100,000 CFM total capacity. Transitional ventilation runs in mild weather to control temperature without using full tunnel mode. Target airflow is 1.0 to 2.0 CFM per pound of bird weight. For our example, that is 100,000 to 200,000 CFM. Tunnel ventilation runs in hot weather to create wind chill and remove heat. Target airflow is 1.5 to 3.0 CFM per pound of bird weight, with higher rates for larger birds and hotter climates. For our example, tunnel ventilation needs 150,000 to 300,000 CFM. Third, divide the total CFM needed by the CFM rating of your chosen fan to find the number of fans required. If you need 200,000 CFM for tunnel ventilation and you select a fan rated at 20,000 CFM at 0.10 inches of static pressure, you need 10 fans. Fourth, add a safety margin of 10 to 15 percent to account for fan wear, dirty blades, and static pressure variations. A house that needs 200,000 CFM should have at least 220,000 to 230,000 CFM of installed capacity. These calculations give you the total fan capacity, but you must also think about fan placement. For tunnel ventilation, fans go in the end wall opposite the tunnel inlets. The total fan area should match the inlet area for balanced airflow. For minimum ventilation, fans are spaced along the side walls to distribute airflow evenly. A common rule is to place minimum ventilation fans every 40 to 50 feet along the side wall, alternating between sides. ## Selecting the Right Fan for Your House Once you know your capacity needs, you can select specific fans. Start by choosing the fan type for each ventilation stage. Minimum ventilation fans are typically 36 to 48 inch box fans. Tunnel ventilation fans are 48 to 54 inch cone fans. You can also use large box fans for transitional ventilation, but cone fans are more efficient at moving large air volumes. Consider the climate in your region. Houses in hot climates need more tunnel capacity to handle summer heat. Houses in cold climates need reliable minimum ventilation fans that can operate at higher static pressures when inlets are restricted. A house in the southeastern United States might need 2.5 to 3.0 CFM per pound for tunnel ventilation. A house in the northern plains might need only 1.5 to 2.0 CFM per pound. Think about the age of your birds. Broilers need less ventilation early in the grow-out and much more as they grow. The system must be able to ramp up airflow as bird weight increases. This is usually handled by staging fans rather than selecting a single massive fan. Multiple smaller fans give you more control than one large fan. Look at the fan construction. The housing should be galvanized steel or another corrosion resistant material. The blade should be balanced and free of nicks or bends. The motor should be rated for continuous duty and have sealed bearings. Look for fans with shutters that open and close automatically when the fan starts and stops. Shutters prevent cold air from entering the house through idle fans in winter. Check the warranty and parts availability. A fan that cannot be repaired quickly is a liability during a heat wave. Choose fans from manufacturers with local distributors and readily available spare parts. It is also wise to keep spare motors, belts, and shutters on hand for each fan size in your house. ## Fan Placement and Airflow Distribution Fan placement is as important as fan selection. Poor placement creates dead spots where air does not move, which leads to hot zones and wet litter. Good placement creates uniform airflow that keeps all birds comfortable. For minimum ventilation, place fans in the side walls at bird height or slightly above. This puts the exhaust near the litter surface where moisture and ammonia accumulate. Space fans evenly along the wall, typically 40 to 50 feet apart. Alternate fans on opposite side walls to create good air mixing. Each minimum ventilation fan should have a corresponding inlet on the opposite wall or ceiling to ensure fresh air enters before it is exhausted. For tunnel ventilation, place fans in the end wall opposite the tunnel inlets. The fans should be spread across the full width of the end wall, not clustered in the center. This creates a uniform curtain of air moving down the length of the house. The tunnel inlets at the opposite end should be sized to match the total fan capacity. A common guideline is to provide 1 square foot of inlet area for every 500 to 600 CFM of fan capacity. For transitional ventilation, use a combination of side wall fans and tunnel fans. The goal is to move more air than minimum ventilation but less than full tunnel mode. This can be achieved by running a few tunnel fans along with side wall fans, or by using variable speed fans to modulate airflow. Pay attention to the air inlet system. Exhaust fans only work well if fresh air can enter the house through controlled inlets. If inlets are too small, static pressure rises and fan output drops. If inlets are too large, air enters at high velocity and creates drafts. Work with your inlet supplier or extension agent to set up a properly matched inlet system for your fan capacity. ## Minimum Ventilation Fan Control Minimum ventilation is the most challenging stage to manage because it runs on timers and must be adjusted frequently. The goal is to remove moisture and gases while retaining heat. Running minimum ventilation fans too much wastes heat and chills birds. Running them too little allows ammonia and moisture to build up. Minimum ventilation fans run intermittently on a timer cycle. A typical cycle might be 5 minutes on, 10 minutes off, repeated continuously. The timer settings depend on bird age, bird weight, outside temperature, and litter condition. Start with a low timer setting and increase it gradually as the flock grows. The key indicator for minimum ventilation is relative humidity. Aim for 50 to 70 percent relative humidity in the house. If humidity stays above 70 percent, increase ventilation time. If it drops below 50 percent, decrease ventilation time. Ammonia levels are another indicator. Keep ammonia below 25 parts per million at bird level. If you can smell ammonia, it is too high and you need more ventilation. Use a controller to automate minimum ventilation. Modern controllers can adjust timer settings based on outside temperature, house temperature, humidity, and bird age. They can also stage fans so that fans run in sequence rather than all at once. This provides more even airflow and reduces wear on individual fans. ## Tunnel Ventilation Management Tunnel ventilation is the highest capacity ventilation stage and is used to manage heat stress in warm weather. The goal is to create a wind chill effect that helps birds shed heat. Air speed at bird level should be 400 to 700 feet per minute, with higher speeds for larger birds and hotter conditions. To achieve this air speed, all tunnel fans run at full capacity and tunnel inlets are fully open. The house becomes a wind tunnel with air moving from the inlet end to the fan end. This creates a temperature gradient along the house, with the coolest air at the inlet end and the warmest air at the fan end. The temperature difference between the ends should be no more than 5 to 8 degrees Fahrenheit in a well designed system. Tunnel ventilation works best with evaporative cooling pads at the inlet end. The pads cool incoming air by evaporation, which can reduce air temperature by 10 to 20 degrees Fahrenheit in dry climates. Pads are less effective in humid climates where the air is already saturated. Even without pads, tunnel ventilation provides significant cooling through wind chill. Run tunnel ventilation when house temperature exceeds the upper set point for the birds age. For broilers, this is typically around 80 to 85 degrees Fahrenheit, depending on bird age and acclimation. Start tunnel fans gradually as temperature rises, and bring on additional fans as needed to hold temperature. ## Common Fan Selection Mistakes Many producers make the same mistakes when selecting fans for their broiler houses. Recognizing these mistakes can save you money and prevent performance problems. Selecting fans based on free air rating instead of performance at operating static pressure is a common error. A fan that moves 25,000 CFM in free air might move only 18,000 CFM at 0.15 inches of static pressure. Always use the performance data at the static pressure you expect to operate at. Undersizing the ventilation system is another frequent mistake. Producers often try to save money by installing fewer fans than needed. This leads to inadequate airflow in hot weather and causes heat stress, reduced feed intake, and mortality. The cost of lost production far exceeds the savings from buying fewer fans. Ignoring fan efficiency is also common. Two fans with the same CFM rating can have very different energy consumption. A fan that uses 30 percent more electricity to move the same air costs thousands of dollars more over its lifetime. Compare CFM per watt ratings and choose the most efficient fan that fits your budget. Poor fan placement creates airflow problems that no amount of fan capacity can fix. Clustering fans in one area leaves other areas with poor airflow. Not matching inlet area to fan capacity creates high static pressure and reduced fan output. Take the time to design the fan and inlet layout properly. ## Fan Maintenance Schedule Regular maintenance keeps fans performing at their rated capacity. A dirty fan can lose 20 to 30 percent of its airflow. A worn belt can slip and reduce fan speed. A failing motor can stop a fan entirely at the worst possible time. Establish a maintenance schedule and stick to it. The schedule below is a practical starting point, but adjust it based on your house conditions and manufacturer recommendations. ### Weekly Maintenance Check fan belts for tension and condition. A properly tensioned belt deflects about one half inch when pressed firmly at the midpoint between pulleys. Replace belts that are cracked, frayed, glazed, or stretched. Check shutters for free operation. They should open fully when the fan runs and close tightly when it stops. Look for debris on fan blades and clean as needed. Listen for unusual noises from motors or bearings. Check that all fans come on when called by the controller. ### Monthly Maintenance Clean fan blades and shutters with a mild detergent and water. Remove built up dust and dirt that reduces airflow. Check and tighten all mounting bolts and electrical connections. Lubricate motor bearings if they have grease fittings. Check fan guards and safety screens for damage. Inspect fan belts for wear and replace if needed. Check the condition of fan housings for rust or corrosion. ### Between Flocks Perform a thorough cleaning of all fans. Remove shutters and clean them separately. Wash blades with a pressure washer if needed. Check and replace belts that show any signs of wear. Test all fans to confirm they operate at full speed. Check the operation of the controller and its sensors. Inspect wiring for damage from rodents or moisture. Replace any worn or damaged parts before the next flock starts. ### Annual Maintenance Have a qualified electrician inspect all fan motors and electrical systems. Check motor bearings and replace if worn. Verify that all fans meet their rated performance using a flow hood or anemometer. Inspect fan housings for structural damage and repair as needed. Check the building structure around fans for air leaks that reduce efficiency. Consider replacing fans that are more than 10 to 15 years old if they have lost significant capacity. ## Monitoring Fan Performance You cannot manage what you do not measure. Monitoring fan performance helps you catch problems early and maintain optimal ventilation. Use a manometer or static pressure gauge to check static pressure regularly. The gauge should be mounted where you can read it easily. Compare the reading to the expected range for your ventilation stage. If static pressure is higher than expected, check for blocked inlets or dirty fans. If it is lower than expected, check for air leaks or open doors. Measure actual fan output with a flow hood or anemometer. A flow hood fits over the fan outlet and measures the volume of air moving through it. An anemometer measures air speed at a point. Use these tools to verify that each fan meets its rated performance. Compare readings to the baseline you established when the fans were new. A fan that has lost 15 percent or more of its output needs attention. Monitor the temperature gradient along the house during tunnel ventilation. Use temperature sensors at the inlet end, middle, and fan end. A gradient of more than 8 degrees Fahrenheit indicates poor airflow distribution or insufficient fan capacity. Investigate and correct the cause. Track energy use per flock. A sudden increase in electricity use per pound of bird produced can indicate fan problems or controller issues. Compare energy use between flocks to identify trends. ## Recordkeeping for Fan Maintenance Keep a maintenance log for each fan in the house. The log should include the fan identification number, make and model, installation date, and maintenance history. Record every cleaning, belt replacement, motor repair, and performance test. This information helps you schedule maintenance, identify recurring problems, and make replacement decisions. A simple spreadsheet works well for recordkeeping. Create a row for each fan and columns for maintenance dates and activities. Update the log every time you work on a fan. Review the log between flocks to identify fans that need extra attention. Also keep records of controller settings and ventilation changes. Note the timer settings for minimum ventilation, the temperature set points for each stage, and any adjustments you make during the flock. This information helps you refine your ventilation strategy over time. ## Troubleshooting Common Fan Problems Even with good maintenance, fans can fail. Knowing how to diagnose common problems saves time and prevents prolonged ventilation outages. A fan that runs slowly or does not reach full speed may have a worn belt, a failing motor, or an electrical problem. Check the belt first. A slipping belt is the most common cause of reduced fan speed. If the belt is tight and in good condition, check the motor and electrical connections. A fan that makes unusual noise may have a worn bearing, an unbalanced blade, or debris in the housing. Stop the fan and inspect it carefully. Clean any debris and check the blade for damage. If the noise persists, the bearing or motor may need replacement. A fan that does not start may have a tripped breaker, a blown fuse, a failed motor, or a problem with the controller. Check the electrical supply first. If power is present, check the motor. A failed capacitor is a common cause of motor failure in single phase fans. A fan that runs but moves little air may have dirty blades, a blocked inlet, or a closed shutter. Check the shutter operation first. A shutter that does not open fully can reduce airflow by 50 percent or more. Clean the blades and check the inlet system. A fan that cycles on and off frequently may be controlled by a faulty sensor or have a problem with the controller. Check the controller settings and sensor operation. Frequent cycling increases wear on the fan and reduces its lifespan. ## When to Call a Professional Most fan maintenance and troubleshooting can be done by farm staff with basic mechanical skills. However, some situations require professional help. Call an electrician if you see signs of electrical problems such as tripped breakers, burning smells, or damaged wiring. Electrical work is dangerous and should only be done by qualified professionals. Call a ventilation specialist if you cannot achieve adequate airflow despite having the correct number of fans. The problem may be in the inlet system, the building structure, or the controller. A specialist can perform a complete ventilation audit and recommend corrective measures. Call your extension agent if you need help calculating fan capacity or designing a ventilation system. Extension agents have access to resources and expertise that can save you money and prevent costly mistakes. Call a veterinarian if you see signs of respiratory distress, increased mortality, or other health problems that you suspect are related to ventilation. Poor ventilation can cause or worsen respiratory disease. A veterinarian can help you diagnose the problem and recommend treatment. ## Ventilation and Bird Health The connection between ventilation and bird health is direct and well established. Poor ventilation leads to high ammonia, high humidity, and poor air quality. These conditions damage the respiratory tract and make birds more susceptible to disease. Ammonia is a particular concern. Ammonia is produced by bacterial breakdown of uric acid in the litter. At concentrations above 25 parts per million, ammonia damages the cilia in the respiratory tract. These tiny hair like structures help clear mucus and pathogens from the airways. When they are damaged, bacteria and viruses can establish infections more easily. Birds exposed to high ammonia have poorer feed conversion, lower weight gain, and higher mortality. Carbon dioxide is another concern. High carbon dioxide levels indicate inadequate ventilation and can cause drowsiness, reduced feed intake, and poor growth. Carbon dioxide levels above 3,000 parts per million are a sign that ventilation is insufficient. Relative humidity is closely tied to ventilation and litter quality. High humidity leads to wet litter, which increases ammonia production and causes footpad lesions. Low humidity leads to dusty conditions and respiratory irritation. Maintaining relative humidity between 50 and 70 percent is the goal. Ventilation also plays a role in disease prevention. Good airflow reduces the concentration of airborne pathogens and helps keep litter dry. Dry litter supports a healthier microbial balance and reduces the risk of disease. During disease outbreaks, increasing ventilation can help reduce pathogen load in the house. If you see signs of respiratory disease such as coughing, sneezing, or nasal discharge, check ventilation first. Increase ventilation to improve air quality and reduce pathogen load. If signs persist for more than 24 hours, call a veterinarian. ## Energy Efficiency and Cost Considerations Ventilation is one of the largest energy costs in broiler production. Fans run continuously in hot weather and intermittently in cold weather. Over a year, a broiler house can consume thousands of kilowatt hours of electricity for ventilation alone. Fan efficiency is the biggest factor in energy cost. A fan that moves 20,000 CFM at 20 CFM per watt uses 1,000 watts. A fan that moves the same air at 14 CFM per watt uses 1,429 watts. Over 2,000 hours of operation, the less efficient fan uses an extra 858 kilowatt hours. At 12 cents per kilowatt hour, that is an extra 103 dollars per fan per year. A house with 10 tunnel fans would save over 1,000 dollars per year by choosing the more efficient fans. Proper maintenance also saves energy. A dirty fan blade can reduce airflow by 20 to 30 percent. A fan that is moving less air must run longer to provide the same ventilation. This increases energy use and reduces bird performance. Consider using variable speed drives for minimum ventilation fans. Running a fan at half speed uses about one eighth the energy of running it at full speed. This can provide significant energy savings during periods when full airflow is not needed. Look for energy rebates from your utility company. Many utilities offer incentives for installing energy efficient fans and controllers. Check with your local utility to see what programs are available. ## Choosing Between New Fans and Repairs Fans have a finite lifespan. A well maintained fan can last 10 to 15 years, but performance declines over time. Belts wear, bearings fail, blades corrode, and motors lose efficiency. At some point, it costs more to keep an old fan running than to replace it. Consider replacing a fan when it has lost more than 20 percent of its rated airflow and cannot be restored to full performance with maintenance. Consider replacement when repair costs exceed 50 percent of the cost of a new fan. Consider replacement when the fan is more than 10 years old and replacement parts are hard to find. When replacing fans, consider upgrading to more efficient models. The energy savings from a new high efficiency fan can offset the purchase price over a few years. Compare the total cost of ownership, including purchase price, installation, energy use, and maintenance, when making replacement decisions. ## Preparing for Extreme Weather Extreme weather events put extra stress on ventilation systems. Heat waves require maximum tunnel ventilation. Cold snaps require reliable minimum ventilation. Power outages can stop all fans and cause catastrophic losses. Have a plan for heat waves. Check all tunnel fans before hot weather arrives. Clean blades and shutters, replace worn belts, and test all fans. Verify that evaporative cooling pads are in good condition and have adequate water supply. Have a backup generator ready and test it before the heat arrives. Have a plan for cold weather. Check minimum ventilation fans and timers before cold weather arrives. Verify that inlets operate correctly and provide proper air distribution. Check the heating system to ensure it can maintain temperature when ventilation is running. Have a backup power plan. A power outage during hot weather can kill birds within minutes. A generator that automatically starts when power fails is the best protection. If you do not have an automatic generator, have a portable generator and a plan to connect it quickly. Keep fuel on hand and test the generator regularly. ## Frequently Asked Questions **How do I know how many exhaust fans I need for my broiler house?** Calculate the total bird weight in the house by multiplying bird count by average bird weight. Then multiply that number by the target CFM per pound for your ventilation stage. For tunnel ventilation, use 1.5 to 3.0 CFM per pound depending on climate and bird size. Divide the total CFM by the rated CFM of your chosen fan at operating static pressure. Add a 10 to 15 percent safety margin. For example, a house with 25,000 birds at 4 pounds each has 100,000 pounds of bird weight. At 2.0 CFM per pound, you need 200,000 CFM. With fans rated at 20,000 CFM, you need 10 fans, plus 1 to 2 extra for safety margin. **What is the difference between minimum ventilation and tunnel ventilation fans?** Minimum ventilation fans are typically smaller box fans mounted in the side walls. They run intermittently on timers to control moisture and air quality in cold weather. Tunnel ventilation fans are large cone fans mounted in the end wall. They run continuously in hot weather to create wind chill and remove heat. Minimum ventilation fans operate at higher static pressures and move moderate air volumes. Tunnel fans operate at lower static pressures and move very large air volumes. **How often should I clean my exhaust fan blades?** Clean fan blades at least monthly during grow-out and thoroughly between flocks. Dirty blades can reduce airflow by 20 to 30 percent. In dusty conditions or during winter when fans run less often, check blades every 2 weeks. Use a mild detergent and water to remove dust and grime. Do not use harsh chemicals that can damage the blade finish. **What static pressure should my broiler house operate at?** Most broiler houses operate between 0.05 and 0.15 inches of static pressure. Minimum ventilation often runs at 0.08 to 0.12 inches. Tunnel ventilation runs at 0.05 to 0.10 inches. The exact pressure depends on your inlet system and house design. Check with your ventilation controller manufacturer or extension agent for the recommended range for your specific house. **How do I know if my fan belts need replacement?** Check fan belts every 2 to 4 weeks. Replace belts that show cracks, fraying, glazing, or stretching. A properly tensioned belt deflects about one half inch when pressed firmly at the midpoint between pulleys. If the belt is loose and slips, it will reduce fan speed and airflow. Replace belts in pairs if you have a dual belt system. Keep spare belts on hand for each fan size in your house. **What should I do if ammonia levels stay high even with maximum ventilation?** First check that all fans are operating at full capacity. Clean dirty blades and replace worn belts. Check that inlets are open and providing fresh air. If ammonia remains above 25 parts per million, the problem may be wet litter. High moisture in litter increases ammonia production. Work to dry the litter by increasing ventilation and addressing any water leaks. If ammonia levels remain high despite these measures, call your extension agent or veterinarian for assistance. **Can I use the same fans for minimum and tunnel ventilation?** Some houses use large fans that serve both purposes, but this is not ideal. Large tunnel fans move too much air for minimum ventilation and cannot be throttled down easily without variable speed drives. Small minimum ventilation fans do not move enough air for tunnel ventilation. The best system uses dedicated fans for each stage. This gives you precise control and better energy efficiency. **How long should broiler house exhaust fans last?** With proper maintenance, exhaust fans can last 10 to 15 years. However, performance declines over time. Belts wear, bearings fail, and blades corrode. Monitor fan output regularly and replace fans that have lost more than 20 percent of their rated airflow. Consider replacing fans that are more than 10 years old if repair costs are high or replacement parts are hard to find. ## Related Farming Guides This section will be populated with related guides on [poultry house management](/knowledge/animal-farming/poultry/poultry-house-management-ventilation-lighting-and-biosecurity-integration), ventilation systems, and broiler production practices. Check back for updated links to complementary resources. ## Related Clinical & Scientific Guides * [Poultry Farm Fencing: Materials, Design, and Predator Exclusion](/knowledge/animal-farming/poultry/poultry-farm-fencing-materials-design-predator-exclusion) * [Broiler House Wind Speed and Airflow Measurement](/knowledge/animal-farming/poultry/broiler-house-wind-speed-airflow-measurement) * [Broiler House Heating Systems: Types and Efficiency](/knowledge/animal-farming/poultry/broiler-house-heating-systems-types-efficiency) ## References - [FAO Poultry Production](https://www.fao.org/poultry-production-products/en/) - [USDA APHIS Poultry Health](https://www.aphis.usda.gov/livestock-poultry-disease/avian) - [WOAH Avian Influenza](https://www.woah.org/en/disease/avian-influenza/) - [FAO Animal Production and Health](https://www.fao.org/animal-production/en/) - [WOAH (World Organisation for Animal Health)](https://www.woah.org/en/home/) > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.