Fan quantity comes from required airflow. Cooling-pad area comes from the same airflow—not from bird number alone.
For an H-type layer cage house, the correct number of exhaust fans and the required cooling-pad area depend on house cross-section, target air velocity, actual fan performance at operating static pressure, cage density, inlet resistance and local temperature/humidity.
The calculation should therefore move in one direction: House → Air Velocity → Total Airflow → Fan Selection → Cooling Pad Area → Field Verification.
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Direct Answer
Do not ask “How many fans for 30,000 layers?” first.
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First calculate the airflow the building needs to achieve the selected hot-weather air speed. Then divide that airflow by the certified fan capacity at the expected static pressure. After fan airflow is established, size cooling-pad area from an acceptable pad-face velocity. |
2. Fan Quantity = Required Airflow ÷ Fan Airflow at Operating Static Pressure
3. Cooling Pad Area = Required Airflow ÷ Design Pad-Face Velocity
What information is needed to calculate fans and cooling pads?
Fan quantity is a result of the completed house and layer cage design. Missing one of the following inputs can make a neat-looking calculation unreliable.
| Input | Why it matters |
| House width & effective height | Together they define the effective air-moving cross-section used in the screening calculation. |
| House length | Affects pressure loss, tunnel performance and the time air spends moving through the house. |
| H-type rows & tiers | Change bird heat load and airflow resistance through the occupied cage zone. |
| Target hot-weather air speed | Turns cross-sectional area into required airflow. |
| Fan curve / certified airflow | Fan airflow falls as static pressure increases; nominal fan diameter is not enough. |
| Cooling-pad specification | Pad thickness, material and manufacturer design velocity determine required area. |
| Peak temperature & RH | Determine whether evaporative cooling is useful and how aggressively it should operate. |
How does house size become an airflow requirement?
A is the effective cross-sectional area through which tunnel air must move. V is the selected target average air velocity for the design condition.
Why should fan quantity use airflow at static pressure?
Because an exhaust fan does not move its free-air rating once it is pulling through cooling pads, inlets, shutters and a long poultry house. Static pressure reduces delivered airflow.
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Correct Input
Fan airflow at expected operating static pressure |
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Not Enough
“50-inch fan” or “1,400 mm fan” alone |
Round up to a whole fan, then check whether the design needs practical reserve capacity for dirty shutters/pads, belt wear, fan aging or extreme-weather operation. The reserve should be an engineering decision, not an arbitrary fixed percentage.
What raises static pressure in an H-type layer house?
| Cooling padsWet or dirty pads increase resistance compared with an open inlet. | Inlet restrictionUndersized doors, curtains or openings can limit airflow. | Fan accessoriesShutters, guards and cones affect delivered airflow. |
| House leakageUncontrolled air can bypass the intended cooling-pad path. | Cage / equipment layoutRows, tiers and equipment can affect distribution through the occupied zone. | Maintenance conditionDust, slipping belts and damaged shutters reduce real fan performance. |
Mississippi State Extension recommends selecting poultry fans from independently rated performance data at relevant static pressure rather than free-air capacity. This is especially important once cooling pads and shutters are part of the system.
How much evaporative cooling-pad area is needed?
Once the fan system’s design airflow is known, calculate pad area from the allowable air speed through the selected pad.
Mississippi State Extension describes around 350 ft/min (about 1.78 m/s) as a typical design velocity for air entering evaporative pads, while also noting that actual pad velocities can vary considerably by system. Use the pad manufacturer’s specification for final design.
What does the calculation look like in practice?
The example below is deliberately hypothetical. It shows the arithmetic only; it is not a LIVI quotation or a final ventilation design.
| Example input | Illustrative value |
| Effective air-moving cross-section | 60 m² |
| Screening target air velocity | 2.0 m/s |
| Required airflow | 60 × 2.0 × 3,600 = 432,000 m³/h |
| Example fan capacity at design static pressure | 40,000 m³/h per fan |
| Basic arithmetic fan count | 432,000 ÷ 40,000 = 10.8 → 11 fans minimum by arithmetic |
| Example pad-face velocity | 1.78 m/s |
| Basic pad-area screening | 120 m³/s ÷ 1.78 ≈ 67.4 m² |
Do 4-tier and 5-tier layer cage houses use the same fan calculation?
The airflow equation is the same, but the engineering inputs and field verification can change. Higher tier count changes bird density, vertical heat distribution and airflow through the occupied cage zone.
| 4-Tier H-TypeCheck total bird load, cage-row resistance and air velocity across lower/middle/upper levels. | 5-Tier H-TypeHigher vertical density increases the importance of clear height, upper-tier air movement and uniformity testing. |
See 4-Tier vs 5-Tier H-Type Layer Cages for the broader layout decision. Also confirm the final number of rows using the H-type cage row calculation guide before the ventilation system is frozen.
How should the calculated pad area be arranged?
Check inlet opening behind/in front of the pad. Curtains, doors or framing must not become the real restriction.
Check pad height and available wall length. Required area must physically fit the house.
Check water distribution. Pads need uniform wetting, pump capacity and make-up water.
Check climate. Hot-dry climates benefit more from evaporative cooling than hot-humid conditions.
LIVI’s poultry environmental control system includes ventilation fans and cooling-pad equipment; final quantity should be tied to the project calculation rather than purchased as isolated accessories.
What should be measured after the fans and pads are installed?
A correct spreadsheet can still produce poor bird-level conditions if installation or maintenance changes the real airflow.
| ✓ Full-tunnel static pressure | ✓ Average house air speed |
| ✓ Upper / middle / lower tier air movement | ✓ Pad-end to fan-end temperature difference |
| ✓ Uniform pad wetting | ✓ Tunnel doors / inlets fully open |
| ✓ Fan shutter and belt condition | ✓ Uncontrolled air leakage |
| ✓ Generator / alarm operation | ✓ Re-test with birds stocked |
What causes fan and cooling-pad calculations to fail?
2. Using free-air fan capacity instead of airflow at operating static pressure.
3. Adding fans without increasing restricted pad/inlet area.
4. Copying fan quantities from another H-type project with different house dimensions.
5. Never measuring actual air speed and static pressure after installation.
Send these data for a real fan / cooling-pad calculation
✓ Peak summer temperature
✓ Peak / typical relative humidity
✓ House length × internal width × clear/effective height
✓ H-type cage model
✓ Number of rows
✓ 4-tier or 5-tier layout
✓ Total bird capacity per house
✓ Fan model or proposed fan performance data
✓ Cooling-pad specification
✓ Voltage / frequency
✓ Water source and backup power
Exhaust fan and cooling-pad sizing questions
How many exhaust fans are needed for a 20,000- or 30,000-layer H-type house?
Bird capacity alone is not enough. Calculate required airflow from the effective cross-sectional area and target air speed, then divide by the selected fan’s certified airflow at the expected static pressure.
Can I calculate fan quantity from fan diameter?
No. Two fans with the same nominal diameter can deliver different airflow and efficiency, especially when static pressure rises.
What cooling-pad face velocity should I use?
Use the pad manufacturer’s engineering value. Around 350 ft/min (about 1.78 m/s) is a common published reference for evaporative pads, but it is not a universal value for every pad product.
Will adding more fans always increase house air speed?
Not proportionally. If pad area, inlet opening or other restrictions are too small, static pressure rises and each fan can deliver less airflow.
Should a 5-tier house automatically use more fans than a 4-tier house?
Not by a fixed fan-per-tier rule. Recalculate the completed house because bird density, cross-section, cage resistance and required bird-level air movement can all change.
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Fan & Cooling Pad Calculation
Send the house and climate dataLIVI can coordinate the H-type cage layout, airflow requirement, fan selection and cooling-pad configuration for the project. |