The short answer: size fans for your summer maximum temperature, size inlets for your winter minimum, and put the inlet above the lying area so fresh air mixes before it reaches pig height.
1. Air rates you can actually use
Two figures decide the whole system. Minimum ventilation, used in winter, is roughly 3–5 m³ per hour per kg of pig weight — it exists to remove moisture and ammonia, not to cool. Maximum ventilation, used in summer, is roughly 60–100 m³ per hour per pig in a temperate climate, rising above 150 m³/h in hot regions. Size the fan bank for the maximum and the inlets for the minimum, never the other way round.
| Stage | Pig stage | Minimum (winter) | Maximum (summer) |
|---|---|---|---|
| Piglet / weaner | 6–30 kg | 3 m³/h per kg | 30–60 m³/h per pig |
| Grower | 30–60 kg | 4 m³/h per kg | 60–90 m³/h per pig |
| Finisher / sow | 60 kg+ | 5 m³/h per kg | 90–150 m³/h per pig |
2. Fans: cone, drive and staging
A pig house ventilation system is almost never one big fan. It is a bank of fans in stages: stage 1 on variable speed for winter minimum, then additional fans switched on as temperature rises. A cone exhaust fan of the same diameter moves 15–20 % more air than a fan without a cone, so cones are usually the cheapest way to gain capacity. Belt drive is quieter and easy to speed-tune; direct drive needs no belt maintenance and is the better choice for continuous winter duty.
3. Inlets decide whether it works
The most common failure is not fan capacity, it is inlet position. Incoming cold air must be directed along the ceiling, mix with room air and then descend slowly. If the inlet is at pig height you get a draught, and a draught causes more respiratory disease than any other single factor. Put inlets above the lying area, use a drop ceiling to form a mixing zone, and adjust them as pigs grow — a small detail that is often forgotten after commissioning.
4. Cooling in hot climates
Above roughly 26 °C, pigs reduce feed intake and daily gain falls. Evaporative cooling pads drop inlet air temperature by 5–12 °C depending on relative humidity: allow about 1 m² of pad per 20,000–25,000 m³/h of airflow and never try to cool below the wet-bulb temperature of your site. In dry climates pads are extremely effective; in humid climates, high-velocity tunnel ventilation with increased air speed gives better results than a big pad.
5. Controls and alarms
A controller should run a temperature curve rather than a single set point, operate variable-speed on the first stage, and — critically — include an alarm output. A ventilation failure on a hot day or a cold night kills pigs faster than any disease. Test the alarm once a month.
Conclusion
Size for summer, control for winter, and place inlets above the pigs. If you send us your house dimensions, pig weights and local min/max temperatures, we will calculate the fan, inlet and cooling pad sizing for your building rather than selling you a standard package.