Shed Ventilation & Airflow & Fans Done Right

Animals constantly give off heat, moisture, CO₂ and ammonia from manure, and bedding adds dust. Without enough fresh air this builds up, raising temperature and humidity and harming health, growth and milk or egg output. Ventilation flushes stale air out and brings cool, dry air in, keeping dairy, poultry and pig sheds healthy and productive.

Required airflow = shed volume × air changes per hour (ACH). Shed volume = length × width × height. So a 30 × 12 × 4 m shed is 1440 m³; at 40 air changes per hour it needs 1440 × 40 = 57,600 m³/h of airflow. That airflow is then divided by each fan's capacity to find how many exhaust fans you need.

ACH is how many times the entire air volume of the shed is replaced in one hour. Cold-weather or minimum ventilation may be just a few changes per hour to control moisture; hot-weather tunnel ventilation for poultry can be 40–60+ ACH to remove heat. Pick the ACH that matches your species, season and climate.

Divide the required airflow by the rated capacity of one fan, then round up. If the shed needs 57,600 m³/h and each fan moves 20,000 m³/h, you need 57,600 ÷ 20,000 = 2.9, rounded up to 3 fans. Always round up so you meet or exceed the target, and check fan capacity at the static pressure of your shed.

Both measure airflow. m³/h is cubic metres per hour (metric); CFM is cubic feet per minute (imperial), common on fan spec sheets. 1 m³/h ≈ 0.589 CFM, or 1 CFM ≈ 1.699 m³/h. This tool shows both so you can match the airflow target to whichever units your fans are rated in.

Yes. Hot, humid climates need much higher ACH to strip heat and moisture, while cool climates may only need minimum ventilation to control humidity and ammonia. The same shed can need very different fan numbers in summer versus winter — size for the peak hot-weather load and run fewer fans when it's cool.

The principle is identical — volume × ACH — but the rates differ. Broiler houses use high tunnel airflow for heat; dairy sheds focus on air speed over cows and moisture removal; pig sheds balance temperature with draught control over young stock. Set the ACH to your species and stage, and the maths handles the rest.

The calculator sizes mechanical (fan) ventilation. Naturally ventilated sheds rely on ridge and side openings sized to wind and stack effect, which depends on the building layout. You can still use the required airflow figure as a target to check whether your openings are likely adequate, or as a basis for adding fans.

Enter the shed length, width and height in the units the tool offers; it computes the volume and the airflow target for you. Just make sure all three dimensions are in the same units and that the fan capacity you enter is in m³/h or CFM consistently — the tool reports both.

They're solid planning figures. Real performance depends on fan efficiency at your shed's static pressure, inlet area, leakage, and how evenly air moves through the building. Use the result to size and lay out fans, then verify with a smoke test or anemometer and adjust — ventilation design is about steering, not exact prediction.