Very important to avoid Co2 accumulation during brooding

Ashra Ali Qureshi Dear sir, how can I feel birds are feeling CO2 without any CO2 detector?

Aziz Sacranie O2 and CO2 will always be correlated. If CO2 is high O2 must be low and vice versa. Measuring O2 is complicated/expensive if you want a reasonable accuracy. CO2 is easier/cheaper and more accurate. The resolution on a CO2 sensor, measuring in ppm, is higher (same price level) than an O2 sensor.
Air change every 5 minutes. I guess this recommendation will depend on age of the birds. Let's say we have a house of 2,000 sqm, 3 meters average height = 6,000 m3. Air exchange every 5 minutes equals 72,000 m3 per hour. If you have placed 35,000 chicks this will be your minimum ventilation pr kg live weight:
Day 0: 49 m3/kg/h
Day 7: 11 m3/kg/h
Day 14: 4,2 m3/kg/h

Day 35: 0,9

Ventilating 11 m3/kg/h will require a significant heat capacity, depending on the outside temperature. But since outside temperature does not influence CO2 level in the house, you could need a heat capacity of 2-3 MW or more.
CO2 comes from the birds, and open combustion heating systems. Recommendations for minimum ventilation must be based on number of birds and heating system more than air exchange. If based on air exchange, you must ventilate the same if you have placed 22 birds per sqm as 10.

Another recommendation is to ventilate 1 m3/h kg per kg live weight. Even better to ventilate 1 m3 per kg metabolic weight (live weight^0,75)