How to decide blower capacity?

Deciding blower capacity for an air mover or fan requires considering the area size, the severity of drying needed, and the desired air changes. Blower capacity is measured in CFM, cubic feet per minute, and also by velocity. For general ventilation, a good rule is you want enough CFM to provide 6 to 10 air changes per hour in the space. To calculate, multiply room volume in cubic feet by desired air changes and divide by 60. For example, a 1000 square foot room with 8 foot ceilings is 8000 cubic feet, for 6 air changes per hour you need 800 CFM, but for rapid drying you need much more. For water damage drying, IICRC standards recommend one air mover per 150 to 300 square feet, which typically means 2500 to 4000 CFM per 300 square feet. For light drying like after carpet cleaning, 1500 to 2500 CFM is sufficient. For heavy saturation with hardwood or plaster, you need higher capacity at 4000 to 6000 CFM per area or multiple units. Also consider static pressure if pushing air through ducts, and amp draw to avoid tripping breakers. For cooling a workshop, choose higher CFM for more wind chill, around 3000 CFM per 400 square feet. For home use, a mid-size 1/2 horsepower unit around 3000 CFM is versatile. Always choose slightly more capacity than minimum to ensure fast drying and prevent mold within 24 to 48 hours.