A 4,000-British-thermal-unit portable air conditioner is used to cool rooms that measure less than 100 square feet, like small bedrooms or home offices. While these air conditioners can be moved, they require some form of ventilation system to properly cool the coil and transfer hot air outdoors.
Ventilation kits are available for different types of windows, sliding doors and as drop-ceiling kits for rooms without windows. Manufacturers recommend increasing the amount of Btu by 600 for rooms with more than one occupant. For rooms with high ceilings and homes located in warmer climates, increase Btu by 10 to 20 percent to ensure adequate cooling. If a portable air conditioner is too small, it runs continuously. If it is too large, it cycles off before the room is properly cooled.