Which kind of cooling suits the space
A fan cools people, not the room, while an evaporative cooler takes a few degrees off in dry weather but needs fresh air flowing through. An air conditioner pulls heat and moisture out and sends them outside, so it works in any weather but needs a way to get rid of that heat: a hose through a window, two holes in a wall or an outdoor unit. Air curtains help keep warm or cool air inside while a door stays open.
Sizing by cooling power and airflow
Air conditioners are sized by cooling power, in BTU (British Thermal Units) or kW (kilowatts), and 1 kW is roughly 3,400 BTU. As a rough guide, a bedroom needs about 2 kW (7000 BTU), a living room about 3.5 kW (12000 BTU) and a large open plan room or office 5 kW and above, with more for big windows, people and computers. Fans and evaporative coolers are sized by airflow instead, in cubic metres of air an hour.
Plug in, two holes or an installer
Most portable air conditioners, evaporative coolers and fans plug into an ordinary socket with no installation. An all-in-one needs two holes cored through an outside wall, while split systems and cassettes need refrigerant pipework connected by an F-Gas registered installer, and often a dedicated circuit fitted by a qualified electrician. Running costs follow power use, from a few watts for a fan to around a kilowatt for an air conditioner, and split systems give far more cooling per unit of electricity than portable ones.
