A portable air conditioner is one on wheels that can be easily transported inside a home or office. They are currently available with capacities of about 5,000–60,000 BTU/h (1,800–18,000 W output) and with and without electric-resistance heaters. Portable air conditioners are either evaporative or refrigerative.
 
Portable refrigerative air conditioners come in two forms, split and hose. These compressor-based refrigerant systems are air-cooled, meaning they use air to exchange heat, in the same way as a car or typical household air conditioner does. Such a system dehumidifies the air as it cools it. It collects water condensed from the cooled air and produces hot air which must be vented outside the cooled area; doing so transfers heat from the air in the cooled area to the outside air.
 
A portable split system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit.
 
Hose systems, which can be monoblock or air-to-air, are vented to the outside via air ducts. The monoblock type collects the water in a bucket or tray and stops when full. The air-to-air type re-evaporates the water and discharges it through the ducted hose and can run continuously.
 
A single-duct unit uses air from within the room to cool its condenser, and then vents it outside. This air is replaced by hot air from outside or other rooms, thus reducing the unit's effectiveness. Modern units might have a coefficient of performance (COP, sometimes called "efficiency") of approximately 3 (i.e., 1 kW of electricity will produce 3 kW of cooling). A dual-duct unit draws air to cool its condenser from outside instead of from inside the room, and thus is more effective than most single-duct units.
 
Evaporative air coolers, sometimes called "swamp coolers", do not have a compressor or condenser. Liquid water is evaporated on the cooling fins, releasing the vapour into the cooled area. Evaporating water absorbs a significant amount of heat, the latent heat of vaporisation, cooling the air: humans and other animals use the same mechanism to cool themselves by sweating. They have the advantage of needing no hoses to vent heat outside the cooled area, making them truly portable; and they are very cheap to install and use less energy than refrigerative air conditioners. Disadvantages are that unless ambient humidity is low (as in a dry climate) cooling is limited and the cooled air is very humid and can feel clammy. Also, they use a lot of water, which is often at a premium in the dry climates where they work best.
 
A typical single hosed portable air conditioner can cool a room that is 475 sq ft (44.1 m2) or smaller and has at most a cooling power of 15,000 BTUs/h (4.3 kW). However, single hosed units cool a room less effectively than dual hosed as the air expelled from the room through the single hose creates negative pressure inside the room. Because of this, air (potentially warm air) from neighboring rooms is pulled into the room with the cooling unit to compensate.[25]