Window room air conditioner is installed as a primary source of cool air in the room or as an addition to the central AC system. These units are made for three different window types: standard, slider and casement. This air conditioner takes hot air from the room, cools and dehumidifies and returns it back inside. This is the most popular air conditioner type. Its disadvantage is that it takes up the window space. Insert pic here.

Wall air conditioner is a unit that is built into the wall of a room. It has all the same properties as a window air conditioner. However, it requires additional wall opening to be created. The disadvantage of this unit is complicated installation. The advantage - it doesn't take up window space and can be installed at any height. These units have a better weather barrier than window air conditioners.  Insert pic here.

Portable air conditioners are self-contained units. Usually, they have casters to simplify their moving from one room to another. These units have a long and flexible hose that needs to be attached to a window to exhaust hot air.  Portable air conditioners are usually higher priced than wall and window units. Their two main advantages are: easy installation and portability.   Insert pic here.

Split-system unit is a less popular type of room air conditioner. It consists of two parts. One is hung on the wall inside the room and one is installed on the outside. They can be used to cool more than one room or large premises. Their disadvantage is the cost. These units are priced higher than other types. They provide more security than window types since the windows don't need to be open.  Insert pic here.

BTU is important to understanding the size of the air conditioner the user needs. The cooling capacity of most units varies from 5000 – 12 500 British Thermal Units. The general rule is: 20 BTU per 1 square foot of living space.

    •  Small window or wall unit's capacity ranges from 5000 to 6500 BTU. This capacity is good for up to 300 square feet. Usually these are the cheapest air conditioners

    •  Medium window or wall unit's capacity ranges from 7000 to 8 200 BTU. It will cool about 250 -400 square feet.  Such units are heavier, harder to install and will cost about twice as much as the small ones

    •  Large window or wall unit's capacity ranges from 9500 to 12500 BTU. It will cool a space of about 350 – 650 square feet. These models are heavy and costly but can efficiently cool a very large room.

Other factors besides BTU need to be considered when choosing the size of the air conditioner unit such as:

    •  Ceiling height (for high ceilings the capacity should be increased by 5 – 10%)

    •  Window and doorway size (large windows and doors need larger capacity)

    •  Heavily shaded room (capacity should be reduced by 10%)

    •  Very sunny room (capacity should be increased by 10%)

    •  Number of room occupants (500 BTU should be added for each person if the number of          room occupants exceeds 2)

    •  Location.  If the unit is located in the kitchen then the capacity needs to be increased by 3000 – 4000 BTU.

It is important to choose which room you want to place the air conditioning unit in. You need to consider such factors as the sunny or shady side, the amount of heat (kitchen or laundry room) and the size of the room

Efficient airflow. For built-in, portable and split-system units it is important to find a place with the best airflow. This question will best be answered by a professional technician. The right placement for perfect air flow might go against your décor plans.

Noise. Most of the room air conditioners are somewhat noisy. This factor must be considered when placing the unit near a bed. Also the external unit for the split-system might be very noisy and needs to be installed in a way to avoid bothering the neighbors.

Direct airflow.  If the unit is installed, the airflow is directed straight at a place where room occupants are usually sitting/sleeping; it can lead to health problems. Accordingly, it would be best to install the air conditioner high enough to avoid direct air flow.  This works with split-systems and wall units. Portable units can be placed in the opposite corner (if there is enough piping). Window units are fixed in one place so the airflow can't be adjusted.

Inverter technology. Usually, air conditioners are either working at 100 % capacity or not working at all. Inverter units regulate the speed of the compressor and maintain the preset temperature. Usually, such option makes air conditioners more efficient and less costly.

Reverse-cycle. Some air conditioner units have a heating option and can be used to heat up air in the winter. They don't cost much more than cooling-only air conditioners. These units are considered one of the cheapest ways to heat large spaces.

Mosquito traps. These are special protective screens on the window units that don't allow mosquitoes to get inside the room.  Insert pic here

Adjustable louvers. They can be adjusted vertically or horizontally to make the air flow in different directions.

Remote control will allow distant operation of air conditioners which is compulsory for models that are hung high. Insert pic here

Presence sensor. This feature allows the air conditioner to sense if there is a person in the room in order to continue working. The unit will shut down if there is no one in the room. Some models are equipped with a sensor that directs air flow to the area where a person is. This minimizes operation costs.

Sleep mode. The air conditioner can be set to a sleep mode for the time when people are sleeping so it doesn't work as extensively as when the room occupants are awake. This option will also regulate the air conditioner to produce less noise.

Different fan speed. More expensive models will have variable fan speed. The more speed settings there are, the better you can regulate the airflow. This is another money-saving option.

Programmable unit. You can program such a unit to keep different temperature at different times of the day.  Insert pic here

Timer. This option will allow you to set the time when you want your air conditioner to start working and the time you want it to stop. This is a cheap alternative to the programmable unit feature.

Intelligent cooling. Some air conditioners can be connected to your smartphone and operated remotely. This is a good option for the time when you want to come home to a cool room.

Slide-out chassis allow the unit to slide out for cleaning and maintenance. 

Filter type is important to the proper air conditioner operation.

    •  Standard – most popular common type. Needs to be replaced every once in a while

    •  Washable – these filters cost more but they can be washed and reused. They are durable and will last for a long time.

Extra features. Extra features are needed to make the room air conditioner operation more comfortable but they are not necessary for its proper work. Accordingly, if you are on a tight budget, such options as different fan speed, sleep mode and programmable units can be overlooked.

Cheapest models. The cheapest air conditioner model is the window type. These are the most popular models, accordingly, they are more widespread. It is easier to find a good promotion on such unit.

Energy-efficiency. Sometimes it makes sense to purchase a more expensive unit in order to save money in the future. Some options allow the air conditioner to consume less energy which in turn reduces the electricity bill.

Installation. Most of the room air conditioners can be installed without professional assistance. This allows a user to save a significant amount of money on installation. This is true for the most window, wall and portable units. Split-systems need to be installed by a technician.