Air Conditioner Guide: Everything You Need to Know About Air Conditioners

In the dog days of summer, most people choose to remain indoors rather than brave hot sidewalks and sunburns. But when the first serious heat wave arrives and shelter can't even be found indoors, stores sell out of relief in hours, sending hundreds of air conditioners on their way. As a result, people will often purchase whatever is available, with little regard for its specifications to the buyer's needs-- even that yellow-tinged sputtering job in the back of the local hardware store. Many people don't head to the store with home measurements and electric bills in hand and, as a result, end up with something that just doesn't quite fit. But with a little preparation it is possible to purchase a unit that meets the needs of both the consumer and the space, whether it's an entire duplex or one small bedroom.

Air Conditioner Basics

Air conditioners have both cooling and heating mechanisms. The cooling half blows cool air into the room, while the heating mechanism involves venting hot air out of the room. All types of air conditioners function according to this basic principle and are made up of the same basic components. The compressor compresses the coolant and raises pressure and temperature. The hot coolant runs through hot condenser coils in order to dissipate heat and condense into a liquid. An expansion valve causes the coolant to expand and evaporate into a cool gas, and then the low temperature coolant runs through cold evaporator coils, cooling the surrounding air. Fans are also a main component of air conditioners as they constantly circulate inside air over the cool coils and blow outside air over the hot coils, dissipating heat more effectively.

An air conditioner's power capacity is generally rated in BTUs, or British Thermal Units, with most room air conditioners falling between 5,000 and 30,000 BTUs. The practical effectiveness of a unit may vary depending on outside factors including how many people are in the space being cooled, what other electronics are functioning within the space and outside temperature. In general, a 5,000 BTU air conditioner will effectively cool a room of 100-150 square feet, 6,000 BTUs will cool a space of 150-250 square feet, 7,000 BTUs will cool a space of 250 to 300 square feet, and so forth. To estimate the necessary BTUs, find the square footage of the given space and multiply it by 35.

The recommended BTU rating, however, is not always applicable. For example, if the air conditioner will be in a room shaded from the outside, reduce the BTUs by 10%. If the space is exposed to ample sunlight, increase the BTUs by 10%. For a room that is regularly used by more than two people, add about 600 BTUs per person. For cooling a kitchen, add 4,000 BTUs (in consideration of heat generated by appliances such as the oven, stove and microwave.)

To find the EER, or energy efficiency rating of an air conditioner, divide the BTU rating by the wattage used. A higher EER means better energy efficiency, but also impacts the unit's price. Look for the Energy Star label to confirm a purchase with the most energy efficiency.

With the knowledge of different components and the importance of BTUs and EERs in the selection of the proper unit, the buyer must now decide which type of air conditioner will best suit his or her needs. The main difference between types of air conditioners is simply how the components are arranged, but knowing these differences can be especially important in deciding which unit is the correct choice.

The Different Types of Air Conditioners

The most common type of air conditioner is the generic window unit. Because these are designed to fit into standard windows that slide up and down, and window size is a large variable, size is an especially important factor in considering this type of unit. Measuring the height and width of the space reserved for the unit will ensure that the buyer doesn't purchase a unit that cannot be used.

Installation generally involves little more than opening the window, propping the air conditioner into the space and closing the window to hold the unit in place. In some cases, the edges of the air conditioner must be secured using screws in the window frame. Additionally, heavier units will require the preparation of added support. More powerful air conditioners are also larger and heavier and the installation of such may require more than one pair of hands.

Window units, also referred to as room air conditioners, generally have a cooling capacity of between 5,000 BTUs and 30,000 BTUs, with the most common being between 5,000 and 10,000 BTUs. Prices begin at around $100 for units with lower BTUs, and may reach $1,000 for significantly higher BTU ratings. Generally, one can expect to pay between $250 and $400 for a unit with a 10,000 BTU rating. (Look for sales at both the beginning and ending of the summer season.)

Casement Unit Air Conditioners

Although casement unit air conditioners are sometimes more difficult to find, windows that slide side to side necessitate this type of air conditioner. BTU ratings and installation are similar to regular room air conditioners, but because of a more limited selection, the price range is higher. In general, a casement air conditioner will cost $300 to $500.

Through-Wall Unit Air Conditioners

Through-wall air conditioners require a more complicated installation. This type of unit is installed into an outside wall of the house. The hole in the outside wall is lined with a metal sheath, which provides support for the unit. The installation of a through-wall air conditioner without this metal sheath can lead gaps through which cooled air can escape to the outside. Many through-wall air conditioners will act as window air conditioners if the homeowner does not want to install it through the wall, but the general advantage of this type of unit is that it does not occupy window space. (To insulate this unit during the winter months, measure the opening and purchase the appropriately sized insulated air conditioner cover.) Like window units, through-wall air conditioners are available with BTU ratings between 5,000 and 30,000, with prices ranging from $100 to $1,500.

Central Air Conditioners

Central air conditioners cannot be used in all homes and are only an appropriate choice if there is sufficient ductwork to allow the air to flow throughout the house. If the house's heating system involves electric heat or hot water baseboards and radiators rather than ducts, central air cannot be installed without an even larger price tag. If the ducts are available, installation tends to require a professional, causing largely varied prices.

Ductless Split Unit Air Conditioners

The ductless split system air conditioner places the air compressor outside of the house, connected through a small hole through the wall to the interior cooling unit. The location of the air compressor will reduce noise significantly. Ductless split units, which have an approximate BTU range from 10,000 to 30,000, are pricier than window units and typically require professional installation.

A comparatively new development, portable unit air conditionerss are ideal for rooms without windows, or with windows that cannot support the weight or size of an air conditioner. As the name indicates, these units are easily moved from room to room, especially convenient for those who would like to forgo multiple installations. These units use an exhaust system to vent the heat produced by the air compressor. The exhaust is then vented through attached tubes that can be set up to move air through a nearby window. Most portable units have between 7,000 and 30,000 BTUs of cooling power, although some units are much more powerful (and more expensive). Prices range from about $300 to over $10,000.

Portable air conditioners are not to be confused with portable air coolers, which use an entirely different method of cooling. In general, coolers do not have BTU ratings, because the technology has varying efficiency depending on conditions.

Rather than using an air compressor and condenser like an air conditioner, a cooler's mechanism involves a water tank and evaporation, useful in areas of low relative humidity, especially because the cooler itself acts as a humidifier. (Conditioners have a dehumidifying effect.) A cooler also uses less electricity and creates less noise than a conditioner. Approximate prices range from $80 to $150.

Air Conditioner Size, Strength, and Features

Armed with knowledge of type, technology, price and rating, it is time to head to the store. Final considerations should include overall air conditioner size, strength, and extra features.

Air Conditioner Size

Understanding what measurements to take depends on the type of conditioner required. For through-wall and split air conditioners, be sure to know the exact location of installation and take measurements of that area before making the purchase.

For window air conditioners, consider the inside dimensions of the window before purchasing. Considering the weight of the unit and the window's ability to support that weight is vital to selecting the correct window unit. (This is also important for installation-- the homeowner should be able to lift and remove the unit with minimal strain.) Optimal storage is another important size consideration.

Air Conditioner Strength

If the BTU rating is too low for the given space, the unit will run continuously without effectively cooling the room. This causes extra noise, energy consumption, and overall consumer irritation. An air conditioner with a BTU rating that is too high for the given space will also waste energy. While the space will cool rapidly, the conditioner will also cycle on and of continuously and rapidly, weakening the conditioner's ability to effectively dehumidify, as air circulation is limited. Use the rules described above to choose the perfect BTU rating for the given space.

Air Conditioner Features

Warranty

It is a good idea to supplement any large purchase with a warranty that will cover repairs or replacements for defective units. Some stores offer an extended warranty for an additional price.

Temperature Range and Settings

Digital displays allow for greater control over cooling, and can prevent the nighttime chill that the generic low/high dial models can produce. Consider the temperature increments; the smaller the increments and larger the range, the easier it will be to precisely cool the given space.

Fans

Fan settings affects air circulation and noise. It is important to choose a unit with enough fan settings (in smaller increments) so that it may adapt to changing conditions, such as the outside temperature and time of day (for noise.)

Energy Savers

Many units offer sleep or energy saver settings. These are useful for saving energy (and money!) without turning the unit on and off constantly. The room remains at a temperature that is manageable, allowing it to cool to a comfortable level more quickly when it returns to normal power.

Filters

Air conditioners contain filters that remove dust and other particles from air that is being sent back into the room. Filters should be cleaned or replaced often, so units with a slide-out filter are ideal. Another option is a washable filter, which can save the buyer money.

Additional Functions

Some models include additional conditioner functions like purifiers, or a "dehumidify only" option. A more expensive model might even include heating options. Consider all other characteristics of the room or rooms to be cooled before deciding if these extra features are appropriate or necessary.

Bottom Line

Air conditioners are not one-size-fits-all. Ensure that you aren't the only one without during the next heat wave by doing your research and shopping ahead of time. An air conditioner of the correct size will provide years of quality and comfortable cooling to your home.