The luxury of central air conditioning isn't always available when you move to a new location. A window or portable air conditioning unit may be your best choice to keep cool in hot temperatures. Unlike a basic ceiling, oscillating, or box fan, an air conditioner makes cool air instead of circulating room temperature air.

What to buy, how to buy, where to buy are all questions you have to ask yourself. Most people want to save money on whatever they purchase: be it food, gasoline or a cooling system. Cheap air conditioning units, both window types and portable, are readily available at your local hardware, department store or specialty store.

Unit Types and Calculating BTU

Knowing what you need to accomplish the goal of cooler air is the first step. Landlords and apartment complex managers do not often allow renters to install window air conditioning units due to potential damages and other restrictions. A portable unit would be the answer to your problem under those circumstances. Portable AC units are also very useful in storage buildings, garages and workshops that aren't connected to your home or have limited window space.

The size of the area to be cooled is of utmost importance when choosing the size of the AC unit. It's probably pretty obvious that a bigger unit would be required to cool a larger area effectively. 20 BTU per square foot is the average estimate for calculating the BTU needed to cool an area. The equation to calculate BTU is sqft x 20 = BTU Needed.

Example: You're cooling a room that measures 15ft by 20ft. Using the formula above, you'd calculate the square footage by multiplying the width by the length of the room. Our example room is 15ft x 20ft = 300sqft. Multiply the square footage by 20 BTU per square foot: 300sqft x 20 = 6,000 BTU is needed to cool our example room under optimal circumstances.

Please keep in mind that the size of the room is not the only factor. A room that receives a lot of sunlight requires more cooling than a room that is well-shaded. Along those same lines; more insulation, heat-producing appliances, size of household and humidity play roles in the effectiveness of an air conditioning unit. Energy efficient doors and windows help immensely with heating and cooling issues.

Portable Air Conditioning Units (http://www.dealhack.com/archives/2010/05/save_on_air_conditioners_ice_m.html)

Sunpentown SF 613 Evaporative Air Cooler with Remote Ionizer is a portable unit with a starting price of around $90. This system will cool your room up to 12 degrees only using the same amount of power as a basic light bulb. The air is distributed in a stream and has an SF-613 that controls the airflow by computer. Though it isn’t rated as an air conditioner, it is called an air cooler as it has an Ionizer built in which is designed to purify the air. This unit would be great for a small room or dorm.

Soleus Air PE2-09R is available at 9,000 BTU and is an Evaporative Portable Model. It has 2 Fan Speeds and comes with a programmable remote control with 24 hour on/off controls. It has a three color display with loss of power protection. This unit starts out around $200.

Frigidaire offers an 11,000 BTU Portable Air Conditioner. This is one of the best and most affordable portable air conditioning units according to many online reviews. It easily cools an area of about 1,000 square feet. The unit can be set as low as 62 degrees and is on wheels. The price tag begins around $300 to $400.

Window Units

Window air conditioning units can be as small as 11 inches x 15 inches. Frigidaire makes the FAX052P7A - 5,000 BTU Mini Room Air Conditioner. Starting price is roughly $103 at several online retailers. Included with this model is a remote thermostat, clean air filtration and low voltage start-up. This unit is Energy Star qualified.

Haier makes the HWR06XC9 Window Air Conditioner Cooler - 6000 BTUs. It has 115 volts of power with three fan speeds. Key features include all top discharge air flow, ultra quiet operation "quick snap" curtain install. This model can be purchased online for just under $140 for a new unit.

Larger rooms need more cooling and LG Electronics, Inc. makes the LG 15,000 BTU window mounted unit (http://www.dealhack.com/archives/2008/06/10_off_window_portable_ac_unit.html. This is an Energy Star remote controlled window air conditioner with electronic controls. It’s designed to cool approximately 800 square feet. It has 3 cooling settings and 3 fan speeds, as well as 4-way air direction.

Things to Keep in Mind

The square footage of the area to be cooled is the primary concern, followed closely by environmental and household factors. Any air conditioning units that are too small will produce unsatisfactory results, but a unit that is too big is wasted energy. Using the equation sqft x 20 = BTU needed will give you a great baseline idea of the size unit you will need.

Portable units are good for small, enclosed spaces while window units are better for larger rooms or whole houses. Some installation is required if you purchase a window unit, so basic understanding of measurements and how to use a screwdriver is needed.