Every year when the summertime heat and humidity hit home large numbers of shoppers will descend on the big box stores or search the internet for some type of air cooling unit.

Everyone’s first choice is the window air conditioner. They’re easy to install and operate, relatively inexpensive, and do a reliable job of cooling and dehumidifying.

But many home owners and apartment dwellers, for a variety of reasons, are unable to install a window unit or are out-right prohibited from doing so by the landlord or home owner’s association.

With the window A/C out of the picture, three popular options remain: The fan, the portable swamp cooler, and the portable air conditioner.

Although the house fan is imminently portable and creates a good stiff breeze it does nothing to reduce humidity. And the portable swamp cooler actually adds moisture to the air, which is fine if you live in the desert, but not if you live in Alabama. So for most of us the only viable alternative method of cooling and dehumidifying is the portable air conditioner.

1. Contrary to what you might have heard or read there is no such thing as a vent-less portable air conditioner. Since a portable air conditioner uses a compressor for cooling, and compressors generate heat, the heat from the compressor must be vented to the outside through a hose and window vent.

2. The number of BTUs you should look for in a portable air conditioner depends on the size of the room and the heat load. Heat load in this case simply means how hot it gets where you live.

Realistically speaking, if your summers are very hot and humid, you would probably need around 50 BTU's per square foot for adequate cooling. In areas where summer is something you wish for in August 40 - 45 BTU's per sq. ft. is sufficient.

If the square footage of the room you want to cool falls in between air conditioner BTU sizes go with the next highest BTU size.

3. The EER, or Energy Efficiency Rating, is the ratio of BTUs per hour to the number of input watts. Models with an EER rating of 10 or better are the most energy efficient. If the EER rating isn't mentioned in the product description you can figure it out by dividing wattage into BTU's.

Example: 14,000 BTU/1,200 watts = 11.66 EER.

4. R-22 is a refrigerant that has been widely used in air conditioners for many years. It has been deemed hazardous to the environment and will be phased-out starting in 2010. The replacement for R-22 is the more eco-friendly R-410A. There are still units for sale manufactured before 2010 that use R-22, so if R-410 isn't specifically mentioned in the product description, you could assume the unit in question is still using the old R-22 refrigerant.

Another positive environment related change in the manufacture of portable air conditioners is compliance with the RoHS directive. The RoHS (Restriction of Hazardous Substances) directive restricts the use of lead, mercury, cadmium, and other heavy metals in the manufacture of electronic equipment.

5. Dual Hose vs Single Hose Units – Once again, despite what you might have heard or read, no definitive study has ever been conducted that proves (or disproves) that a dual hose model is more efficient than a single hose model.

Dual hose units are said to be more efficient because the intake air comes from the outside (hence the second hose), as opposed to a single hose unit which intakes air from within the room being cooled.

The argument against a single hose appliance is it will eventually start to exhaust the cooled air from within the room. But you can counter this by surmising that a portable air conditioner will run more efficiently when the intake air is already pre-cooled as opposed to 90° air being sucked in from the outside by a dual hose unit.

One way or the other, the most persuasive argument for purchasing a particular appliance is usually price, and single hose models are slightly less expensive than their double hose cousins.