Easy guidelines to determine your cooling needs

Whether you're getting a professionally-installed central air unit or a simple, window-based air conditioner, there's lots to consider before deciding on a model. We'll talk about how to choose the perfect unit to keep your home cool and comfortable.

Besides the size of the area to be cooled, you also need to consider the amount of insulation in the house, the level of shade your home receives, and the orientation, number, and size of your windows. Rooms on higher floors usually need more cooling than first-floor rooms.

Take your time when calculating your cooling requirements. If you choose a unit that's too small, it will be overtaxed and may not adequately cool your home. A unit that is too large may cool too quickly and not run long enough to properly remove humidity.

The cooling capacity of an air conditioner is measured in British thermal units (BTUs). You can have your dealer calculate your needs, or take out a tape measure and calculator and make the following calculations yourself:

1. Multiply the room's length by its width by its height to find the total volume of space that needs to be cooled.
2. Allow for the heat of the sun by multiplying the total volume by 16 for a north-facing room, 17 for an east-facing room, 18 for a south-facing room or 20 if the room faces west.
3. Factor for insulation by dividing the result by four if your house has poor insulation, five if the insulation is good or six if the house is super insulated.The resulting number will tell you how many BTUs of air conditioning that room needs.

Window air conditioners up to about 12,000 BTUs can usually run on a 120-volt electrical connection. That means that you can plug a unit into a standard household outlet. However, do not plug an air conditioner into a circuit that already supplies power to other household appliances. Be careful not to use an outlet that is controlled by a wall switch. An air conditioner larger than 12,000 BTUs may require a 240-volt line, which should be installed by a licensed electrician.

Like most electrical appliances, air conditioners have become much more energy efficient in recent years, but some models can still use significantly more electricity than others.

• Window air conditioners are given an Energy Efficiency Rating (EER). The higher the EER, the lower the energy consumption.
• Central air conditioners are rated with a Seasonal Energy Efficiency Rating (SEER). The higher the SEER, the better the energy efficiency.

Follow these guidelines and soon you'll be able to experience one of the best feelings around: coming in from the scorching heat into a cool, refreshing home.