Air Conditioner Buying Guide

Efficient cooling

Air conditioners have a reputation for being environmental time bombs, in part for their energy consumption and in part for the coolants they use. Coolants are a necessity. An air conditioner works by pressurizing a refrigerant gas that absorbs room heat as it cools. The hot air is exhausted outdoors and the cold air gets blown into the room.

If you have an older air conditioner, it’s a good idea to replace it with a newer model. Stronger environmental regulations have led to better designs that prevent refrigerant gas from leaking and harming the environment.

Air conditioners have become better at managing energy consumption as well. Hard-to-read analog dials that you cranked all the way to the right for maximum cooling have been replaced by digital controls that let you set a precise temperature. Better air conditioners let you raise and lower the temperature during the day with automated timers and sleep settings. This last function lets you save energy while you sleep by automatically reducing cooling by a few degrees.

Btus and room size

Energy-efficient features won’t do much if the air conditioner you choose is too large or too small for the room you use it in. An air conditioner that is too small will always be on trying to reach the right temperature, while one that’s too large will cycle on and off frequently, which draws more power than longer operation. The cooling power of air conditioners is measured in British Thermal Units (Btus) per hour. One Btu is equal to the cooling needed to lower the temperature of one pound of water by one degree. Matching the Btu/hr rating for an air conditioner to your room size will give you the most effective cooling. Grab a measuring tape and calculate the square footage of the room you wish to cool by measuring its width and length and multiplying these two numbers. Use the chart below to determine your needs.

Room Size (square feet)	Btus/hr
100-300	5,000-6,000
300-600	8,000-9,000
600-1,000	10,000-15,00

These guidelines are a general rule of thumb, and it’s important to note that air conditioners are rated for standard ceiling heights of eight feet. If you have higher ceilings, or if you’re trying to cool a warmer, south-facing room, look for an air conditioner with more power. Poor insulation or drafts will also affect air conditioner performance, so it’s a good idea to remedy these problems if you have the right size air conditioner and it’s working too hard.

Window and wall mounts

Room air conditioners can either be mounted in a double-hung window or installed through an exterior wall in your home. Both methods are effective, but a well-insulated wall mount tends to perform a little better than a window air conditioner that uses stops to seal the gaps between the air conditioner and the sides of the window opening.

In general, wall-mounted air conditioners are a good choice for a room that needs to be cooled for more than half the year. Window air conditioners are best in places with cold winters, because you can remove them and let storm windows keep the cold out. Most air conditioners include side stops, which gives you the choice of using the air conditioner in a window or installing it through the wall.

Mounting an air conditioner through a wall requires the help of a builder. This is a structural change to your home that needs to be properly framed to ensure safety and prevent leaks. You may also have a choice between an air conditioner that plugs into a wall outlet and one that can be hard-wired into your home electrical system. If you live in a place where it snows, consider purchasing a fitted cover that will keep snow and ice out of the air conditioner’s compartment.

You can install a window air conditioner yourself. Measure the size of your windows and try to find an air conditioner that fits snugly, as you’ll get an efficiency boost by reducing the amount of space filled by the air conditioner’s side stops. Look for side stops made from flexible materials that won’t crack or break over time, and try to find side stops that offer some insulating value.

Be sure that your window sills are free of decay and strong enough to support the weight of an air conditioner. You’ll also need a three-prong electrical outlet near the window. Air conditioner cords tend to be on the short side, so keep this in mind when deciding which window to use.

Greener cooling

The U.S. Department of Energy reports that replacing a 10-year-old air conditioner with a modern, more efficient model will save an average of $25 a year on your electric bill. That means less electricity consumption and a smaller carbon footprint for your home.

Look for an air conditioner that has earned the Energy Star. These air conditioners are 10% more efficient than comparable models. Also look for an air conditioner’s Energy Efficiency (EE) rating. This rating divides the Btus/hr by the wattage an air conditioner consumes. Higher EE ratings provide more cooling with less power.

Need to know more?

• Energy Star Qualified Room Air Conditioners
  http://www.energystar.gov/index.cfm?fuseaction=roomac.display_products_html
• Boost Energy Efficiency With a New Air Conditioner
  http://www.energy.iastate.edu/news/pr/pr-newac.html
• Saving Energy: Heating & Air Conditioning
  http://www.powerhousetv.com/stellent2/groups/public/documents/pub/phtv_se_he_bu_000589.hcsp