The Cost of Keeping Cool

As temperatures rise, so does interest in buying air conditioners. If you’re shopping for a window unit, there’s good news: Prices have decreased in recent years.

Still, the difference in models can be substantial. While a small unit can cost about $100, expect to pay many times that for a tricked-out jumbo unit. But bigger isn’t necessarily better.

Units are measured in BTUs—British Thermal Units. Generally, a model with 5,000-6,000 BTUs per hour cools rooms up to 250 square feet, and typically sells for between $100 and $350; 7,000- to 9,000-BTU models for rooms up to 400 square feet typically retail for $160 to $650; and units with 9,000 or more BTUs are best for larger rooms and may start at $250 but can cost $1,000 or more.

Some shopping tips:

• Based on room size alone, an air conditioner generally needs at least 20 BTUs for each square foot of living space.  So, if your room is 225 square feet (say 15 by 15) you would want an AC of about 4,500 BTUs (225 x 20 = 4,500).

• If the unit is for well-shaded rooms, reduce the necessary BTU capacity by 10 percent; add 10 percent if the room is very sunny.

• Add 600 BTUs for each additional person who regularly will be in the room.

• If the unit is for the kitchen, increase the capacity by 4,000 BTUs.

• For detailed specs that consider your location, window size and direction, house construction and other factors, Consumer Reports offers an online calculator.

• Expect to pay about $50 more for an energy-efficient unit, which use about 10 percent less power. These models typically have an Energy Star emblem. Also look for its EER (Energy Efficiency Rating): The higher that number, the more efficient it is.

• Once you buy, clean the filter every month—more if your home has pets or is very dusty. When possible, periodically hose the back of the unit (from outdoors) if debris has clogged cooling coils.