Consumer Reports recently tested air-conditioners in a temperature- and humidity-controlled room.

The new federal tax credit might be making you think of adding central air or upgrading your system. According to Consumer Reports, the easiest way to save money on cooling this summer is to get the right cooling system for the space, whether using a central air system, a window unit or a ceiling fan.

In CR’s recent tests of 29 window A/Cs, all did an excellent job at cooling, but some were much noisier than others. CR identified six recommended models for $260 or less. The Friedrich CP06E10 ($260) and Sharp AF-S60PX ($190) were among the quietest models in the small category (5,000 to 6,000 Btu/hr.). The Friedrich and Frigidaire FAA055P7A ($180) did better in brownout tests.

In the midsized category (7,000 to 8,200 Btu/hr.) the Kenmore 76081 ($200) and the Frigidaire FAA087S7A ($200) scored excellent in brownout tests and operated quietly on low. For large window units (9,800 to 12,500 Btu/hr) CR named the Kenmore 75101 ($240) and the Kenmore 75121 ($300) CR Best Buys. They performed very well in brownout tests and were quiet on low settings.

Central air

When it comes to central air conditioners, reliability is crucial because breakdowns are inconvenient and costly. CR conducted a Product Reliability Survey of more than 32,000 readers who purchased central air systems (without heat pumps) between 2002 and 2008. Almost two-thirds of those who had a repair said their central air conditioning broke down for a day, and 31 percent reported a complete system failure. Forty-eight percent spent $150 or more to fix the problem.

Trane, the market leader, along with Rheem and Ruud were found to be reliable central-air brands and their systems were less likely to need repairs than those from Goodman and Heil, according to the survey. Based on reports from more than 17,000 readers with heat-pump-based cooling systems, those from American Standard, Bryant, Carrier, Lennox, Rheem, and Trane were equally reliable.

New central air conditioning systems are 20 percent to 40 percent more efficient than those made 10 years ago, and now, the federal government is offering a tax credit of 30 percent, up to $1,500, for replacing or adding central-air-conditioning systems or split ductless units.

Ceiling fans

Though they don’t remove humidity, ceiling fans can be an inexpensive alternative to window units, and they cost less to run. A 52-inch-diameter fan is ideal for rooms that are 225 to 400 square feet, while a 42- to 44-inch fan will cool a 144 to 225 square-foot room. The higher the cubic feet per minute, the more air movement. Ceiling fans with the most airflow were the noisiest in CR’s tests and fans with blades that have ridges or bumps were often noisier than those with smooth blades.

Doing it right

Getting the wrong size is the most common mistake people make, regardless of the type of cooling system. Purchasing a unit with too small a capacity could lead to inadequate cooling, while a unit that’s too large could lead to a cold, damp space. CR offers these tips:

• Upgrading central air. Don’t automatically buy the same-sized system. Changes that have improved energy efficiency, including new windows or added insulation, can reduce cooling needs, while added rooms could increase needs.

• Adding central air. Adding a central system is relatively straightforward if the home already has ductwork for heating. Contractors should use a duct-sizing method like the Air Conditioning Contractors of America’s Manual D to make sure there are enough supply registers to deliver sufficient air to the right spots. Leaky or uninsulated ducts can reduce system efficiency considerably.

• Window units. Energy Star-qualified window models use about 25 percent less electricity than those made before late 2000. Use the sizing calculator at www.ConsumerReports.org to determine the right size.