To find the most cost-effective RAC for your needs, follow these steps:
1. Select the right size. An undersized unit won't be able to cool a large room, while an oversized unit will cycle on and off frequently, which increases electricity consumption and decreases the unit's overall efficiency. An oversized unit may also cycle off too quickly to extract sufficient humidity from the air. You can calculate appropriate size yourself, have an HVAC contractor do the calculation for you, or use the rules-of-thumb chart that follows (Table 1).
Table 1: Capacity rules of thumb for room air conditioners
Rules of thumb for estimating air conditioner size vary by manufacturer. This example, from Carrier, includes the following suggestions for adjustments: If a room is heavily shaded, reduce capacity by 10 percent; if the room is very sunny, increase by 10 percent; and if using the unit in a kitchen, increase capacity by 4,000 Btu per hour.
2. Look for high energy efficiency. A unit's efficiency affects its operating cost. In the U.S. and Canada, energy labels that display the energy efficiency ratio (EER) must appear on room air conditioners. Other factors being equal, the higher the EER, the more energy efficient the unit—and the lower the operating cost (Figure 1). Energy labels also indicate expected energy cost and show how a product compares to the least and most efficient models available.
Figure 1: Operating cost for 10,000 Btu per hour room air conditioner
Other factors being equal, the higher the EER, the lower the operating cost. In addition, savings from higher-efficiency room air conditioners are much more substantial where operating hours are longer.
The Energy Star program, which is jointly operated by the U.S. Environmental Protection Agency and the Department of Energy, establishes an efficiency specification above the federal standards. RACs that meet these specifications are awarded the Energy Star label, which helps consumers and others to readily identify high-efficiency products. Visit the Energy Star web site for room air conditioners to check the product list for models you’re considering. This site can also help you calculate the right size for your application.
In addition, the Consortium for Energy Efficiency offers a program known as the Super-Efficient Home Appliances Initiative for Room Air Conditioners (PDF). The initiative’s goal is to encourage the use of high-efficiency RACs. As of April 2014, the minimum EER requirements for RACs that qualify for the initiative range from 9.8 to 11.8, depending on their size.
3. Determine which unit is most cost-effective. Although you'll want an efficient air conditioner, you may not need the most efficient one on the market, especially if you live in an arid climate with few months of cooling needs. Consider both the initial price and annual operating costs () as you compare models so you can determine the lifecycle cost. If the annual operating cost savings add up in a reasonable number of years to the additional cost of the more efficient unit, the more efficient unit will be the better buy.
Here are some other issues to keep in mind as you're shopping:
- Look for an "energy-saver" switch. The energy-saver switch causes the air conditioner's fan and compressor to cycle on and off together, reducing energy use.
- Verify that you'll get good moisture removal if you live in a humid climate. Manufacturers label the dehumidifying capacity of room air conditioners according to moisture removal in pints per hour. An HVAC contractor can calculate how much dehumidifying capacity you'll need. Be aware that increased efficiency can decrease dehumidification capacity.
- Listen. All room air conditioners make some noise, but levels vary widely. Listen to operating models if possible and check independent consumer guides for information on noise levels of the units you're considering. The ConsumerSearch web site rates RACs from 5,000 to 15,000 Btu and includes noise among its test categories.