More Housing Units Have Central Air-Conditioning

In 1978, only 23 percent of U.S. housing units had central air-conditioning (Figure 1). By 1997, the share had increased to 47 percent. During the same period, the share of housing units with window/wall units dropped from 33 percent to 25 percent, and the share of housing units with no air-conditioning equipment dropped from 44 percent to 28 percent.

As would be expected, the South, with its warm, humid climate, consistently had the highest percentage of housing units that had air-conditioning. By 1997, 93 percent of the housing units in the South had some type of air-conditioning. By contrast, only 41 percent of the housing units in the West had air-conditioning.

The Northeast differed from the other Census regions in that the share of housing units with window/wall units (41 percent in 1997) exceeded the share with central systems (22 percent in 1997). In all other regions in 1997, the share with central systems exceeded the share with window/wall units. The reason that the Northeast has a higher percent of housing units with window/wall units is probably a combination of climate, price of electricity, and the share of housing units that are in older apartment buildings.

In all four Census regions, the share of homes with central air-conditioning equipment increased from 1978 to 1997 and share without any air-conditioning equipment decreased (the decrease in the West Census Region, however, was not statistically significant).

Air-Conditioning Is Being Used More Often

The share of homes with central air-conditioning that report using it "all summer long" has increased from 33 percent in 1981 to 52 percent in 1997 (Figure 2). The share of homes with window/wall units that report using air-conditioning "all summer long" increased from 11 percent in 1981 to 21 percent in 1997.

Households with central air-conditioning equipment use their equipment more often than those that have only window/wall units. In 1997, 51 percent of the households with window/wall units reported using their equipment only a few times, 25 percent reported using it "quite a bit," and 21 percent reported that they used it "all summer long." By contrast, 26 percent of the households with central air-conditioning equipment reported using their equipment only a few times, 22 percent reported using it "quite a bit," and 52 percent reported that they used it "all summer long".

Not surprisingly, households in the South are big users of air-conditioning equipment. In 1997, in the South, 69 percent of the households with central air-conditioning equipment reported using it "all summer long" and 40 percent of the households with only window/wall air-conditioning equipment reported using it "all summer long" (Figure 3). The rest of the country uses air-conditioning equipment less frequently than the South.

Increasing Electricity Consumption for Air-Conditioning Is Moderated by Efficiency Gains

From 1978 to 1997, the total amount of electricity used in the residential sector increased from 2.47 quadrillion Btu in 1978 to 3.54 quadrillion Btu. Over the same period, electricity used for residential air-conditioning rose from 0.31 quadrillion Btu to 0.42 quadrillion Btu. Among the reasons air-conditioning electricity use did not rise more is the increasing efficiency of air-conditioning equipment.

A standard measure of air-conditioning equipment efficiency is the Seasonal Energy Efficiency Ratio (SEER). For a given piece of equipment, the higher the SEER, the greater its efficiency, and the lower its electricity consumption. The average SEER of central air-conditioning equipment sold in 1978 was 7.34 (Table 1)). In 1997, the average SEER was 10.66, indicating a significant improvement in the efficiency of air-conditioning equipment.

In addition to improvements in equipment efficiency, at least two other factors affect air-conditioning electricity consumption. One factor is the population shift to the South, where air-conditioning use is greater because of the warmer climate. A second factor is the improvement in housing construction, particularly as regards insulation. In general, a better insulated house has a lower the need for cooling and will consume less electricity for air-conditioning.

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