Saying there are 100 million housing units in the United States hasn’t helped researchers distinguish between the hvac systems in a 3,000-sq-ft colonial house and those in a 750-sq-ft apartment.

Now, however, the study by Lawrence Berkeley National Laboratory divides the country’s housing sector broadly between 67 million single-family detached homes (including manufactured housing) and 33 million housing units in multifamily buildings.

As shown by the charts, only 17% of all 100 million housing units have no air conditioning. Breaking that housing total down, slightly more than one-third of the single-family sector has central cooling, 23% have one or more window units, 8% have heat pumps, and 3% have evaporative cooling (“swamp coolers”).

This means that the add-on market is at least 28% of the total — about 19 million homes.

Multifamily picture

The pattern is slightly different for the 33 million units in multifamily structures (condos, apartment buildings, and the like).

Relatively fewer of these (28%) have central cooling (from rooftop units or chillers), while 29% have one or more room units, followed by 6% heat pumps.

More than one-third (37%) have no cooling.

Source: Energy Data Sourcebook for the U.S. Residential Sector, available from the Office of Scientific and Technical Information, P.O. Box 62, Oak Ridge, Tenn. 37831; 615-576-8401.