The cost of operating central air versus window air conditioners is dependent upon the amount of space that needs to be cooled. In small spaces, cooling with well-placed window units is generally more cost efficient while central units are less expensive overall for large homes.
Although they are less efficient than central air conditioning units based primarily on their components, window air conditioning units are the most economical solutions for single rooms or small spaces because they use less electricity. Using several window units, however, lessens cost efficiency because the more of them that are running, the more electricity they use. In large spaces, therefore, central units are generally both the most energy efficient and cost-effective solution.