The paper presents experimental designs that can be used in modeling of the air-tightness of buildings as second-order functions using response surface method and corresponding experiment designs. The factors supposed to be significant for a model of building air-tightness—and thus those used in experiment designs—are the heat transfer coefficient for external walls, the heat transfer coefficient of the windows, and the position of the housing units with respect to the building envelope. We compared three-level full factorial and fractional factorial designs, as well as central composite designs and the Box–Behnken design.