A method for designing a quench box having first and second blastheads for tempering at least first, second and third sheets of glass each having a different shape is disclosed. The method comprises (i) using the shape of at least the first and second sheets of glass to calculate a first average surface; (ii) using the first average surface to calculate a quench surface of first and second quench modules of the first blasthead; (iii) using the first average surface to calculate a quench surface of a first quench module of the second blasthead; and (iv) using the shape of at least the third sheet of glass to calculate a quench surface of a quench module that replaces a quench module of the first and second blastheads when used to temper the third sheet of glass.