An analysis of the basic energy equation which describes the infrared system (IRS) operation is suggested as the basis for the adaptation methodology. First, it is necessary to do a sufficiently complete formula for the IRS figure of merit being adapted as the function of the IRS parameters. Secondly, it is useful to determine both a degree of various parameters influence on the adapted figure of merit and a possible range of its variation. Then it will be possible to evaluate the accuracy of the chosen adaptation method. As a simple example, the parametric adaptation of IRS sensitivity has been considered.