SIR refers to “Savings to Investment Ratio.” It is basically a calculation of whether a modification to a home will pay for itself in energy savings. SIR is a most often used by the U.S. Department of Energy Weatherization Assistance program to determine the cost effectiveness and energy savings of applying weatherization measures (e.g. adding additional insulation to the attic).
It is the ratio of the savings generated by the weatherization project to the cost of the project. SIR is …