This report presents a methodology for assisting the planning of introducing storage into a DH&C plant. The methodology is divided into the solving of two sub problems; the existence problem, in this report referred to as the step one problem and the dimensioning problem referred to as the step two problem. The report contains a study on the technical design of a store and how the shape of the store affects the efficiency and a survey on short term operational optimisation of DH&C plants as well as a discussion on the storage optimisation problem and how optimisation uncertainties affects the dimensioning. The methodology for solving the existence problem, i.e. to find out whether a store should be further investigated or not, is presented. The methodology is based on historical data and the main idea behind this decision model is to study periods where the heat load is fluctuating around the maximum capacity of the base heat production. The necessity and appropriate size of a storage is evaluated by calculating the demand of energy above and below the actual production limit. Solving the dimensioning problem is to find the optimum size of heat storage for a given district heating plant. A methodology for solving this problem is presented. Non-linear operational optimisation models from the literature survey are used to determine the optimal operation of the system (dispatch problem) and dynamic programming is employed for finding the optimal size of the storage (unit commitment).