A manufacturing plant produces water heaters under a make to order production strategy, and wishes to estimate its response time to deliver orders for its clients. In order to minimize the response time for a given order, the plant needs to schedule resources and operations accordingly. We present a decision support system to assist the plant manager in the estimation of the response time to deliver the heaters specified in a given order. The system uses heuristics for solving a resource-constrained project scheduling problem. A particular heuristic procedure performed better than the minimum slack heuristic in many cases.