The rapid development of cities and the improvement of residents’ living standards cause excessive building energy consumption. As a northern coastal city in China, Dalian’s heating energy consumption in winter is considerable. For a residential area in Dalian, the hourly heat load throughout the year and the building energy consumption were simulated using Designer’s Simulation Toolkit. The capacity of the seawater source heat pump was optimized to minimize power consumption. Plan II performed best in terms of annual power consumption, saving 19.5 and 14.8% of electricity compared to Plan I and Plan III. Comparing the coal saving rate with the traditional boiler room and small chiller unit plan, the coal consumption was reduced by 30 tons, achieving the goal of energy saving and consumption reduction. The developed method in this study can be a reference for heating in coastal cities.