For the waste heat recovery from the flue gas of a 5.6 MW gas-fired boiler at a boiler house in Beijing, two deep-flue-gas?heat?recovery schemes—direct heat exchange and an electric?compression heat pump—were designed, leveraging the low?temperature return water conditions of the secondary network. Measured operating parameters were analyzed, a hybrid operation mode based on peak?and?valley electricity pricing was proposed, and a techno?economic evaluation of the three modes was conducted. The results indicate that the direct recovery mode features a simple system and high energy efficiency; however, it yields relatively high flue?gas temperatures. In contrast, heat?pump recovery requires three or more compressors to achieve greater heat transfer and lower flue?gas temperatures. Under the direct recovery mode, the first heat exchanger handles most of the temperature drop, and a single unit can meet the demand during low?load operation. The direct recovery mode boasts the shortest payback period of just 1.47 years, making it the most economically advantageous. The hybrid operation mode balances initial investment with operational benefits, reducing the payback period of the heat?pump?equipped system from 11.82 years to 4.59 years. This system can annually reduce carbon emissions by 29.18–65.01 tCO?.