I Have an Underground Heating Network

"Eat with confidence" and "50,000-word setting outline to tell the whole story" The world is frozen, with the surface -60°C. Humanity hides in underground hives and relies on nuclear reactors to survive. I, Chen Dongzhi, am a plumber at the lowest level in the Outer Ring District - no powers, no system, and no memory of rebirth. There was only an HVAC drawing left by my grandfather, and a pair of hands that had been touching the valves in the dark for ten years. While others were struggling for a mouthful of hot water, I built a 16°C warm house in an abandoned pipe, grew mushrooms, and stocked up on calorie coupons. When the mortality rate of the official dispatched team was 70%, I designed a "hot corridor" to evacuate the entire hospital with zero casualties and brought back tons of medicines. When the Governor used heating as a weapon of power, I used waste heat recovery to lay out an underground heating network covering the entire hive.