Oak Hills sits at 3,600-4,200 ft elevation, which makes furnace installation higher-stakes than in lower-elevation HD cities. Winter overnight lows here hit the high teens regularly, lower than Hesperia or Victorville. Furnace failures during cold snaps can drop indoor temps to dangerous levels within hours, so equipment reliability and right-sizing matter more here than down in valley cities. Larger Oak Hills custom homes (Caughlin Ranch, Caughlin Estates, Apple Valley Hills boundary) typically need 100-120k BTU furnaces vs the 60-80k BTU systems common in tract homes. Bigger furnaces have bigger heat exchangers, larger gas valves, and longer install timelines. Manual J load calculation done on every install - square-foot rules consistently oversize Oak Hills custom homes by 25-40%, which causes short-cycling and stress-fractures heat exchangers fast at this elevation. Mixed gas service (SoCalGas + propane) means we confirm fuel type at the door and carry both natural gas and propane parts on every Oak Hills dispatch.