San Bernardino furnace install work is dominated by replacement of aging mid-century equipment. Arrowhead, North Park, and central San Bernardino homes built 1950-1990 frequently still run 80% AFUE gas furnaces from the 1990s — well past 20-year service life with cracked heat exchangers becoming the failure mode that condemns the equipment. Replacement-with-upgrade to 95%+ AFUE high-efficiency typically wins the cost-benefit conversation: SoCalGas rebates ($200-$800), 15-20% annual gas savings, and the cracked-heat-exchanger CO risk eliminated. Newer North End and Verdemont neighborhoods (1990s-2010s) usually run 90-95% AFUE condensing furnaces already with cleaner failure modes — same-tonnage replacement at end-of-life with no retrofit work needed.