Performed yearly maintenance and safety checks on 20 Bryant furnace. Found 49 ohm ignition. 13%o2. 12 ppm co in supply. 40 degree deltat. Furnace properly cycled into high stage. Running with 7.9%o2 7ppm co in flu. 53 degree deltat. No concerns at this time. Left new 16254 filter under service plan. Customers current filter is clean. Customer wants to drop filter coverage for next renewal.