2 furnace pm check complete. Changed filters and added a citrus scent to them to bring extra freshness to the house! Upstairs system- Thermostat is a mercury thermostat and therefore no longer up to code, being older it's not as reliable. Recommend upgrading thermostat. Tested combustion and found safe carbon monoxide levels, slightly high oxygen levels (but not bad) with the furnace operating at 82% efficiency. Found a very rusty evaporater coil, likely to leak. Tested static pressure and found air to be properly balanced. Found flame safety running very weak, close to failure. Found ignition system worn with silica dust build up. Recommend repairs. Water safety is not up to code, recommend adding on. Dusted out furnace cabinet and cleared barometric tubing. Main level system- Tested combustion and found safe carbon monoxide levels, good oxygen levels, operating at 80.6% efficiency. Found weak flame safety, could fail at any time. Found worn ignition system with silica dust build up