Completed furnace maintenance on both systems. I checked all components and amps. I tested airflow and temp splits. I inspected the heat, exchanger and cleanliness of coils and blowers. Main floor furnace runs quite a bit more than the upstairs furnace so with the extra usage and moisture that has gotten on the system, the main floor furnace is in a rougher shape than the upstairs furnace. Upstairs furnace looks great, except for the dirty blower and blower wheel. When testing for carbon monoxide, I found none and I found no cracks or holes in the exchangers. The furnace exhaust connects from both furnaces and is rusted at multiple points to where if I were to push on the rust firmly I could push right through it. Spoke with homeowner about the exhaust and what could happen if they develop holes or fall apart. Homeowner has a home warranty that needs to approve repairs first.