Arrived on site for two furnace maintenance both furnace are supplied with natural gas. Upon arrival no one was at the house. Customer let me towards the furnace and the basement and the Attic by phone. Started up the unit in the basement with a thermostat, unit started up normally. Cut off the gas Supply from the furnace in the basement to operate it on safely. Hooked up temperature probes, static pressure probes, manometers and multimeter on the unit to ensure proper operation. Unit pressure on a manifold on high heat was peeking at 3.9, reduced it down to 3.4 for safety, nameplate says Max should be 3.5. Combustion analyzer was also inserted into the flu pipe to level carbon monoxide and rate the efficiency of the unit. Unit was running perfectly.