Was here for a furnace cleaning. Customer was also having trouble heating the second floor. Performed preferred customer furnace cleaning. Completed furnace cleaning form. The furnace is running normally at this time. Took a temperature split on the furnace. The furnace is running a little cool at 32 degrees. Brought it to the customers attention that the furnace may be a little undersized for the house. Adjusted some air flow dampers in the basement to try to heat the second floor better. Instructed the customer to turn the fan button on the thermostat to the on position to help circulate the air in the house.