On 12-09-18 at 9:30am Engine 58-2 , Engine 61-1 and Tower 54 were alerted for a reported gas leak in the boro. Micu 58 was first arriving unit and updated that it was not a gas leak but a possible CO leak. Engine 58-2 arrived on location and started evacuating the building. Engine 61-1 was staged at the hydrant in case water supply was needed. Once it was confirmed CO leak with 127 PPM in the subdivision command brought Engine 61-1 to the front of the building and were ordered to set up ventilation in the entrance and then assist with interior operations. Crew from engine 58-2 located the suspected CO Leak and shut down all furnaces. Once the source of the leak was confirmed, Tower 54 members went to the roof to look for clogged ventilation pipes.. At this time it was narrowed down to one furnace. Command placed Tower 54 and Engine 61-1 back in service. Crew from engine 58-2 remained on location until the building service repair company arrived and took over. Crews Cleared the scene with no injuries reported.