Borough units and Company 38 responded to the 400blk of W Louther St for a report of smoke in the house. While enroute HQ advised C141 of smoke filling the first floor and tenants were evacuating. Investigation reported smoke on all floors and found a fire in the furnace in the basement. Command 3 upgraded the box to the first alarm assignment. One line was used for extinguishment. Crews operated in the basement overhauling the HVAC piping and confirmed all active fire was held to the basement level. Command reduced the box to the original assignment to handle ventilation. Thank you to New Kingstown Fire Co. for transferring to Company 41 for the duration of the incident.