At 2137 hours, Company 37 & 11 were dispatched to 6 South Riverside Drive in Ontelaunee Twp for a Carbon Monoxide Alarm activation. Crews from11 arrived on scene and the initial crews inside had immediate readings of over 50 ppm. Crews found CO in multiple units in this apartment complex. Chief 37 arrived and assumed command. It was found that these apartments were each using their wood stoves. After continued readings of CO, it was determined for Ladder 12 to be dispatched and check the chimneys. Ladder 12 arrived and went to the roof. Crews dropped chains into these chimneys and cleaned them all out. After ventilating again, it was determined that the zero CO readings were now holding. Crews took up their equipment and went available. We were clear at 2344 hours.