On March 29, Ambulance 364 was dispatched to a hotel for a child having a seizure. While vitals were being taken, an alarm on our medical diagnostic equipment sounded, indicating higher than normal levels of carbon monoxide. This finding prompted Engine 351 to be dispatched to the location for air sampling and monitoring. Engine 351 found over 100 parts per million (ppm) between the counter and the pool area. At this point, Engine 351 personnel donned their self contained breathing apparatus and continued to the pool area were readings maxed out the diagnostic instrument at 499 ppm. Engine 351 established command and pulled the fire alarm to evacuate the 31 occupied rooms within the hotel. As guests evacuated the facility, additional symptomatic individuals were found. Additional assistance was requested by command for patient evaluation and transport. Overall, seven patients were transported to the hospital and several more were treated with Oxygen. An investigation found that the pool heater and/or ventilation system had failed and caused CO to accumulate in the hotel.