At approx. 13:25 an administrative line rang at the DVFD, Lt. C. Hudson answered the phone to find a female advising she & (3) three others complaining of headaches & dizziness from possible CO in their home. Lt. Hudson collected information, advised all subjects to evacuate the home & relayed information to EOC while a crew was getting ready. EOC dispatched the call & E731 was on the street at dispatch under the command of Chief Engineer J. Layton w/ a crew of (4) four. While enroute EMS was requested to be added to the call by Chief Engineer Layton, due to not being on the initial dispatch. Engine 1 arrived to find all subjects still in the mobile home & the crew advised by an occupant that a 5 month old was inside, asleep & not wanting to wake up. The crew off Engine 1 quickly evacuated the residence & a crew on air began to assess air quality using (2) two four-gas meters. The highest reading was (7) seven found in the rear of the residence. The source was determined to a malfunctioning oil furnace, with a bad roof jack. Crews from the Rescue Company placed an electric PPV fan in service an cleared the residence of CO. Due to DVFD EMS being on a run, Millsboro EMS transported (4) patients to BMC. DVFD crews secured the furnace & turned the residence over to the owner. Crews operated for 45 min before returning to service.