A fire started in the heating system underneath the floor at a residence at the pioneer trailer park at approximately 5:30 pm on Tuesday evening.  First arriving units from the Fire Department were on scene within one minute and found fire showing on the side of the building and all occupants were evacuated.  First and second due engines were on scene within three minutes.  The fire was under control within 10 minutes of the original dispatch.  No one was injured during the incident and the cause was undetermined.