If it's blowing air out then it will have to be sucking air in.
The chances are that air will be getting in where it should not be entering. On a cylinder vacuum cleaner it's often a split hose -you will need to examine your machine to find the place. Tissue paper might help - where it sticks to the outside.
The air that comes out is used to cool the motor so it's a good thing that you feel the air to be warm.
Good luck..., June 2015