The ornamental design for a fanheater, as shown and described.
1.-2. Fan heater
1.1 : Front
1.2 : Back
1.3 : Left
1.4 : Right
1.5 : Top
1.6 : Bottom
1.7 : Perspective
1.8 : Front view of component 1
1.9 : Left view of component 1
1.10 : Right view of component 1
1.11 : Top view of component 1
1.12 : Front view of component 2
1.13 : Left view of component 2
1.14 : Top view of component 2
2.1 : Front
2.2 : Back
2.3 : Left
2.4 : Right
2.5 : Top
2.6 : Bottom
2.7 : Perspective
Back and bottom views of component 1 are omitted as they are the same as back and bottom views of the combination (i.e. reproductions 1.2 and 1.6) respectively; back, right and bottom views of component 2 are omitted as they are the same as front, left and top views of component 2 (i.e. reproductions 1.12-1.14) respectively.