Fan assembly comprising a fan wheel rotatably arranged around an axis in a fan duct; said fan wheel comprising: a first side, said first side comprising: an inner periphery and an outer periphery, a second side, said second side comprising: an inner periphery forming a fan wheel inlet and an outer periphery at least four curved wings; said at least four wings extending between said inner and outer periphery of the second side and said at least four wings extending between said first side and said second side, such that channels are formed between said wings and said first and second side, said channels comprising: an inlet (C i), arranged at said inner periphery of said second side and having a first cross sectional area, an outlet (C o), arranged at said outer periphery of said second side and having a second cross sectional area, the fan assembly being characterised in that the inner periphery of the second side is arranged at a first distance (H i) along the axis from the first side and the outer periphery of the second side is arranged at a second distance (H o) along the axis from the first side, said first distance (H i) is larger than the second distance (H o) such that the cross sectional area of the channels at the inlet and the cross sectional area of the channels at the outlet are substantially equal. a first side, said first side comprising: an inner periphery and an outer periphery, an inner periphery and an outer periphery, a second side, said second side comprising: an inner periphery forming a fan wheel inlet and an outer periphery an inner periphery forming a fan wheel inlet and an outer periphery at least four curved wings; said at least four wings extending between said inner and outer periphery of the second side and said at least four wings extending between said first side and said second side, such that channels are formed between said wings and said first and second side, said channels comprising: an inlet (C i), arranged at said inner periphery of said second side and having a first cross sectional area, an outlet (C o), arranged at said outer periphery of said second side and having a second cross sectional area, the fan assembly being characterised in that the inner periphery of the second side is arranged at a first distance (H i) along the axis from the first side and the outer periphery of the second side is arranged at a second distance (H o) along the axis from the first side, said first distance (H i) is larger than the second distance (H o) such that the cross sectional area of the channels at the inlet and the cross sectional area of the channels at the outlet are substantially equal. said at least four wings extending between said inner and outer periphery of the second side and said at least four wings extending between said first side and said second side, such that channels are formed between said wings and said first and second side, said channels comprising: an inlet (C i), arranged at said inner periphery of said second side and having a first cross sectional area, an outlet (C o), arranged at said outer periphery of said second side and having a second cross sectional area, the fan assembly being characterised in that the inner periphery of the second side is arranged at a first distance (H i) along the axis from the first side and the outer periphery of the second side is arranged at a second distance (H o) along the axis from the first side, said first distance (H i) is larger than the second distance (H o) such that the cross sectional area of the channels at the inlet and the cross sectional area of the channels at the outlet are substantially equal. an inlet (C i), arranged at said inner periphery of said second side and having a first cross sectional area, an outlet (C o), arranged at said outer periphery of said second side and having a second cross sectional area, the fan assembly being characterised in that the inner periphery of the second side is arranged at a first distance (H i) along the axis from the first side and the outer periphery of the second side is arranged at a second distance (H o) along the axis from the first side, said first distance (H i) is larger than the second distance (H o) such that the cross sectional area of the channels at the inlet and the cross sectional area of the channels at the outlet are substantially equal.