A fan wheel (1, 1') comprising: a first and second end plate arranged at a mutual distance from each other, the first end plate having an opening which allows inflow to the fan wheel, and blades (5, 5') arranged between the first and the second end plate and joined to the first and the second end plate, whereby outer edges (8, 8') of the blades (5, 5') together with the first and second end plate delimit openings allowing outflow from the fan wheel, and wherein outer surfaces of the blades (5, 5') are inclined in relation to a rotation axis of the fan wheel (1, 1') such that the distance between the outer surfaces and the rotation axis is bigger at the first end plate than at the second end plate, characterized in that the first and second end plates have outer portions (11, 12) which protrude radially outward beyond the outer edges (8, 8') of the blades such that an outwardly open diffusion space is delimited by the outer portions (11, 12) of the first and second end plates and the blades (5, 5'), the outer portion of the first end plate protrudes radially outward beyond the outer edges (8, 8') of the blades (5, 5') with a distance (d) that is at least 5 to 10% of a diameter of the first end plate, the outer portion of the first end plate is generally curved or inclined towards the second end plate and the outer portion of the second end plate is generally curved or inclined away from the first end plate, and the width of the diffusion space increases outwardly, the blades (5, 5') are profiled to have a profile where the thickness of the blades varies between the outer edges (8, 8') of the blades (5, 5') and the inner edges of the blades while the thickness of the blades remains constant in a width direction of the blades. a first and second end plate arranged at a mutual distance from each other, the first end plate having an opening which allows inflow to the fan wheel, and blades (5, 5') arranged between the first and the second end plate and joined to the first and the second end plate, whereby outer edges (8, 8') of the blades (5, 5') together with the first and second end plate delimit openings allowing outflow from the fan wheel, and wherein outer surfaces of the blades (5, 5') are inclined in relation to a rotation axis of the fan wheel (1, 1') such that the distance between the outer surfaces and the rotation axis is bigger at the first end plate than at the second end plate, characterized in that the first and second end plates have outer portions (11, 12) which protrude radially outward beyond the outer edges (8, 8') of the blades such that an outwardly open diffusion space is delimited by the outer portions (11, 12) of the first and second end plates and the blades (5, 5'), the outer portion of the first end plate protrudes radially outward beyond the outer edges (8, 8') of the blades (5, 5') with a distance (d) that is at least 5 to 10% of a diameter of the first end plate, the outer portion of the first end plate is generally curved or inclined towards the second end plate and the outer portion of the second end plate is generally curved or inclined away from the first end plate, and the width of the diffusion space increases outwardly, the blades (5, 5') are profiled to have a profile where the thickness of the blades varies between the outer edges (8, 8') of the blades (5, 5') and the inner edges of the blades while the thickness of the blades remains constant in a width direction of the blades.