A supply air terminal unit (10) has a body (11) with side walls, top and bottom walls and an opening cover, which is opened to allow access for service work inside the structure. A wall structure (12) formed by needle-fin tubes (100) is fitted around a central fine filter (13), whereby the needle-fin tubes (100) are placed on top of each other in order to form a filter wall (12). A needle-fin tube (120) has needle-like fins whereby in its tube a heat carrier is made to flow in order to transfer heat into the air made to flow through the structure or in the opposite direction. The fine filter (13) covers an air outlet port (A2) located in the bottom (11a5) of the supply air terminal unit.