A heat exchanger, a heat exchanger unit, and a refrigeration cycle apparatus are provided where deterioration in drainage and ventilation properties is prevented, an air passage is not easily clogged when frost forms, and both defrosting properties and heat exchange performance are achieved. A flat tube and a plurality of fins that are each a plate having a plate surface extending in a longitudinal direction and in a width direction orthogonal to the longitudinal direction are provided. The plate surface intersects a pipe axis of the flat tube. The plurality of fins each have an insertion portion in which the flat tube is inserted, a first spacer formed at a rim of the insertion portion and maintaining the interval, and a second spacer formed at a portion of the plate other than the rim of the insertion portion and maintaining the interval.