A multi-chamber heat exchanger header includes a header housing and an insert. The header housing has a first wall and a second wall generally opposite the first wall where the first and second walls define a track. The insert is positioned to engage with the track such that the insert separates the header into first and second manifold chambers. A method for forming a multi-chamber heat exchanger header includes extruding a header housing having first and second manifold chambers and a track, positioning an insert in the header housing to engage with the track, and welding or brazing the insert to the header housing.