A closed channel rotary regenerative air preheater includes element supporting baskets that have first heat transfer elements having first arches arranged in an alternating order with second heat transfer elements having second arches. Each of the first arches has a first apex and a concave segment extending therefrom and each of the second arches has a second apex and a convex segment extending therefrom. Each of the convex segments is nested in a respective one of the concave segments thereby defining a contact line therebetween which extends an entire length of the first heat transfer element and the second heat transfer element. Adjacent pairs of the contact lines define a closed passageway therebetween and between the first heat transfer element and the second heat transfer element for heat transfer fluid flow therethrough.