In a first aspect, a vehicle HVAC system includes: a housing that defines at least first and second air conduits to a vehicle interior compartment; and at least first and second heat rods that each traverses the first and second air conduits, wherein a first positive temperature coefficient along a length of the first heat rod is greater at the first air conduit than at the second air conduit, and wherein a second positive temperature coefficient along a length of the second heat rod is greater at the second air conduit than at the first air conduit.