While the primary purpose of developing all-aluminium heat exchangers is to attain cost reductions, since the cost advantage of the material depends on the market price of copper, it is difficult to ensure an advantage in the total manufacturing cost. Other cost factors must also be taken into account, including changes to the manufacturing line and accompanying investment in equipment. The challenges involved in service and maintenance in the field also need to be resolved. Despite these issues and uncertainties, it seems to be generally accepted in the United States that all-aluminium heat exchangers will eventually become the mainstream. Carrier, a front-runner in this field, started adopting all-aluminium heat exchangers in its rooftop units from an early stage. It also adopts all-aluminium heat exchangers in some of its chillers. While York, Trane, and Daikin follow behind Carrier, all-aluminium heat transfer coils have become standard in rooftop units in the United States.