A hydronic air handler installs in the home and connects to the ductwork to provide heating and / or cooling (optional) indoors. The air handler is completely preassembled, and consists primarily of a multi-speed or variable-speed fan, built-in heat exchanger, and electrical controls. Depending on the model, they can be installed vertically, horizontally or in a downflow orientation. To provide heating, hydronic air handlers must be connected to a hot water source such as a tankless water heater. For these air handlers to provide cooling, a seperate outdoor condenser must also be installed.