A combined space conditioning or heating and fluid heating system includes a main fluid conductor having an inlet and an outlet; a single heating source configured for producing low and high temperature fluid outputs of a fluid input received at the main fluid conductor inlet; a coil comprising an inlet and an outlet; and a supplementary fluid conductor comprising a fluid mover and a directional valve, an inlet and an outlet. The inlet of the main fluid conductor is adapted for connection with the coil outlet. The high temperature fluid output is adapted for connection with the supplementary fluid conductor inlet, the supplementary fluid conductor outlet is adapted for connection with the coil inlet. The low temperature water output is adapted for connection with a fluid delivery point. The water coil inlet is adapted for connection with a raw fluid supply.