In a boiler, the draft is provided either by chimney alone (natural draft) or by fans located either after the boiler (induced draft) or before the boiler (forced draft). Natural Draft: Natural Draft is provided by a chimney when hot gases pass through it. Hot gases when formed are lighter and raise up the chimney creating a suction behind them, thus allowing cold air to be drawn through. A high chimney creates a stronger draft than a shorter one. Induc