There is disclosed a heat exchanger for use in a heating unit and more particularly for use in a fireplace. The heat exchanger comprises a hollow body of pleated or corrugated metal material to enhance the heat exchanger from a high concentration within the body to a lower concentration exteriorly thereof. The use of a corrugated metal material avoids mechanical fatigue since the corrugation permits easy contraction and expansion which normally occurs during heating and cooling of the heat exchanger. The result is a long-lasting highly efficient heat exchanger.
