Abstract: A method of connecting a heat exchanger to a forced air furnace is described. Firstly, connect a valve to the hot exhaust gas outlet of a furnace. The valve has a generally "L" shaped valve body. The valve body includes a primary passage. A diversion passage intersects the primary passage. A diversion return port intersects the primary passage downstream of the diversion passage. A butterfly valve member is pivotally mounted at the intersection of the primary passage and the diversion passage. The valve member has a first wing and a second wing. The valve has an open position and a closed position. The valve member is normally in the open position. Secondly, connect a fresh air outlet of a heat exchanger to a fresh air inlet on the furnace.