How to Replace the Heat Exchanger in a Gas Pack

Disconnect the thermostat leads and the combustion-blower wires. Remove the screws from the combustion blower, then remove it from the furnace. Repeat the steps to remove the main blower, disconnecting the leads from the control box.

Disconnect the upper switch leads. Remove the blower shelf by unscrewing it from the casing. Remove the coil cavity cover by unscrewing it from the casing.

Lay the plywood on the coil and brace it with the wood planks to hold the heat exchanger in place as you work. The wood braces need to be long enough to hold the plywood in place; this length will depend on the height of your specific furnace unit.

Unscrew and remove in order: the combustion air pipe and flue pipe from the top of the furnace casing, the divider plate, the combustion air pan, the combustion air vane, the burner chute and the vestibule panel. The divider plate screw heads will be on the outside of the furnace casing.

Take out the wood braces and remove the plywood with the heat exchanger.

Place the gasket from your new heat exchanger on the flue collar. Set the new heat exchanger on the plywood and place it in the furnace casing. Replace the wood braces to hold up the exchanger, while you replace the screws and screw the heat exchanger to the flue collar.

Seal the burner-opening gasket to the back of the vestibule panel, using the silicone. Replace and screw in the vestibule panel to the furnace casing. Connect the heat-exchanger burner opening to the vestibule panel. Remove the wood braces and plywood.

Replace the parts you removed from the furnace opposite the order in which you removed them. In reverse order the parts are: vestibule panel, burner chute, combustion air vane, combustion air pan, divider plate, flue pipe, combustion air pipe, coil cavity cover and blower shelf. Reconnect the upper switch leads. Replace the main blower and combustion blower, then reconnect both blowers and the thermostat leads.