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How to Open a Lennox Furnace

Claire Gillespie

You may need to open a Lennox furnace to switch off the gas or change the gas valve setting. To do this, you simply remove the upper access panel.

How to Open a Lennox Furnace

A modern gas forced-air heating system, such as a Lennox furnace, has an automatic pilot connected to a thermostat. When room temperature drops below a preset level, the thermostat sends a low-voltage electrical signal to the furnace that opens a valve, delivering natural gas to the burners and turning the blowers on.

A standard gas furnace is comprised of a combustion chamber with a burner inside. The pilot light or electronic ignition lights the burner to create heat in the furnace’s heat exchanger, a metal cavity around which the moving air flows. As the air heats up, it moves into the hot-air plenum and then into the rooms of your home via the ductwork. The burning fuel produces combustion gases, which are vented through a flue in the roof or through a wall.

A Lennox furnace unit typically has two panels: an upper access panel and a blower access panel. It's not advisable to remove the blower access panel. If you think there is a fault with your furnace, contact a licensed professional service technician.

However, you may need to open a Lennox furnace to turn off gas to the unit or change the gas valve setting. This involves removing the upper access panel.

    Shut off Power

  1. Before taking off the panel, you must shut off electrical power to the furnace. Flip the disconnect switch near the furnace; if there isn't one, use the circuit breaker in your home's service panel.

  2. Turn the Thermostat Down

  3. Set the thermostat, which is normally on the control panel at the bottom of the furnace, as low as it goes.

  4. Remove the Access Panel

  5. To take off the upper access panel, carefully raise it and pull it away from the furnace. Set it to one side.

  6. Work the Gas Controls

  7. If you need to turn the gas control off, locate the lever or knob. If you have a lever, slide it to the "off" position. If you have a knob, turn it clockwise to the "off" position. If you need to change the gas valve setting, turn the lever or knob off. Wait five minutes to ensure all gas is cleared out of the lines. Turn the gas back on.

  8. Replace the Access Panel

  9. Replace the upper access panel and turn on the electrical supply to the furnace. Adjust the thermostat to the correct setting.

  10. Warning

    If you smell gas, leave your home immediately and call your gas company or fire station for assistance. Gas fumes can result in personal injury or death.

    Do not attempt to service your Lennox furnace; this should only be done by a licensed professional service technician. The blower access panel must be securely in place at all times during operation.