How to Install a Lennox 15GCSX

Check that your unit is configured to use natural gas or propane, according to your supply. The internal governing and jetting is different for the two fuels, and the two are not compatible.

Select an outdoor location where unobstructed airflow can reach the condenser coil. The unit cannot operate safely with insufficient combustion air; this is drawn in through the condenser, which must not be obstructed in any way.

Minimum clearances are 36 inches in the front; 48 inches rear; 24 inches left-hand-side; 30 inches right-hand-side; and 36 inches top. A prefabricated pad must be available, no less than 4 inches thick and a minimum of 6 inches greater on each side than the dimensions of the unit. The pad must be no more than a 1/4-inch off-level across its greatest dimensions, and be without sagging, cracks or gaps.

Minimum clearances for the vent outlet are 4 feet horizontal distance from any door, window or other air inlet; and 4 feet below or 1 foot above the same.

Position the unit on the pad. The 15GCSX is heavy, so have assistants help you maneuver the unit off its delivery pallet and into place. Double-check the clearances as noted above. The unit does not require mechanical fastening to the pad.

Turn off the electrical disconnect switch that serves the installation. Make the electrical connections per manufacturer instructions and any advisements from your local code enforcement office.

Consult the current National Electric Code ANSI/NFPA No. 70 to determine wiring temperature limits and gauge, as well as grounding requirements. The electrical wiring entry is at the top right-hand corner of the unit when looking from the rear.

Make the gas connection from a natural gas line fitted with a stop-tap or a properly governed propane line. Consult the current National Fuel Gas Code Z223.1 to determine minimum pipe diameter. The gas line entry is at the top right-hand corner of the unit when looking from the rear.

Connect a condensate drain line according to local code. Such drains should fall into an unobstructed open drain, and be supported to relieve the connection of any pull. The condensate outlet is toward the bottom of the rear of the cabinet, near the left-hand side as viewed from the rear.

Connect the building’s interior thermostat to the unit, making the connections according to manufacturer instructions. The thermostat wires are color coded, and a terminal wire color chart sticker should be located inside the main inspection panel on the front of the unit.

Inspect the return air duct to confirm it is sealed along its entire length. Check that the air filter in the return air system is correctly oriented; air flow direction is printed on the filter frame. The motors in the 15GCSX are all permanently lubricated and do not require any attention in the installation procedure.

Visually check that no dirt or debris has collected on the furnace burners or the surfaces of the A/C coil during storage, transit or installation. If the coil is not completely clean, use a soft brush vacuum cleaner attachment to remove the contamination. The fins are fragile so take great care not to damage them.

Turn on the gas stop tap. Use your hand only, not a tool, and have a qualified service engineer adjust the tap if it cannot be opened and closed by hand. Use a pressure gauge -- properly called a manometer -- to test the gas installation for soundness. Follow the gauge manufacturer’s instructions to the letter. Reinstate the electrical disconnect switch that serves the installation.

Allow the unit to go through its ignition sequence. The 15GCSX series has an automated spark ignition system and does not require the installer to ignite a pilot light. If the system does not ignite, try resetting by moving the switch on the thermostat to “Off” and then back to “Heat.”