Comfort Shield is designed to provide coverage beyond the standard manufacturer's limited warranty., COMFORT SHIELD HOMEOWNER TERMS AND CONDITIONS. How do you read a Lennox serial number for a year? Trane warranty registration is quick and easy. Also available on our mobile app. With the LennoxPros app, looking up warranty information on the job site is fast and easy. On average, Lennox air conditioners can last for 15 to 20 years. We provide free shipping & factory warranty on everything we sell. The serial number for your Lennox air conditioner is printed in black on a white background on the data plate, or nameplate, which is found on the unit's exterior near the service panel. We provide free shipping & factory warranty on everything we sell.