Lennox 11W00 Replacement Piston. Lennox goal is to provide contractors with high-quality HVAC solutions and replacement parts. This system includes changes and inventory updates to ensure peak performance. Lennox has a large line up parts and products for high-efficiency packaged rooftop units, split systems, HVAC controls, furnaces and indoor air quality products. This Lennox 11W00 Replacement Piston is a replacement part for Ducane 2.5 Ton Outdoor Air Conditioners.