Sep 17, 2003 · The models heretofore most commonly found on sailboats, the D1LC compact air heater and D3LC, have been replaced by the Airtronic D2 Air Heater, which produces 2,000 Btu to 7,500 Btu in “boost” mode, and the Airtronic D4, which doubles the Btu output. The D2 weighs only 6 pounds; the DS 9.9 pounds.