The Karcher HDS 1000 BE/DE Coil (4.680-080.0) is unequalled in the industry for its high heating performance, compact design, and super-efficiency. Double-wall construction—with air passing between the two walls—provides insulation as well as oxygen for the combustion process.The combustion chamber and heating coil provide even heat distribution with very little condensation or corrosion and 92%+ fuel efficiency to conform to the strictest air quality standards.