Dickinson 00-HEA3 3" Heatex Stack Robber Kit. This unit installs in the flue stack of our heaters and stoves. It effectively 'robs' heat, that would otherwise be wasted up the chimney, and redistributes it to another part of the boat. It can work wonders and really expand the reach of your heater or stove. Comes with 3" heat exchanger and 12 volt fan assembly. 3" Ducting from fan to heat exchanger sold separately.