This Help students to understand the concepts of convection currents with this very visual demonstration. Place a lighted candle under one chimney, then use a smoke source over the other chimney to reveal the flow of convection currents. 

The consequences of ventilation can also be shown by covering the chimneys and removing, in various combinations, the corks in the side panels. 

The apparatus consists of a metal box with a glass front panel, two chimneys, a candle and complete instructions.