Create horizontal or vertical displays using the collector & separate tubes, The collector is water filled & conducts heat through the specially designed tubes, The tubes are not water filled & can be added & removed easily, Change the layout any time to create a new design, The number of tubes you will need to purchase depends on the width of your Collector, Collector (W)430mm suits 7 Tubes, (W)610mm suits 10 Tubes & (W)790mm suits 13 Tubes, Freesystem Tubes are available to purchase in 3 different sizes on diy.com, This radiator has a low water content making it more energy efficient (faster warm up time)