The Oase IceFree 20 keeps an area of your pond free of ice to enable fermentation gases to escape. Utilising a small water pump (420lph) and an ingenious polystyrene float this prodcut keeps part of your pond free of ice whilst consuming only 5W of power!! The IceFree works by pumping the warmer water at the bottom of the pond to the surface to create sufficient wate rmovement to prevent freezing. Comes with a full Oase 3 year guarantee and at a low running cost saves you considerably more than conventional pond heaters