Bestway heater and filter pump, seen lots of reviews saying they dont work but ours absolutely does! Gets it lovely and warm but does take about 48h to do so. Once warm it will stay warm however heater/filter need to be running at all times so electric can be costly although I've not found it too bad. I am actually running both off extension leads, despite someone above saying you cannot, but they are on separate ones and both have overheat cutoff capabilities. I am very very happy with the setup and cant complain! Our pool is around 3500 litres and I should add that the heater will not work without the filter pump, all it does is heat water that needs to be pushed through it by the pump. But honestly I wouldnt have the pool set up without the filter anyway, gets pretty grimy also dont forget your chemicals x