Hi , thanks Doug and Russ , we got it going today and had to make a few adjustments , took out the fancy aluminium burner and replaced it with a $ 10 cast iron frypan , same as i use on the shed heater, we use half a cup of what we call Angel Juice to get it running , was given a 200 litre drum by a company that services portable generators , they said the drum was a mixture of waste oil , kerosene , diesel and petrol , i was reluctant to use it as the primary fuel and decided to test it as a starter fuel and it will burn for a good 20 mins , we run the drip valve at about 3 drops a second for about 30 mins and the turn it up to a fine stream, the heater was boiling the water in the coil before it had a chance to run back to the pool so the no pump and natural convection idea was a dead duck , we shut it down and re plumbed it so the water is pumped around the heater and its alot safer , the return fitting is about 3 inches below water level so its easy to poke a hand in to get an idea how the heater is going, a few facts , the pool is 1500 litres , start water temp was 18c ( 64.4F) it took 4 hours to bring it up to 40c (104F) which is about 30 mins faster than the timber , i estimate that i may only have to run the heater for say an hour a day to maintain temperature, the heater uses about 1.5 litres per hour, i did a deal with a guy and got a 600 litre header tank , based on my figures it will keep me going for a while , i will try and add a picture of the set up, will add a roof to keep the weather of the heater and maybe a little concrete pad for it too , feel free to ask questions , Regards Kevin