HAVEWO

I currently have a 6 person spa over 25 years old in the ground surrounded by concrete on my back deck area. It is starting to crack, loosing water and have decided to upgrade to a above ground spa. I can obtain cheaplly a Hurlcon 120 gas heating unit and can obtained a 8 year old 6 person above ground spa. Firstly can anyone give me a idea how to remove the old inground spa?? Secondly has anyone totally removed the electric hot water system in a spa and replaced with a gas system to heat the spa??? Just a matter of re plumbing the pipes?? Thirdly I have tried ebay for ages now just to find a spa shell to hook the gas system too. So maybe you know where I can get a good second hand shell? Thanks HAVEWO