I hope some of the forum readers will share any experiance with pressurizes storage systems. I got another quote today for an open vessel 822 gallon (STSS) storage system with 3 180' coils. Those coils were $330 each when I got a quote a while back, but now they're $975 each. That makes the total bill for tank and coils around $4800, not including controls etc. There will also be a shipping fee of close to $500. It seems I can do a lot with those sort of funds in the way of pressurized storage. Question 1 - Is there any other effective means to heat an open vessel? The pair of 180' coils is rated somewhere around 11 GPM. I've heard of flat plate heat exchangers. Could this be submerged to do the job? A 20 GPM flat plate heat exchanger (I know nothing about them) can be had for $200 from pexsupply. The picture makes them look more like a "fluid in a pipe" to "fluid in a pipe" exchange. Would fintube coils (like a tankless coil) be more effective or cheaper than the plain copper coils? What else is there? Question 2 - I have not inquired locally, but a quick web search says a 1000 gallon propane tank would be around $2000. A large expansion tank would be under $1000. This is still far cheaper than option 1. Is anyone doing this? Are other tanks out there (such as various plastic varieties) rated to take the pressure? Would the high temperatures affect plastics? It is not the cost of the STSS tank that is hard to swallow, but the cost of the heat exchangers. Any ideas would be great.