I need more hot water. I currently have a sidearm for my hot water on my owb. I am wanting to get a flat plate exchanger, I called my boiler dealer and he quoted a 30 plate for about $350. What's the difference between his and ones on eBay for half of that price? What should I look for in a flat plate? I would also like to see some pics of some installed and of the valves installed to clean it out. Any advice would be appreciated.