The only time my oil burner runs if for hot water. The house is heated 100% with the wood stove. It is a tankless system with an expansion tank and we have baseboard heat. Would it be more economical to have storage for the hot water? The boiler runs during the day just to maintain hot water and then runs again for showers etc. I am planning building something solar this winter or at least getting it laid out and finish gathering materials but there has to be a fairly simple solution to at least assist the boiler in heating the hot water. As simple as a well insulated 55 gallon plastic barrel?