This is part one of a series of post about my solar hot water system. Make sure to follow along! I built a large water tank in my crawlspace under my home. This is a wood-framed and insulated tank connected to a solar system for heating water. The crawlspace under my house is fully inside the thermal envelope. There is an R-26 of foam board insulation at the ground level, and no insulation in the joists. So, the crawlspace is always within a few degrees of the living space