Residential solar combisystems provide domestic water heating and some percentage of space heating. Although less known than domestic hot water-only systems, combisystems can be practical and efficient if properly sized and designed.
During the first solar era in the United States, solar combisystems were designed to provide a high percentage of the space-heating load, even in marginal northern climates. Roof tops were covered with collectors and basements housed 1,000 to 2,000 gal. storage tanks. Eventually these systems proved to be “solar monuments” rather than practical, repeatable solutions. They gave certain well-healed owners bragging rights and qualified for government subsidies while they were available for the taking.