This article is a case history of an addition to an existing house. The project was designed and built in 1995–1996. It presents a practical engineering analysis intended for fellow practicing engineers. The article explores the design criteria and analysis that led to the choice of a hybrid (in-floor radiant/baseboard) hydronic heating system for the addition. After describing some coordination and installation considerations for various in-floor heating designs, it presents measured performance data from a side-by-side comparison of radiant and baseboard heat on the project. The article concludes with a summary of lessons learned and what in-floor radiant heat can and cannot do.