Caleffi’s 17th edition of idronics is titled “Thermal Storage in Hydronic Systems.” Because of the excellent heat storage characteristics of water, adding thermal storage to a hydronic system lends itself well to many benefits including buffering a heat source against short cycling, reducing the heat source size relative to peak load and optimizing the use of surplus heat production. This edition explores these benefits and discusses how to properly apply thermal storage in hydronic systems. The edition is available free online.