4I was fortunate to have had the late, great Gil Carlson as one of my teachers. He invented primary-secondary pumping in the early '50s and went on to do many other things. Over the years, I've watched a lot of trial and error with primary-secondary heating systems. That's a shame because guesswork costs both time and money. In this book, I've used what Gil taught me to show you how to reduce the size of your pipes, valves, fittings and pumps, and how to lower heating system temperature, and all without sacrificing performance or getting into trouble. This book covers two-pipe primary-secondary heating systems, as well as one-pipe heating systems. It shows how to get the most out of two-, three-, and four-way valves, as well as injection pumping. I also give you lots of options for your boiler-room piping (for both single- and multiple-boiler systems). It's loaded with diagrams and I went easy on the math because you may not be an engineer (and neither am I). This book will save you time and money and keep you out of trouble. It is not a primer, but it is easy to understand. - Dan Holohan