The main reason I got this book was to help me size a furnace for the house and calculate the size of the duct system. I only partially got what I needed. The examples for duct sizing started well, but fizzled out as it did not show how to include the effects elbows and other attachments in the calculation and is also missing other pertinent information. Interestingly enough, the discussion of Duct Sizing started in Volume 1 which I got from the library, but the juicy stuff was postponed to Volume 2 which I purchased, and perhaps the end of that discussion appears in Volume 3, which I am not going to purchase. This seems to be a business driven decision which I found quite distasteful. A well written book should self containing as much as it can be helped. Also lacking is a good discussion on more modern two stage furnaces and thermostats. Pages dedicated to Mercury thermostats are a bit outdated, maybe by 50 years. For a free duct calculation site try: [...]