So iv been in the trade for 3 1/2 years, have been going to school the whole, time, and I'm in a HVAC apprenticeship. BUt we haven't touched this subject yet, and its kind of making me struggle out in the field, when I take boiler, or air flow calls. Please guys, i need help understanding this 101. please. Does anyone have some advice, rule of thumb, or classes they know of in the west coast that could help me. Websites, and books help as well.