xxi CHAPTER 35 Humidity Control ...........................924 35.1 Humidity Levels and Comfort .............926 35.2 Types of Humidifiers ...........................928 35.3 Dehumidifying Equipment ..................934 35.4 Servicing and Installing Humidifiers ...936 CHAPTER 36 Thermostats ......................................940 36.1 What Is a Thermostat? .......................942 36.2 Types of Thermostats .........................946 36.3 Line-Voltage Thermostats ..................952 36.4 Low-Voltage Thermostats ...................952 36.5 Millivolt Thermostats ...........................955 36.6 Digital and Programmable Thermostats .......................................955 36.7 Thermostat Installation .......................960 36.8 Thermostat Diagnostics ......................964 36.9 Zone Systems ....................................968 CHAPTER 37 Heating and Cooling Loads ..........982 37.1 Heat Transfer .......................................984 37.2 Heat Loads .........................................984 37.3 Calculating Heat Leakage ...................985 37.4 Other Factors Affecting Heat Loads ...............................................1000 37.5 Heating and Cooling Load— Manual J Method .............................1007 37.6 Software and Apps for Load Calculations ..................................... 1014 Section 11 Heating Systems CHAPTER 38 Forced-Air Heating Fundamentals ................................1020 38.1 Basic Components ...........................1022 38.2 Furnace Types and Construction ......1025 38.3 Forced-Air Duct Arrangements .........1027 38.4 Makeup Air Units ..............................1027 38.5 Blower Controls ................................1029 38.6 Unit Heaters .....................................1031 CHAPTER 39 Hydronic Heating Fundamentals ................................1034 39.1 Hydronic System Components .........1036 39.2 Hydronic System Designs ................1047 39.3 Hydronic System Controls ................1059 39.4 Hydronic System Installation ............1063 39.5 Troubleshooting and Servicing Hydronic Systems ............................1065 39.6 Preparing a Boiler for the Heating Season ............................................. 1074 CHAPTER 40 Heat Pumps ....................................1080 40.1 Heat Pump Basics ............................1082 40.2 Types of Heat Pumps .......................1083 40.3 Heat Pump Efficiency .......................1086 40.4 Heat Pump System Components .....1088 40.5 Heat Pump Controls ......................... 1100 40.6 Heat Pumps and Solar Heating Systems ........................................... 1105 40.7 Heat Pump System Service ............. 1106 CHAPTER 41 Gas-Fired Heating Systems .........1114 41.1 Gas Furnace Operation Overview .....1116 41.2 Combustion ........................................1117 41.3 Gas Valves ........................................ 1121 41.4 Gas Burners...................................... 1122 41.5 Ignition Systems ................................ 1124 41.6 Gas Furnace Controls ....................... 1127 41.7 Gas Furnace Efficiency ..................... 1131 41.8 Gas Furnace Venting Categories ...... 1134 41.9 Gas-Fired Radiant Heat .................... 1134 41.10 Gas-Fired Heating System Service ... 1134 CHAPTER 42 Oil-Fired Heating Systems ..........1148 42.1 Basic Oil Furnace Operation ............ 1150 42.2 Fuel Oil ............................................. 1151 42.3 Combustion Efficiency ...................... 1152 42.4 Fuel Line Components ..................... 1157 42.5 Oil Burners ....................................... 1161 42.6 Primary Control Units ....................... 1169 42.7 Oil Furnace Exhaust ..........................1176 42.8 Oil-Fired Heating System Service .....1176