Earth tubes (earthtubes, or earth-air tubes) are underground tubes that use geothermal energy to cool or heat temper the air for your home. It works like cheap air conditioning because you can build it yourself for several hundred dollars and it is FREE to run (no electricity needed). Being completely passive, this is a sustainable technology based on designs that are 3,000 years old and still used today around the world to cool homes. TABLE OF CONTENTS (chapters, sections, page numbers): Introduction 15; Who Invented Air Conditioning? 15; How Earth Tubes Work Like an Air Conditioner 18; The Cost of Earth Tubes vs Air Conditioning 19; Background and History of Earth Tubes 23; How I Learned About Earth Tubes 23; Qanats - 3,000 Year Old "Earth Tubes" 24; Effective Use of Earthtubes 34; How Earthtubes Work 34; Convection Brings Cooler Air Inside the House 36; Evaporation and Condensation 38; Best Material for Earthtubes 41; Interior Thermal Mass Enhances Earthtubes 43; How Many Earthtubes Do I Need? 48; Making the Earthtubes 55; Parts Needed to Make One Earthtube: 57; Tools Needed 57; Earth Tube Checklist 59; Trenches 63; Possible Limitations to Digging Trenches 66; Placement of Trenches 68; Laying the Earthtubes 73; Dealing with Elbows 74; Earthtubes - Outside and Inside 80; OUTSIDE: Protecting Earth Tubes 80; INSIDE: Floor Registers and Side Vents 84; How to Make Earth Tubes Work 93; Ready Your Earth Tubes for Use 93; Treating Earth Tubes Problems with Ozone 94; Summer Use (Air Conditioning) 97; Slow vs Forced Air Flow 103; Weatherizing for Fall/Winter 105; Winter Use (Heat Tempering) 108; A Lesson on Air Quality 114; Adding Earthtubes to an Existing House 121; If you have a Large Front or Backyard 121; Attaching Earth Tubes from Outside 125; Supplemental Uses and Related Ideas 130; Using Earthtubes for a Pantry/Storm Shelter 131; Spiral Earth Tubes for Tight Spaces 133; Spiral Tube Water Catchment 134; Earth Bermed & Earth Sheltered Homes 135; Cave houses & Rock Homes 138; Roofs of Earth, Water, & Air 141; Key Principles on Energy Efficiency 143; Trees and Shrubs 146; Chimneys for Ventilation Draw 147; Solar Chimneys 149; Cooling Tower 153; Earth Lodge & Weathervane Venting 155; Other Designs 161; Bill Traub Witnessed These Earth Tubes 161; Indoor Air Quality 165; Example of Bad Air Quality from Earth Tubes 174; Calculations for Earth Tubes 179; Q&A for the Tubes 180; On the Subject of Earth Tubes 180; Olan Volan's Earth Tube Calculations 181; Tube Diameter 181; Tube Depth 181; Distance Between Tubes 181; Simple Math Calculations 182; Air Transfer 183; Pressure Differences 184; Some Notes on the Calculations of Tubes 184; Earth Tubes Q&A 186;