A simple underground PVC pipe, often called an "earth tube" or "ground coupled heat exchanger" can potentially reduce your cooling bills by using the earth's near constant temperature to precondition outside air coming into your home. The same system can be used to reduce heating costs in the winter. This method is a low-tech solution that works on some basic physics, but just because it is low tech does not mean that some thought, planning, and design are not needed.
Mark the route for your ditch with stakes and string or survey marking paint. Mark the ditch a measured distance to the side of where you will dig, so that you do not disturb the mark while digging. The ideal route is a straight, slightly downhill run about 100 feet long.
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Dig the trench. The depth of the trench will vary based on your area and the desired efficiency of the tube.
Fill the bottom of the trench with pea gravel to a depth of 2 to 3 inches. This will level the bottom of the trench and provide a drainage layer that will reduce the chances of water getting into the pipe.
Install the pipe using PVC primer and cement to seal each joint in the pipe.
Cover the end of the pipe that is open to daylight with the insect screen and chicken wire to prevent rodents and insects from entering the tube. This screen should be removable to provide access for cleaning.
Back fill the trench. Cover the pipe with 1 to 2 feet of dirt before replacing any large rocks so that the pipe is not damaged.