Installing a hot water heater is very easy to do. In fact, there are only two tough items in the whole process. First, finding a friend who will help you move the new heater in, and take the old one out. The second hard item is finding a place to dispose of the old water heater. Well, one trick I discovered is if you live in the north where it snows, just wait for a snowy night and put it in your neighbors front yard, the snow should cover it up for a couple of months and you can be on your way to hot water in no time.
Once you do find that friend who can help you move the hot water heater in, the rest is easy. The first thing you want to do is turn off the gas. There should be a gas valve, on/off valve on the pipe leading to your hot water heater. Turn this off. I would also suggest turning the gas off by the meter which is usually located outside. Make sure you check with your gas company that you can legally turn the gas off at the meter before you do this on your own.
Once the gas is off, you will have three places to disconnect before you can proceed. First, take off the gas line leading to the hot water heater. You might need a pipe wrench to loosen the pipe. Once you disconnect the pipe you might smell gas, and not from your friend either. This is OK because there will be some gas left between the hot water heater and the valve shut off. Just make sure you don't hear gas leaking anywhere or you don't continue to smell gas.
Once you disconnect the gas pipe, you will need to disconnect the hot and cold water. Again, you should see a shut off valve on the cold water. Turn this off. You might want to shut off the main water as sometimes these valves will not close all the way since they are rarely used. Once the water is shut off, hook a hose up to the drain valve at the bottom of the hot water heater and drain the water into a drain. Otherwise you will not be able to move the hot water heater due to the water weight. After you drain the system and you are sure the water is off, you will have to cut the copper pipes leading into the hot water heater. If you are going to replace the valve, make a cut above the valve. If you are sure the valve still works, you can cut below the valve. My suggestion would be to replace the valve either way. A valve is only a couple of dollars and you will know if you ever need to shut off the water, it will work. Now you have the gas line and water lines disconnected, you can move the old heater out and put the new water heater into place.
Now that the new hot water heater is in place, you are ready to take your measurements. Measure and cut your copper pipe for the hot and cold water. Before you start to solder, do a dry fit to make sure everything fits. If everything fits, you can solder your pipes into place. If you are unsure about soldering, it is very easy. You can read and see our soldering video on this site. Once the hot and cold pipes are in place you can replace your gas pipe. Most of the time hot water heaters are standard and you will not need to adjust the height of the gas line. If you do, your home improvement store can cut a piece of black pipe for you. Before you put the black pipe back into place remember to put pipe tape on all the threads. Pipe tape looks exactly like Teflon tape for water pipe, but is Teflon tape for metal pipes. Usually it is in a yellow container instead of blue.
Now that everything is connected, you can turn both gas valves on. The outside and inside valve. Use a small bucket of soap and with your fingers put the soap suds over the areas you connected and make sure you do not see any bubbles or gas escaping. If you do, tighten the pipe tighter. After you are sure the gas is connected correctly, you can turn on both water valves to let water into the tank. Again make sure you have no leaks. After you discover there are no leaks, you read the manual on how to light the pilot light to the hot water heater. The last item is to go have a beer, watch the game and get ready for some hot water.