A conventional tank water heater heats a large amount of water all at the same time and then expends energy to keep it hot until it's needed. Tankless water heaters operate on a different system. They only use energy when you use hot water. If you use your hot water wisely, your new tankless water heater can save up to 50 percent the energy it needs to heat water. A tankless water heater is smaller than an old-fashioned one, and is usually fastened to a wall. Installing a tankless water heater yourself can be difficult, but if you are good at handling power tools and solder, you can do it yourself.
Shut off the water to your current hot water heater. Drain the old water heater with a water hose and remove it.
Route the hot and cold water lines to the location where you will put your new tankless water heater. If the pipes aren't exactly where they need to be, you will need to cut the pipe with the pipe cutter and solder on new copper pipe.
If you have chosen a gas heater, solder the proper size of gas pipe to the location where your tankless water heater will be. Closely follow the instructions that come with the water heater. If you chose an electrical heater, install the wires needed to the unit location. Install the proper size circuit breakers, as shown in your installation manual.
Bolt your tankless water heater into place in the location you have chosen. Use the bolts provided and a wrench, following the instructions that come with the heater.
Connect the water pipes. For your gas heater, install a 5 inch or larger B vent. The vent needs to be extended above the roof for 5 feet or more.
Install the pressure and relief valve into the heater, following instructions in the installation booklet.
Turn off the electricity or gas if you have a gas heater, and run several cycles of water through the heater until the water coming out runs clear.
Adjust the knob or other device on your heater to the temperature you want your hot water to have.
Turn the water and the electricity or gas back on, open a hot water faucet and watch the hot water come out.