How to Insulate Your Water Heater Tank
Is your water tank new? Then it's probably already insulated. If, however, your hot water tank is old ,you should check to see if it has insulation with an R-Value of at least 24. If you can't determine your water heater tank's R-value, touch it and see if it is warm. If it is, it needs more insulation. Insulating your water heat tank can save you about 7%-16% in water heating costs!
Before you go out shopping, make sure that your water heater is in perfect working order and that it isn't leaking. A leaking water heater means you need a new one. If your water heater is in good condition, check with your utility to see if they offer materials like water heating insulating blankets at a discount or a low price. Some utilities even install these at little or no cost. Be sure to start this project at a time when someone else can help you, because you do need two people.
You will also need:
-a tape measure
-water heater insulating blanket kit that includes electrical/other tape
Once you have assembled all the supplies, you need to turn off your water heater. An electric heater can be turned off by turning off the breaker in the electric panel. A gas water heater can be turned off by turning the gas valve to "Pilot".
Now, it's time to measure the height of the water heater. Leave the top of the heater open so the vent on top of the gas unit is unobstructed. Cut the insulating blanket according to your measurements.
Wrap the blanket around the water heater and tape it into place for now. Try to make sure that the ends of the blanket do not reach together on top of the access panels on the side of the tank.
Use your marker to mark off the areas where controls are so you can cut appropriate holes into the blanket. You should also mark where the pressure relief valve and pipe are (the pipe that sticks out of the side of the water heater.
Now, carefully line up the cut out areas and tape the blanket permanently into place. Mission accomplished! You can turn the water heater back on! If you have an electric water heater, be careful not to set the thermostat over 130º F as the wiring may overheat with the insulating blanket on.
Referenced from Energy.gov