The life of a conventional storage water heater is generally determined by the tank, which usually rusts through within 10 to 15 years, thus calling for a replacement. (Source #1)

Previously, tanks were made of copper, were very resistant to corrosion, and could last decades. They are now made of glass- or porcelain-lined steel, and can rust and leak. Sacrificial anode rods made of magnesium or aluminum alloy are installed in these to help prevent this. These rods undergo galvanic corrosion to reduce corrosion of the steel tank. The longer the guarantee on a tank, the more anode material in it. The tank will rust, however, when the anode is used up, although you may be able to check the anode, and, when needed, replace it. (Source #2) These should be checked and probably replaced every five years, which is the life expectancy of the anode rods. (Source #1)

Plastic tanks are available in some electric water heaters. These are designed with materials that are corrosion-free and corrosion-resistant. They could, in theory, last as long as the home.

Regular (at least annual) maintenance of conventional storage water heaters involves draining the bottom of the tank of accumulated sediment, helping to maintain efficiency and extending the life of the tank. (Source #2)

Below is a brief, helpful summary of the five main types of water heaters available, based on information from the Department of Energy. Future articles here will provide more specifics about each type.

1. Conventional storage water heaters

This type of water heater has a storage tank full of (usually) ready-to-use hot water.

2. Demand water heaters (also called tankless or instantaneous)

These heat water on-demand; no storage tank is required.

3. Heat pump water heaters

Heat pump water heaters take heat from another source, such as the surrounding air, and put it (at a higher temperature) into a tank where it will heat the water.

4. Solar water heaters

Obviously, these heat water with heat from the sun.

5. Tankless coil and indirect water heaters

This type heats water using the space-heating system in the home.

(Source)

Heating water in a home, on average, uses 13% to 25% of the energy consumed in that home. Depending on your source of information, it is the second (1) or third (2) largest consumer of residential energy, being topped only by space heating and cooling, and possibly by kitchen appliances.

A number of factors should be considered when choosing a water heater, including (but not limited to) energy efficiency; type of fuel and its cost and availability in your area; size/capacity; cost, taking into account the purchase price and the cost of installation; and the space you have provided for the system. Your climate and environment, including the position of your home, should also have an impact on your choice, particularly when considering a heat pump water heater, a tankless coil water heater, or a solar water heater. Another factor is ease of installation: will this be in a new-construction or is it a retro-fit?

Among the types of water heaters available today are storage, or tank-type; tankless; demand (or instantaneous); heat pump; natural gas; propane; oil; electric; and solar, each type having its own advantages and disadvantages.

Future posts will examine the types of and considerations about water heaters in more detail.

1. Source
2. Source