Angie's LIST Guide to
Water heaters

Although much more efficient than they used to be, most water heaters still work they same way they have for generations -- by keeping a giant pot of water piping hot just in case you need some.

Cold water is piped in through a long tube (called the "dip tube") to the bottom of the tank where it is heated by a gas or electric burner much like those on your stove. The warmer water rises naturally and is drawn out of the top of the tank as needed.

Because the tanks are made of steel they are prone to rust and corrosion. A sacrificial "anode rod" is inserted into the tank to attract oxidizing agents to itself instead of to the tank walls.

The size of the water storage tank can range from 20 gallons to 80 or more, but 30-40 gallons is typical for a single family. If this supply is used up too quickly the hot water taps will go cold until more water can be heated.

No hot water: Check the pilot light. You can re-light it yourself (see instructions on this page), but this can be dangerous so it's best to have someone with experience do this.

Water not hot enough: Check the gauge on the water heater (photo), but only turn it up one notch at a time and then test later that day. You could scald yourself if you push it up too high. If it's already set on high and the water still isn't hot enough, it's time to call a plumber. The problem is sometimes a faulty "dip tube" (which brings cold water into the tank).

Hot water runs out too soon: Did one of your kids recently become a teenager? Usually running out of hot water just means the capacity is too small for the hot water activity going on in the house. Are more people living there now or a change in habits?

Making noises: Because sound is magnified by the metal pipes, water heaters can start sounding like they are possessed by evil spirits. These noises may start and stop with water usage. If the problem persists, call a plumber.

A tankless heater provides hot water on demand and could be a better choice for households in which no one is home for much of the day and hot water usage is confined to certain hours.

How does it work? As water is drawn, it is quickly heated by high-powered burners within a heat exchanger system of coils. Does it save on energy costs? Definitely, but not necessarily enough to earn back the larger investment anytime soon.

Tankless heaters typically cost two or three times as much as a standard tank heater. Depending on your household's water-usage habits, you may save enough to make the investment pay off.

Although tankless heaters theoretically can provide an endless supply of hot water, that doesn't mean they can always keep up if two people are showering and you decide to run the dishwasher and washing machine at the same time. The tankless heater can only move water through its pipes so fast. And don't assume that a tankless heater provides "instant" hot water. Just as with standard heaters you still need to run the water long enough to clear the pipes before the hot water gets to you.

Read more: The issue of tankless vs. standard sparked a lively debate on the Angie's List Answers forum. Read the thread on tankless heaters and join in the discussion.