How water heaters work
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.
It's easy to forget about the water heater as long as it's working, but you can extend its lifespan with periodic maintenance.
Some experts recommend draining the tank once a year. Others suggest draining one quart of water every three months. In either case, you are trying to remove sediment that slows down heat transfer and lowers efficiency. Check the owner's manual of the heater would give specific maintenance advice from the manufacturer.
If you'd rather just not deal with it, one option is to just get on a service provider's long-term calendar for annual maintenance.
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.
Relighting the pilot
Natural gas water heaters installed previous to 2002 need to be lit with a match. Look for a diagram in your owners manual for guidance, but here are the basic steps:
Remove the outer and inner doors at the bottom of the tank.
Follow the gas lines to locate the pilot.
Turn the control knob to "pilot."
Press down and hold the pilot button while you light with a match.
Keep the pilot button down for one minute and turn the temperature control all the way down.
Release the button and look to see if the small blue flame of the pilot remains lit.
Turn the temperature back up and you should see the burner ignite.
Newer water heaters are much easier to re-light because they have an electric spark generator, much like the one on a gas grill. Turn the gas valve to 'pilot' and press down. Then, press the pilot light ignition button. You should hear a click. Turn the gas valve to ON and the burner should light.
Regardless of which kind you have, if you smell gas you should not try to light it yourself. If you can open a nearby window, do so. Do not light a match or cause any kind of spark. Don't even flip a light switch. Call your gas company.
Tankless water heaters
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.
Solar water heaters
There are two fundamental types of solar water heaters.
"Passive" solar systems are used in sunny climates with very mild winters. They require no moving parts and are effortless to maintain. Household water is simply circulated in pipes through a solar collection area on the roof – much like leaving a garden hose in the sun.
In colder climates, an "active" system is used. Active solar systems use pumps to move a non-freezing liquid through the solar collection area and then through a heat-exchange area where the water is heated.
Both systems generally use conventional water heating methods as a backup or to augment the solar system. Monthly water-heating costs would be reduced, but the amount of savings would depend on the climate. A homeowner may be motivated to install a solar system primarily for environmental reasons. If the motivation is primarily economic, the homeowner would need to balance the higher cost of installing the system against the anticipated monthly savings.
When buying a standard water-storage heater, the main decision is capacity. Was your last one big enough? Has your family size changed?
Look for the Energy Star label. Energy-saving features which may make the unit cost more, but could save you in the long run. Some models may be eligible for state and federal tax credits and/or utility company rebates.
Consider alternatives to the standard tank heater such as tankless heaters or solar heaters. Both would cost more to install than conventional heaters, but may save money in the long run. Be sure to factor in how long you expect to live in your current home.