A Homeowner's Guide to Water Heaters

Water heating accounts for about 15 to 20 percent of the typical household energy use, only space heat and cooling cost more. So it makes sense to learn how to get the most from your present water heater and to know what is available when it comes time to replace the unit. It is a good idea to start thinking about it now because when your water heater goes, you will want to get a new one installed ASAP, which is not a good time for thoughtful comparison shopping.

Water heaters with storage tanks are by far the most common types available. They consist of a 20- to 80-gallon tank that holds the water at a preset temperature. They are fueled by electricity, natural gas, propane or oil. Electric units usually have two heating elements to warm up the water. Gas and oil heaters contain a combustion chamber under the holding tank. A flue rises up through the tank so that combustion gases can be vented to the outside. Water heaters are fairly low maintenance, but there are a few things to keep in mind.

• Temperature-pressure relief valve. This is a valve located on the top of the storage tank. It may be connected to a pipe that runs almost to the floor. The valve is designed to relieve excess pressure should it build up inside the tank. It is a good idea to test it at least once a year. When you do test it, be aware that the water and steam coming out of the valve will be very hot, so take precautions. To test, place a bucket at the end of the pipe. Lift the handle of the valve so that it is parallel with the floor. There should be a release of water and pressure. If nothing happens, call a plumber as soon as possible to replace the valve. If it works, return it to its original position.
  
• Drain valve. There is a drain valve near the bottom of the storage tank. Water heater manufacturers recommend draining off a few gallons of water occasionally to remove sediment that can build up in the tank. Turn off the water leading to the tank and the power. Follow the manufacturer's directions for draining the sediment. If the water heater is old and you have never opened the valve, it may be best to call in a plumber in case the valve leaks when you try to close it.
  
• Shutoff valve. There should be a shutoff valve on the cold water line just before it enters the water heater. If there isn't one, you will need to turn the water off for the whole house when the water heater is serviced or replaced.
  
• Anode rod. This is a long magnesium or zinc or some combination of metals that is suspended inside the storage tank. It is there so that any corrosive elements in the water will attack it rather than the lining of the tank walls. They degrade after a while, making them useless and the tank vulnerable. Have a plumber inspect the rod and replace it if necessary. It can prolong the life of the heater.
  

These have storage tanks and built-in heat pumps to boost the energy efficiency of the unit, making them over two-times more energy efficient than standard water heaters. (More on energy efficiency later.) Heat pumps transfer the heat in the air to the water in the tank. When the heat pump can't handle the load, it switches to electrical backup. They are high-tech appliances with digital readouts, built-in leak detection and wi-fi capability on some models. They are expensive—costing three or four times more than some standard models.

As the name suggests, these do not have a storage tank. They create hot water on demand. There are units that can supply the entire house with hot water, as well as point-of-use heaters that heat water at a specific location, such as a kitchen sink. Both gas and electric models are available.

They offer a number of advantages over standard water heaters. There is no need to keep water at a steady temperature of 120 degrees or so when no one is using it, so they are more energy efficient. The Department of Energy estimates that for a family that uses less than 40 gallons of hot water a day, some tankless units would be 24 to 34 percent more efficient than a standard model. And even whole-house models are fairly compact and can be hung on a wall, freeing up floor space.

Unlike standard water heaters that are rated on the number of gallons the tank can hold, tankless models are rated by the number of gallons they can heat in a minute (GPM). That makes sizing them tricky because you have to estimate how much hot water you may need at any given time.

If you do plan on installing a tankless unit, be sure to examine the product literature carefully. Tankless units are promoted at their maximum GPM. But that number is affected by the temperature of the incoming water. The difference between the temperature of the incoming cold water and the hot water you use is called the temperature rise. And incoming water temperatures vary. If the unit has to raise the temperature by, say, 70 degrees, then the unit advertised as producing 9 GPM will actually only be able to produce significantly less.

If your water heater still has the yellow Energy Guide label attached to it, you can tell how your unit stacks up efficiency-wise compared to similar models. There is a scale on the label that estimates the cost to run the heater for a year. The scale runs from least expensive to most expensive to run and your unit will fall somewhere on the scale. If the appliance complies with Energy Star criteria, that will be noted on the label as well.Energy Star is a voluntary Environmental Protection Agency program that promotes energy-efficient products, including water heaters. Energy Star products are about 8 to 10 percent more efficient than standard products.

While Energy Guide labels have been used for some time, the Department of Energy recently made some changes in the way it calculates energy efficiency. Called the Uniform Energy Efficiency rating, the new system will replace the older Energy Factor rating. The newer rating system changed the labels somewhat. The information on the labels can help you compare models. New labels will tell you:

• First Hour Delivery Rating, which is the amount of hot water the unit delivers in the first hour of operation. This will give you a sense of how much hot water you can count on when you need it.
• Capacity is listed in both the nominal tank size, 40 gallons, 50 gallons, etc., as well as the actual tank capacity.
• Estimated cost to run the water heater for a year.