Why

Half of the natural gas used in a typical home in this region is used for heating water. Installing a tankless water heater can save you 30-50% of that water-heating energy. Tankless, or "on-demand," water heaters are more efficient than standard tank systems since they only heat water when it is needed; standard water heating systems must keep an entire tank-that's typically 40 gallons-of water hot 24 hours a day.

Recommendation

Use gas tankless water heaters instead of tank or storage heaters. These heaters can be used in all types of buildings, but are most effective in homes. Hot water use in most commercial buildings is a relatively small fraction of total energy consumption.

Description

Tankless water heaters have been around for years, but earlier models were smaller "point of use" units designed to serve one faucet or appliance. These units had relatively small burners.

On-demand water heating technology has progressed quite a bit in recent years. The new generation of tankless (also called "instantaneous" or "flash") water heaters can meet the hot water needs of an average house (up to 7 gallons a minute).

Instead of heating a lot of water slowly, tankless heaters heat a little water very quickly. That's why tankless systems require a much bigger gas burner. A typical tank water heater uses a 35,000-40,000 BTU burner; a typical tankless water heater requires a 125,000-200,000 BTU burner. These large burners use fuel quickly, so tankless water heaters usually require a larger-than-normal gas line. For the same reason, the flue (exhaust pipe) must also be larger. A typical flue in a residential tank water heater is three to four inches; tankless water heaters typically use a five-inch flue. While the need for larger gas line and flue is not a concern in new construction, it can add extra costs in a retrofit situation.

Modern tankless water heaters work well with solar water heating and recirculating systems. Most are thermostatically controlled, which means they are designed to register incoming water temperature and apply heat as needed to reach the desired output water temperature.

Many tankless water heaters come with remote controls. Because the heating is instantaneous, you can adjust the temperature setting to suit your immediate needs. If you like 110° showers, why mix cold water with 120° water? With the remote control, you can set the temperature to exactly the desired temperature.

Tankless water heaters are relatively small, offering greater design flexibility with more placement options and freeing up the space that would have been required for a tank heater for other uses. They do not require the seismic strapping of tank heaters, and if placed in a garage, they are not required to have bollard (metal pipe) protection from vehicles, as tanks do.

Gas, propane and electric tankless water heaters are available. Electric should be avoided as an extremely inefficient use of energy.

Concerns

People will use more water. Tankless systems save energy only if your hot water consumption stays the same. Unfortunately, some tankless hot water heaters are advertised as "endless water heaters." If everybody in your household starts taking endless showers-the benefit is obviously lost. What's worse, you'll see the bad news on your water bill as well.

Tankless systems don't like our hard water. The water in Ventura County is generally hard. When hard water is heated to very high temperatures, minerals precipitate out and build up on the inside surface of the heater. Tankless water heaters should be fed with soft water or regular maintenance to remove the scaling will be required.

Lag time. Tankless water heaters do have a slight lag time, because it takes a few seconds for the heat exchanger to get up to temperature so it can transfer heat into the water. Other equipment can be installed to address this.

Design Details

Install the tankless water heater as close to the points of use as possible, and adjacent to an exterior wall or roof to reduce the cost of venting (stainless steel venting is required). Exterior-mounted units are also available; these don't require venting but must be located at least eight feet from operable doors and windows.

The device should be appropriately sized and have a control that allows the hot water temperature to be varied.

Look for a plumber with experience installing tankless water heaters.

Other Ways to Improve Water Heating Efficiency

Replace Your Old Water Heater: If a tankless water heater isn't right for you, consider replacing your older tank heater with a more efficient one. Look for water heaters with an Energy Factor of at least 0.60.

Insulate Your Hot Water Heater: If your water heater tank feels warm to the touch, you're wasting energy. Wrap an insulation blanket around the tank.

Insulate Your Hot Water Pipes: Most heat is lost from pipes close to the water heater (within six feet), where the temperature is being maintained at the water heater's set point. The higher the temperature, the greater the heat loss through the uninsulated pipes. Insulate all accessible hot water pipes with a minimum of one-inch insulation. Foam pipe insulation is very inexpensive and easy to install. Insulating hot water lines is also likely to add convenience, comfort, and water savings.

Lower the Temperature: Set the temperature of your water heater to 115-120° F. Newer dishwashers should have their own heater to boost the temperature for extra cleaning. When you leave on vacation, turn the water heater way down.

Use the Sun to Make Hot Water: Solar water heating systems have advanced significantly from earlier models. These systems pay for themselves in just a few years. Learn more about solar water heating.