Location

Gas tankless hot water units can be designed to provide hot water to the whole house or as described previously, the designer can divide the fixtures and appliances which require hot water and locate the units in several locations throughout a house. The design professional should analyze the location of each faucet, fixture and appliance to determine which strategy would be the best for saving plumbing runs, saving water, and maximizing the efficiency of the tankless hot water heater system.

Indoor units can be placed in closets, under sinks and as well as in attics as long as there is access to an outside wall for ventilation. Units can also be placed outdoors. In a cold climate, manufacturers recommend that heat trace be placed on the exterior piping. Outdoor units or units placed in seldom-used vacation homes can be protected from freezing at temperatures as low as minus 30 °F. In extreme climates an automatic drain valve should be installed to eliminate freezing of the water supply in the event of a power failure. Specify testing of the drain valves as part of the installation sequence in cold climates.

Water Quality and Maintenance

Water quality is an important consideration that can be overlooked for both tank and tankless water heaters. Mineral deposits or scaling with all water heaters can lead to inefficient performance and shorten the life of the unit. As previously noted, about 85 percent of the United States has hard water, and designers can consult with the local water company for hardness ratings.

 

About 85 percent of the United States has hard water. This designer specified a water softener and water filter in conjunction with the tankless hot water heaters in this garage installation. Photo courtesy of GE Appliances

 

 

All manufacturers require the use of a water softener if the water is 11 grains per gallon or higher. Many manufacturers even make this a warranty requirement. According to the Water Research Council and Water Quality Association, soft water results in less scale build up in water heaters and up to 25 percent less energy consumption.

If a water softener is not installed, most units can also be "flushed" out with a vinegar wash which will extend the life of the system particularly in homes with hard water. This will usually require the help of a service technician since a pump is needed. The control components, compartments, burners and circulating air passageways should always be kept clean. The water inlet filter can be cleaned by first removing power from the unit and then brushing the filter with a small brush. If scale is visible, it can be cleaned in a white vinegar solution. Keeping the unit free from dust will maximize its life span and efficiency. All manufacturers will provide maintenance information to the homeowner.

Integration With Passive Solar

Tankless hot water heaters can be used in conjunction with solar hot water heating to increase the supply of hot water at higher temperatures. By supplying the units with water already pre-heated by the sun, fewer BTU's are required to raise the temperature for residential use. This combination allows for even greater efficiencies and energy cost savings. Some designers are also using tankless hot waters as part of a whole house radiant heating system tied in with solar hot water panels. In these installations, the designer connects the water supply to the solar panels which heats the water to the solar temperature and then stores that water in a supply tank. The tank is compartmentalized to create a closed loop system for radiant floor heating and there is a burner which maintains the heating source to a set temperature. In cold climates, the design professional can vary this temperature depending upon the demand for heating in the winter, lowering it in the summer.

The gas tankless hot water heater is then installed as a component above the closed loop system, to raise the temperature of the preheated hot water for use in the domestic hot water supply. This increases the efficiency of the entire system, since only enough energy is required to raise the temperature an additional 10 degrees to 30 degrees as needed by the homeowner.

Conclusions

Energy use in a home is divided into many components and according to the U.S. Department of Energy water heating is a large portion of the energy pie. The homeowner often asks the designer whether the initial cost of a unit will provide long term savings. With rising fuel costs, any appliance which reduces energy use will save money. The DOE provides guidelines as to how to assess the payback period of energy-efficient water heating systems. The design professional can also compare the cost of reduced plumbing and square footage savings to guide the homeowner to the best choice for their project.

There are many checklists for determining which green solutions are right for a project. Sustainable design-build consultant, Kathleen O'Brien, lists tankless hot water heaters as a top-ten green home tool pick in her book, the Northwest Green Home Primer. She recommends that homeowners reduce water consumption and save energy by installing these efficient cost saving devices. She points out that although the storage tank water heater has been the standard for many years in American homes, that there is an alternative which is now available to designers and to homeowners. "One danger with on-demand water heaters is that the supply of hot water is endless. If you have teens, you may not want to go this route!"⁶ Designers continue to find ways to make homes more energy efficient. Organizations such as the Energy Efficient Codes Coalition (EECC) have been formed to mount a comprehensive, integrated campaign to achieve a 30 percent increase in residential energy efficiency. Nationally, mayors of many cities are encouraging code officials to support broad-based changes in the model residential energy code. Energy savings result from both tightening the building envelope, but also from reducing the energy required to maintain comfort. ENERGY STAR^® appliances are considered one of the best ways to guarantee that a product will save energy dollars. The inclusion of gas tankless hot water heaters as a qualified ENERGY STAR-labeled product will recognize this product as a means to conserve water and energy.

The American Institute of Architects provides a list of 50 ways to "green" a building. This list was developed by numerous green designers to provide guidance on simple means to achieve energy savings and it is part of the extensive 2030 toolkit created by the AIA to show architects how to "Walk the Walk" of sustainable design. "The strategies were selected to provide a list of readily effective tools and techniques that will have an effective and immediate impact on the architects' ability to achieve significant carbon reduction.⁷ When combined with low flow water fixtures and shower head adapters, tankless hot water systems, control the use of potable water and are energy saving appliances, using existing technology to reduce the use of energy in homes.

Tankless hot water heaters save water, space and energy. They can be used in commercial installations with limited warranties as well as in the residential applications. They can be placed inside or outside. Tankless hot water heaters can be designed to provide hot water for the whole house and located in a central equipment area, but they can also reduce extensive plumbing runs by locating them near clusters of fixtures. Designers, seeking to maximize efficiency through design will welcome this technology as an effective means to achieve sustainable design goals as well as complete their energy saving, hot showers.

 

Celeste Novak, AIA, LEED AP, is a principal at RizzoloBrown + Novak in Ann Arbor, Michigan and author of articles focusing on sustainable building materials and products.

 

The GE brand is easily identified for our distinguished heritage and our dedication to quality, forward-thinking products. And, for more than 125 years, GE has earned the trust of builders and homeowners around the world.  www.geappliances.com