If the environmental impact of your energy choices is important to you, a single-tank system can offer impressive savings. Here’s the skinny on shrinking your household’s greenhouse gas emissions where water heating is concerned.
Of water-heating appliances, tank-style water heaters fueled with natural gas can create some of the greatest carbon dioxide emissions—a ton or more of CO2 per year. Replacing a gas-fired tank-style heater with a tankless gas water heater can cut these emissions by about 15%. Combining a solar preheating system with a tankless backup is a much bigger step in reducing your environmental footprint—at least four times greater (60%) in terms of energy and environmental savings.
Because sources of electricity vary, it’s more difficult to determine the amount of CO2 produced from the electricity used to heat water. Most of the electrical generation in the United States is from coal, which produces copious amounts of CO2. However, if you live in a region of the country where hydro is used to generate electricity (up to 40% of the electricity supply in some areas), your carbon footprint is proportionally reduced. Ask your local utility for its percentages. If they participate in “green” energy options, pony up to purchase clean, renewably generated electricity.
If you’re using electricity generated from a wind turbine or photovoltaic modules for water heating, you should have a clear CO2 conscience in regard to water heating. But whatever your source of energy, if you use solar thermal as your primary heat source, you’ll achieve 55% to 85% of your water heating with the energy of the sun.