Water Heating Sources
background
On average, 13% to 26% (17% overall) of energy in a US household is consumed heating water[1].
What energy sources cost the least to heat water and generate the least amount of green-house-gases (GHG)?
Table comparing solar water-heating with heating water using other fuel types and energy sources
| fuel type or energy source | cost per kWh when heating water | average GHG output (pounds CO2e per year per US household) | references |
|---|---|---|---|
| biomass | $0.04 to $0.06 | >5,000 | see IEA Bioenergy Task 38 for helping mitigate co2 emissions, price from bioenergy.ornl.gov |
| electricity from utility | $0.10 to $0.11 | 3,762 | GHG conversion from Climate Trust, price from EIA |
| fuel oil | $0.16 | 5,205 | GHG conversion from Climate Trust, price from EIA and water heating efficiencies derived from EIA Water Heating Consumption Report |
| heatpump | $0.32 to $0.64 | <3,500 | price from ACEEE Report: Residential Heat Pump Water Heaters (pdf) |
| liquid propane gas | $0.09 | 2,318 | GHG conversion from Climate Trust, price from EIA and water heating efficiencies derived from EIA Water Heating Consumption Report |
| natural gas from utility | $0.10 | 2,532 | GHG conversion from Climate Trust, price from EIA and water heating conversion efficiencies derived from EIA Water Heating Consumption Report |
| photovoltaics | $0.23 to $0.32 | 0 | price from EERE |
| solar thermal | $0.05 to $0.10 | <1 | price from EERE |
| wind | $0.05 to $0.30 | 0 | price from EERE |
To help put GHG emissions in perspective, the average passenger vehicle in the US generates 11,374pounds CO2e per year[3].
Fuel types are converted to kWh for comparison purposes using this info: 1. fuel consumption data from EIA: Water Heating Consumption Report that summarizes averages for currently installed water heating devices, 2. electric conversion to heat energy is 100% efficient, 3. the assumption that average household hot water use is about the same for electric energy consumption as other utility fuels, 4. Fuel specific pricing references which are listed in the table.
A special note about instant water heaters, since they are sometimes offered as a water-heating solution. Instant water heaters use various utility sources to only heat water that gets used. Instant water heaters are indicated in places where little hot water is used and more energy is spent keeping water heated and ready for use than in actually heating water that is used --such as in a one person household where the person is rarely home. Regardless, know that electric instant water heaters can carry an extra burden on the energy grid instead of reducing overall energy footprint. Read more in PureEnergySystem's article Tankless Water Heaters Stress Electric Grid.
conclusion
Conventional household heating of water is a significant contributor to green-house-gases (GHG)[2] and a household's water heating costs.
Solar water-heating systems significantly reduce the amount of conventional power consumed in the process of heating water.
Reducing conventional power used to heat water also reduces GHG and heating costs. The more water is heated by the sun, the less money is spent using conventional energy to heat water (and less GHG contributes to global warming).
Read about solar water heating systems, designs, how they work and which system is best for each location.
- 1 - according to the US Energy Information Administration (EIA) data. The EIA also states that there are 2.6 people per household on average.
- 2 - extrapolated from EIA data with GHG and CO2e equivalents from The Climate Trust.
- 3 - EPA Office of Transportation and Air Quality calculates Total Annual Pollution Emitted and Fuel Consumed based on an average annual passenger car mileage of 12,500 miles at 21.5mph, as reported in 19th ed. of "Transportation Energy Data Book," prepared for the U.S. Department of Energy. The CO2e conversion of 19.564 pounds CO2e per gallon is from Climate Trust.