The Daily Water Heating Energy based on the DOE test procedure for hot water heaters assumes an incoming water temperature of 58☏, hot water temperature of 135☏, and total hot water production of 64.3 gallons per day, which is the average usage for a household of three people. The definition of Btu is energy required to raise one pound (lbs) of water by one degree Fahrenheit (F).ĭaily Water Heating Energy= (gallons of hot water per day)*(8.35 lbls/gallon)*(1 btu/lbs/F)*(Hot water temperature- Cold water temperature). The fuel used is related to the amount of water used and the temperature. For electric heaters the UEF is taken to be 1.0 since all the electricity goes into the water.ĭaily Water Heating Energy = (Summer months fuel use)*EF*0.6/(number of days in summer months) Household gas water heaters are required to have a UEF of at least 0.64. UEF is determined by the Department of Energy’s test method outlined in 10 CFR Part 430, Subpart B, Appendix E. The higher the UEF value is, the more efficient the water heater. If you have gas for cooking and clothes dryer, you might want to take about 60% of that summer total as the energy used to heat water.Ī conventional water heater's energy efficiency is the Uniform Energy Factor (UEF) which is the amount of hot water produced per unit of fuel consumed in a standard test. Look through your utility bills and see how much fuel you use in summer months, when gas is not used for space heating. WITH A GAS AUXILIARY TANK SYSTEM: Daily Water Heating Energyįuels such as natural gas are often sold in units of “therms.” One (1) therm equals 100,000 British thermal units (Btus). The auxiliary tank fuel type (gas or electric) and costs (your local utility can provide current rates).įirst calculate the amount of energy needed to heat water based on fuel use or gallons of hot water needed.To estimate the annual operating cost of a solar water heating system, you need the following: This will help you determine the energy savings and payback period of investing in a more energy-efficient system, which will probably have a higher purchase price.īefore you can choose and compare the costs of various systems, you need to know the system size required for your home. When selecting a solar water heater, it's also important to consider size and overall cost.īefore purchasing a solar water heating system, estimate the annual operating costs and compare several systems. This certification also lists how much heat (kWh or Btu) the system will deliver per day under different conditions of sunlight and temperature.ĭon't choose a solar water heating system based solely on its energy efficiency. Typical solar fraction values are 0.5–0.75.įor certified solar hot water systems the Solar Energy Factor and Solar Fraction are listed by the Solar Rating and Certification Corporation at. The higher the solar fraction, the greater the solar contribution to water heating, which reduces the energy required by the backup water heater. The solar fraction is the portion of the total conventional hot water heating load (delivered energy and tank standby losses). Systems with solar energy factors of 2 or 3 are the most common.Īnother solar water heater performance metric is the solar fraction. Solar energy factors range from 1.0 to 11. The higher the number, the more energy efficient. The solar energy factor is defined as the energy delivered by the system divided by the electrical or gas energy put into the system. Use the solar energy factor (SEF) and solar fraction (SF) to determine a solar water heater's energy efficiency. On a monthly basis, you're saving more than you're paying. So if your fuel savings are more than $15 per month, the solar investment is profitable immediately. The federal income tax deduction for mortgage interest attributable to the solar system reduces that by about $3–$5 per month. Including the price of a solar water heater in a new 30-year mortgage usually amounts to between $13 and $20 per month. If you're building a new home or refinancing, the economics are even more attractive. Also, because the sun is free, you're protected from future fuel shortages and price hikes. RADIANT FLOOR HEATING COST CALCULATOR INSTALLOn average, if you install a solar water heater, your water heating bills should drop 50%–80%.
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