# CALCULATIONS FOR ENERGY SAVINGS FROM REDUCED WATER CONSUMPTION

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```					CALCULATIONS FOR ENERGY SAVINGS FROM REDUCED WATER
CONSUMPTION
(Based on savings from installing low-flow showerheads, faucet aerators, etc.)

   Assumptions and Constants –
o Calculate the total amount of water saved per year by installing water-saving
devices on fixtures using hot water (showers, lavatories, dishwashers, etc.)
o Calculate how much of this saving is actually hot water (assume 50% unless there
is a reason to assume otherwise)
o One therm = 100,000 Btu
o Cost of natural gas = \$1.12/therm
o Water weighs = 8.34 lb/gal
o Cost of electricity = \$0.11/kWh
o To increase the temperature of 1 lb of water 1° F requires 1 Btu
o There are 3412 BTU per kWh
o Assume a temperature rise (Δt) of 80° (temperature of hot water from water heater
minus temperature of incoming cold water)

   Procedure
o Determine the number of gallons of hot water saved by converting to low-flow
showerheads, faucet aerators, or other water-saving device, assuming that 50% of
water saved is hot water.
o Convert the amount of hot water saved to pounds
Gallons of hot water saved × 8.34 lb/gal = pounds of hot water saved
o Calculate the energy required to heat this amount of water
Pounds of hot water saved × 80º temperature rise = total Btu
o Convert the total energy (Btu) to therms or kWh
Total Btu ÷ 100,000 = number of therms saved
Total Btu ÷ 3412 = number of kWh saved
o Use a Heating Source Efficiency Multiplier
Natural gas heating at 80% efficiency. Multiply total energy by 1.25
o Calculate the dollar savings
For gas water heaters – Total number of therms × \$1.50 = dollar savings/yr
For electric heaters – Total number of kWh × \$0.11 = dollar savings/year

Waste Reduction Partners: Assessor Reference Materials, March 2006
Rev. 4/2008

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