Estimate the monthly and yearly electricity cost for an electric water heater using daily hot water use, temperature rise, price, and efficiency.
Advanced options
Table of contents
How to use our Electric Water Heater Cost Calculator
- Enter Hot water used in gallons per day, then enter Cold water temperature and Hot water setting in degrees F.
- Enter Electricity price as the full $ per kWh from your bill, including delivery charges if your bill separates them.
- Enter Current heater efficiency as UEF. Use the label value if you have it, or keep the sample value for a rough standard electric tank estimate.
- Open Advanced options if you want Days in monthly bill, Extra measured use, Compare with efficiency, or Extra upfront cost to compare.
- Click Calculate, then sanity-check the result: higher gallons, a bigger Temperature rise, or a higher Electricity price should raise the Estimated monthly cost.
Definitions
Hot water used: The estimated gallons of heated water used per day, not total cold and hot water combined.
Temperature rise: Hot water setting minus Cold water temperature, measured in degrees F.
Electricity price: The price you pay for each kWh of electricity. A kWh is a unit of electric energy on your utility bill.
UEF: Uniform Energy Factor. It rates water heater efficiency. Higher UEF means less electricity for the same hot water use.
Extra measured use: Extra kWh per day that you measured separately, such as standby use from an energy monitor.
Simple payback time: Extra upfront cost to compare divided by positive yearly savings. It is a rough break-even time in years.
Common mistakes and quick fixes
Mistake: Entering total household water use in Hot water used instead of hot water only.
Fix: Use only the hot water share for showers, laundry, dishes, and hand washing in Hot water used.
Mistake: Setting Hot water setting equal to or below Cold water temperature.
Fix: Make Hot water setting higher than Cold water temperature so Temperature rise is positive.
Mistake: Typing a monthly bill total into Electricity price.
Fix: Enter the rate in Electricity price, such as 0.17 for 17 cents per kWh.
Mistake: Leaving Current heater efficiency blank or entering 0.
Fix: Enter a Current heater efficiency greater than 0, such as 0.93 for a standard electric tank estimate.
Mistake: Adding standby use twice by increasing both Extra measured use and lowering Current heater efficiency.
Fix: Use Extra measured use only when you have measured extra kWh per day from a monitor.
Mistake: Reading Yearly savings with comparison UEF as always positive.
Fix: If Yearly savings with comparison UEF is negative, the comparison setup costs more for the entered use and price.
Limitations & Key Assumptions / Boundary Conditions
- The estimate is for electric operating cost only. It does not include installation, maintenance, plumbing changes, rebates, taxes, or financing.
- The water-use estimate is only as good as Hot water used. Actual gallons can change with shower length, fixture flow, laundry settings, guests, and leaks.
- Cold water temperature can change by season and location. A colder inlet temperature raises Temperature rise and cost.
- UEF is used as a simple efficiency factor. Real performance can differ with tank size, draw pattern, room temperature, controls, and heat pump operating mode.
- Extra measured use is added only to the current heater estimate. The comparison estimate uses the same hot water load but does not add that extra kWh.
- Simple payback time is shown only when Extra upfront cost to compare is entered and Yearly savings with comparison UEF is positive.
Methodology
Calculation steps
The calculator first finds the Temperature rise, then estimates the useful heat needed to warm the entered gallons of water each day. It converts that heat to kWh, adjusts for Current heater efficiency, adds any Extra measured use, and multiplies by Electricity price.
Temperature rise = Hot water setting - Cold water temperature
Useful Btu per day = Hot water used * 8.34 * Temperature rise
Electricity used per day = Useful Btu per day / 3412 / Current heater efficiency + Extra measured use
Estimated monthly cost = Electricity used per day * Electricity price * Days in monthly bill
Estimated yearly cost = Electricity used per day * Electricity price * 365
For the comparison, the same gallons, temperatures, and electricity price are used, but Current heater efficiency is replaced by Compare with efficiency. Yearly savings with comparison UEF is signed, so a negative value means the comparison costs more.
Comparison kWh per day = Useful Btu per day / 3412 / Compare with efficiency
Yearly savings with comparison UEF = Estimated yearly cost - (Comparison kWh per day * Electricity price * 365)
Simple payback time = Extra upfront cost to compare / Yearly savings with comparison UEF
Mini-example
With 50 gallons per day, 55 F cold water, a 120 F hot setting, $0.17 per kWh, and a 0.93 UEF heater, the Temperature rise is 65 F. The useful heat is 50 * 8.34 * 65 = 27,105 Btu per day. Daily electricity is 27,105 / 3412 / 0.93 = about 8.54 kWh per day. For a 30.44-day bill, the Estimated monthly cost is 8.54 * $0.17 * 30.44 = about $44.20.