Estimate yearly electricity savings, avoided standby energy, and timer payback from your electric tank water heater schedule and rates.
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Table of contents
How to use our Water Heater Timer Savings Calculator
- Enter your Water heater energy used each day and Standby energy used each day. Standby energy must not be higher than total daily energy.
- Set Timer turns off at and Timer turns back on at for the daily period when you plan to keep the tank off.
- Enter your utility's Peak electricity rate and Off-peak electricity rate.
- Open Advanced options to set the peak period and add Timer purchase price and Timer setup cost if you want a payback estimate.
- Check that the reported off-window length and estimated standby energy avoided each day match your schedule. Then compare estimated annual electricity bill savings with the timer's total one-time cost.
Definitions
Standby energy: Electricity used to replace heat lost from stored tank water while no hot water is being drawn. Electric storage water heaters have standby and cycling losses. [1]
Peak period: The daily hours your utility charges at the higher electricity price.
Off-peak rate: The electricity price used outside the peak period in this estimate.
Timer off window: The time from Timer turns off at until Timer turns back on at, including a window that crosses midnight.
Payback time: The one-time timer and setup cost divided by estimated yearly bill savings.
Common mistakes and quick fixes
Mistake: Entering total water-heating energy as Standby energy used each day.
Fix: Enter only the energy used to keep stored water hot when no hot water is being used. It must be no more than Water heater energy used each day.
Mistake: Setting Timer turns off at and Timer turns back on at to the same time.
Fix: Choose different times so the daily off period is clear. Use an overnight end time if needed.
Mistake: Using one blended utility price for both Peak electricity rate and Off-peak electricity rate when your plan has time-based pricing.
Fix: Copy the two rates from your electricity plan and set Peak period starts at and Peak period ends at to the matching daily hours.
Mistake: Reading Estimated annual electricity bill savings as savings from all water-heater use.
Fix: This estimate prices only standby energy avoided while the timer is off. It does not reduce hot-water energy based on fewer showers or loads of laundry.
Mistake: Forgetting electrician labor in Timer setup cost.
Fix: Include all one-time setup charges with Timer purchase price before using Estimated timer payback time to make a buying decision.
Limitations & Key Assumptions / Boundary Conditions
- This is for an electric tank water heater. It does not model gas, heat-pump, tankless, or solar water heaters.
- The estimate assumes standby energy is spread evenly across all 24 hours. Real tank heat loss can change with room temperature, tank temperature, insulation, and hot-water draws.
- It counts only standby energy avoided while the timer is off. It does not model extra reheating after power returns, a timer's own electricity use, or changes in hot-water demand.
- Peak and off-peak periods are treated as one repeating daily window each. Plans with seasonal rates, weekends, holidays, demand charges, or more than two price periods need a separate calculation.
- A timer can leave less hot water available and may not fit every household schedule. Follow the water heater and timer instructions, local electrical rules, and any safety requirements before installation.
- Payback is omitted when one-time cost or estimated annual bill savings is $0.
Methodology
Calculation method
The calculator compares an always-available electric tank with a timer that turns the tank off for part of each day. It treats only the entered standby energy as avoidable during that off window.
off_hours = (off_end_hour - off_start_hour + 24) mod 24
Equal start and end times are rejected because they could mean either no off time or a full-day off period. Timer and peak periods can cross midnight. The calculator splits overnight periods at midnight to find their overlap.
daily_energy_avoided_kwh = daily_standby_kwh * off_hours / 24
daily_bill_savings = daily_standby_kwh * (peak_overlap_hours / 24) * peak_rate + daily_standby_kwh * ((off_hours - peak_overlap_hours) / 24) * offpeak_rate
annual_energy_avoided_kwh = 365 * daily_energy_avoided_kwh
annual_energy_before_kwh = 365 * daily_energy_kwh
annual_energy_after_kwh = annual_energy_before_kwh - annual_energy_avoided_kwh
annual_bill_savings = 365 * daily_bill_savings
timer_payback_years = (timer_cost + installation_cost) / annual_bill_savings
Mini-example
Suppose standby energy is 3 kWh per day and the timer is off from 9:00 AM to 5:
00 PM, or 8 hours. Avoided standby energy is 3 * 8 / 24 = 1 kWh per day, or 365 kWh per year. If one of those hours overlaps a $0.30 per kWh peak period and seven hours use a $0.10 per kWh off-peak rate, yearly bill savings are $45.625. With a $30 timer and $70 setup cost, estimated payback is about 2.19 years.
The yearly comparison uses 365 days and 24 hours per day. A $0 one-time cost has no payback time because there is no cost to recover; $0 estimated annual bill savings also prevents a payback calculation.