Inputs
Example data table
| Home | Heater kW | Baseline hrs/day | Scheduled hrs/day | Peak/Off-peak | Estimated savings range |
|---|---|---|---|---|---|
| Apartment A | 3.5 | 3.2 | 2.0 | 0.20 / 0.13 | 6% to 18% monthly |
| House B | 4.5 | 4.0 | 2.5 | 0.22 / 0.14 | 10% to 25% monthly |
| Small office C | 6.0 | 5.5 | 3.5 | 0.28 / 0.18 | 8% to 20% monthly |
Formula used
- Energy (kWh/month) = Power (kW) × Hours/Day × Days/Month
- Blended rate = Peak Share × Peak Rate + (1 − Peak Share) × Off-peak Rate
- Baseline cost = Baseline kWh × Baseline blended rate
- Scheduled cost = (Scheduled kWh + Standby kWh) × Scheduled blended rate
- Standby kWh = Standby Loss (kW) × Standby Hours Off/Day × Days/Month
- Savings = Baseline cost − Scheduled cost
How to use this calculator
- Enter heater power from the rating label (kW).
- Estimate baseline runtime and scheduled runtime (hours/day).
- Enter your peak and off-peak electricity rates.
- Set peak share for both scenarios based on your routine.
- Add standby loss only if you want conservative estimates.
- Calculate, then export CSV or PDF for documentation.
Insights
Insights
Time-of-use price spread drives most savings
When peak pricing exceeds off-peak by 0.08 per kWh, shifting just 50% of heating off-peak can reduce blended cost noticeably. For a 4.5 kW heater running 4.0 hours daily over 30 days, baseline energy is 540 kWh. If 60% is peak, the blended rate becomes 0.188, producing about 101.52 monthly cost. If the spread narrows to 0.03, savings shrink quickly.
Runtime reduction compounds with scheduling
Schedules often cut runtime because the tank is not reheated continuously. Reducing runtime from 4.0 to 2.5 hours daily lowers heating energy from 540 to 337.5 kWh monthly. Even before any rate shifting, that change alone reduces consumption by 202.5 kWh, which is material for budgeting and demand planning. At 0.16 per kWh, that energy reduction is worth about 32.40 monthly.
Standby losses can narrow the headline savings
Turning a heater off for long blocks may introduce recoverable standby losses. Using a conservative 0.08 kW loss over 12 hours off adds 28.8 kWh per month. If scheduled peak share is 25%, the blended rate is 0.160. Scheduled total energy becomes 366.3 kWh, with a monthly cost near 58.61. Improving insulation can reduce standby power and protect savings.
Monthly results translate cleanly into annual planning
With the example inputs above, estimated monthly savings are about 42.91 and annualized savings about 514.92. Those values support payback estimates for timers, smart controls, or insulation upgrades. If equipment costs 40 to 70, the simple payback can fall below two months. Use a lower savings assumption when occupancy is irregular. Seasonal water temperature changes matter too.
Use the chart to validate assumptions quickly
The cost and energy bars highlight whether savings come from time shifting or runtime reduction. If energy barely changes but cost drops, your schedule is moving load to cheaper hours. If both bars drop, you are also reducing total heating demand. Review peak share inputs if results look unrealistic. Track one week of meter data to refine hours and shares.
FAQs
1) What if I only have a single electricity rate?
Set peak and off-peak rates to the same value, and keep peak shares equal. The calculator then estimates savings from runtime changes and standby assumptions only.
2) How do I estimate heater power in kW?
Check the label for watts and divide by 1000. For example, 4500 W equals 4.5 kW. If multiple elements exist, use the active element rating.
3) What does “peak share” mean?
It is the percentage of heating that occurs during your higher-priced time window. If most heating happens in evenings, peak share is usually higher than 50%.
4) Should I always include standby loss?
Include it when you want a conservative result or you expect long off periods. If your tank is well insulated, standby loss may be small and savings may be higher.
5) Why can scheduled energy be higher than baseline?
If standby loss is large or scheduled hours are not reduced, total energy can rise. Adjust standby inputs or schedule hours to reflect real operation.
6) Can this be used for gas water heaters?
This version is designed for electricity and time-based pricing. For gas, convert to equivalent energy and rates, but accuracy depends on burner efficiency and tariff structure.