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Example Data Table
This sample shows how typical setback choices can impact yearly costs.
| Annual HVAC Cost | Heating Share | Cooling Share | Degrees | Hours/Day | Days/Year | Est. Annual Savings |
|---|---|---|---|---|---|---|
| $1,800 | 55% | 25% | 6 | 8 | 240 | ~$118 |
| $2,400 | 60% | 30% | 8 | 10 | 260 | ~$240 |
| $1,200 | 50% | 20% | 4 | 6 | 200 | ~$45 |
Example savings assume 1% per degree per 8 hours and a 10% rebound penalty.
Formula Used
The calculator uses a practical rule-of-thumb model that converts your setback schedule into an estimated savings rate.
- Gross Savings Rate = Degrees × (Hours ÷ 8) × (PercentPerDegree8h ÷ 100) × (Days ÷ 365)
- Net Savings = (HeatingCost + CoolingCost) × GrossRate × (1 − ReboundPenalty)
This is an estimate. Real savings depend on insulation, equipment efficiency, weather, humidity, and comfort choices.
How to Use This Calculator
- Enter your annual heating and cooling cost total.
- Estimate what percent is heating and cooling.
- Set the degree change and daily setback hours.
- Choose how many days you follow the schedule.
- Adjust the savings factor and rebound penalty.
- Press Calculate to view savings above the form.
- Download CSV or PDF if you need records.
Why thermostat setbacks can cut costs
Heating and cooling often dominate household utility budgets. A setback lowers winter temperatures or raises summer setpoints for part of the day, shrinking the indoor–outdoor difference. With less difference, heat moves more slowly and HVAC equipment runs fewer hours. This calculator turns your annual HVAC spend into a baseline and applies an adjustable savings rate based on degree change, setback hours, and days followed.
How the calculator estimates gross savings
A planning guideline is about 1% savings per degree held for eight hours. The “Savings factor” lets you tune that assumption to match your building and climate. Example: a 4°F change for 8 hours across 200 days gives a gross rate near 4% × 200/365 ≈ 2.19% annually. On a $2,400 HVAC budget, gross savings are about $52.56.
Rebound, limits, and the season split
Some systems work harder when returning to comfort, especially with large swings or humidity. The rebound penalty reduces gross savings into a conservative net estimate. The heating/cooling split matters too. If 70% of your cost is heating, winter setbacks drive most of the savings. The summary table separates heating and cooling impacts for clearer budgeting.
Reading monthly savings and payback
Monthly savings equals net annual savings divided by twelve, helpful for household cash flow. If you’re buying a smart thermostat, enter the one-time cost to estimate payback. A $180 upgrade with $6.50 monthly savings pays back in roughly 27.7 months. After payback, the savings persist as lower bills, assuming similar prices and usage.
Using results to plan and track
Begin with a modest degree change and confirm comfort. Compare the “New annual HVAC cost” to your baseline to set a realistic target. Export CSV or PDF to document assumptions, then review after a billing cycle. If real-world savings differ, adjust the savings factor or rebound penalty. Combine consistent setbacks with basic weatherization for larger annual gains with minimal upfront effort.
FAQs
What does “setback” mean in this calculator?
A setback is a planned change to your thermostat for part of the day. In winter you lower the setpoint; in summer you raise it. The calculator estimates how that schedule can reduce annual HVAC run time and cost.
How should I choose the savings factor?
Start near 1.0 for an average home. Use a lower value for leaky homes or mild climates, and a higher value for efficient systems and consistent schedules. If you have bill history, adjust until estimates resemble observed seasonal changes.
What is the rebound penalty?
Rebound represents extra energy used when the system returns to the comfort setpoint. Large temperature swings, high humidity, and some heat pump behaviors can reduce savings. A 10% penalty is a cautious default when you’re unsure.
Why do heating and cooling savings appear separately?
Heating and cooling loads respond differently to setbacks and weather. Splitting the costs helps you see which season drives savings, and it supports better planning if your home mainly heats or mainly cools during the year.
Can I use this for a smart thermostat purchase decision?
Yes. Enter the device and installation cost as the upgrade cost. The payback estimate divides that cost by the monthly savings. It’s a planning figure; your actual payback depends on usage, energy prices, and comfort settings.
How accurate are the results?
They are directional estimates. Real savings vary with insulation, occupancy, equipment efficiency, humidity, and how often the schedule is overridden. Track one or two billing cycles, then refine the savings factor and rebound penalty to match reality.