How the Calculator Works
Daily Energy (kWh) = [(Runtime Hrs × Temp Delta) + (Setback Hrs × Setback Delta)] × 0.08 ÷ (Efficiency ÷ 100)Effective Delta-Hours: (Runtime Hours × Temperature Delta) + (Setback Hours × Setback Delta) — total daily heating/cooling load expressed in degree-hours.
Equivalent Full-Load Hours: Effective Delta-Hours ÷ Temperature Delta — the runtime needed at full delta to match the same total load.
Daily Cost: Daily Energy × Energy Rate.
Setback Savings: energy saved, at your Energy Rate, versus running at the full Temperature Delta for the entire combined schedule (Runtime Hours + Setback Hours) instead of using the Setback Delta.
0.08: baseline system load factor in kWh per °F of delta per hour of runtime at 100% efficiency.
Worked Example
- A 12°F delta at 85% efficiency for 6 runtime hours plus a 4°F setback for 8 hours totals about 9.79 kWh/day (about $1.76 at $0.18/kWh).
- That schedule is equivalent to about 8.7 hours of full-load runtime per day.
- Using the setback schedule saves roughly $1.08/day versus running at the full delta the entire time.
How to Interpret Your Results
| Equivalent Full-Load Hours | Typical Meaning | Recommended Action |
|---|---|---|
| Under 4 hrs/day | Low HVAC load. | Efficient schedule; minimal changes needed. |
| 4–8 hrs/day | Moderate HVAC load. | Balanced setup; fine-tune setback timing. |
| 8–12 hrs/day | High HVAC load. | Consider a deeper or longer setback. |
| Over 12 hrs/day | Extreme HVAC load. | Reassess insulation, delta, or equipment sizing. |
Frequently Asked Questions
How reliable are these environmental estimates?
These calculations use peer-reviewed emission factors, energy conversion constants, and environmental science formulas. They're accurate for ballpark estimation and comparison purposes. Real-world values vary based on local utility mix, climate, building materials, and individual habits. Use results to understand relative impact and identify the biggest opportunities for improvement.
What units does this calculator use?
Energy is expressed in kilowatt-hours (kWh) or British thermal units (BTU) depending on context. Emissions are typically in kilograms or pounds of CO2-equivalent (CO2e), which accounts for different greenhouse gases weighted by their warming potential. Check the labels on each result — mixing energy and emissions units is a common source of confusion.
How can I reduce my impact most effectively?
Focus on your largest consumption categories first — heating/cooling, transportation, and food typically account for 70-80% of a household's carbon footprint. Small improvements to high-volume activities outweigh large improvements to low-volume ones. Use the calculator to compare scenarios (e.g., LED vs. incandescent) to find the highest-leverage changes.
Are these calculations valid for my region?
Some inputs — especially electricity emissions factors — vary significantly by region based on your local grid's energy mix. A kWh of electricity in a coal-heavy grid emits 3-4× more CO2 than one from a renewable-heavy grid. If precision matters, find your regional emissions factor from your utility or the EPA's eGRID database and use it as a custom input.
Common Tip Percentages
| Service | Typical Tip Range | Notes |
|---|---|---|
| Restaurant (sit-down) | 15–20% | 20%+ for exceptional service |
| Food delivery | 10–20% | Consider extra for long distances |
| Taxi / rideshare | 10–20% | More for assistance with luggage |
| Hotel housekeeping | $2–5/night | Leave daily, not just at checkout |
| Barber / hair salon | 15–20% | On pre-discount total |
| Pizza delivery | 10–15% or $3–5 minimum | Higher in bad weather |
General Household Budget Ratios (50/30/20 Rule)
| Category | % of Net Income | Examples |
|---|---|---|
| Needs | 50% | Rent, groceries, utilities, insurance |
| Wants | 30% | Dining out, entertainment, hobbies |
| Savings / Debt | 20% | Emergency fund, retirement, extra payments |
Common Measurement Conversions for Everyday Use
| Quantity | US / Imperial | Metric Equivalent |
|---|---|---|
| 1 cup | 8 fl oz | 237 mL |
| 1 pint | 16 fl oz | 473 mL |
| 1 quart | 32 fl oz | 946 mL |
| 1 gallon | 128 fl oz | 3.785 L |
| 1 lb | 16 oz | 453.6 g |
| 1 ft | 12 in | 30.48 cm |