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Quick guidance
- Measure heating and cooling from your latest bills.
- Choose a reduction percent based on draft severity.
- Include tape, foam, door sweeps, and labor costs.
- Compare simple and discounted payback for planning.
- Use exports to share results with your household.
Example data table
| Scenario | Heating | Cooling | Reduction | Cost | Lifespan | Year-1 Savings | Simple Payback |
|---|---|---|---|---|---|---|---|
| Small apartment | $450 | $350 | 10% | $90 | 5 | $80 | 1 year 2 months |
| Average home | $900 | $600 | 12% | $180 | 7 | $180 | 1 year |
| Drafty older home | $1,600 | $900 | 18% | $350 | 8 | $450 | 9 months |
Formula used
Annual energy cost = Heating cost + Cooling cost.
Year-1 savings = Annual energy cost × (Reduction % ÷ 100).
Year t savings = Year-1 savings × (1 + Escalation %)^(t−1).
Present value (PV) savings = Σ[ Year t savings ÷ (1 + Discount %)^t ].
Simple payback = Project cost ÷ Year-1 savings.
Net savings = Lifetime savings − Project cost (nominal or PV).
How to use this calculator
- Find your annual heating and cooling spending from recent bills.
- Estimate a reduction percent based on how drafty the home feels.
- Enter your total project cost, including materials and labor.
- Set lifespan to how long the sealing remains effective.
- Use advanced assumptions to model price growth and discounting.
- Press Calculate to view savings above the form, then export if needed.
Insights
Why air sealing changes the bill
Weatherstripping targets air exchange around doors, windows, and attic hatches. When warm air leaks out in winter, heating systems run longer to maintain the thermostat setpoint. In summer, humid air enters and increases cooling and dehumidification loads. The calculator translates those effects into money by applying an estimated percentage reduction to your annual heating and cooling spend.
Turning utility costs into savings
Year‑1 savings equals annual energy cost multiplied by the reduction percentage. If your heating cost is 900 and cooling cost is 600, the annual total is 1,500. A 12% reduction produces 180 in first‑year savings, or about 15 per month. This is a typical budget-oriented estimate that is easy to compare against the project cost and the expected lifespan of the materials.
Payback and return metrics
Simple payback divides the project cost by year‑1 savings, showing how quickly cash outflows can be recovered. ROI uses net lifetime savings divided by cost, expressed as a percentage. These measures are most useful when you are deciding between a quick DIY approach, a higher-quality installation, or bundling sealing with other efficiency upgrades.
Price growth and present value
Energy prices rarely stay flat, so the model can apply an annual escalation rate to future savings. It also discounts those future savings back to today using a discount rate, producing present value totals and a discounted payback estimate. When escalation is higher than the discount rate, future savings become more valuable relative to today’s cost; when discounting dominates, near-term savings matter more.
Using results for better decisions
Treat the reduction percentage as a range rather than a single truth. Run a conservative case at 5% and an optimistic case at 20% to bracket outcomes. If payback is acceptable in both scenarios, the project is robust. If results vary widely, improve your estimate by checking for visible gaps, using smoke or incense near frames, and tracking bills for another season.
FAQs
What reduction percentage should I use?
Start with 5% to 10% for newer homes and 12% to 20% for drafty homes. If you are unsure, run low and high cases to see a realistic range of savings.
Does this include insulation upgrades?
No. It estimates savings from air sealing only. If you add insulation, replace windows, or upgrade HVAC, calculate those projects separately and then compare combined costs and benefits.
Why are there two payback numbers?
Simple payback uses first-year savings only. Discounted payback considers price escalation and discounts future savings to today, which can change the timeline for long-lived projects.
What should I include in project cost?
Include weatherstripping materials, door sweeps, adhesive, tools, and any labor. If you plan maintenance or replacement during the lifespan, add a reasonable allowance to avoid underestimating cost.
How accurate are the results?
Accuracy depends on your energy costs and the true leak reduction. Use your latest bills, choose a conservative reduction, and verify drafts after installation. Savings can vary by climate and occupant behavior.
Can I use this for apartments or small spaces?
Yes. Enter your own heating and cooling costs, even if they are smaller. Smaller bills mean smaller savings, but low project costs can still produce a fast payback.