Calculator inputs
Enter your annual HVAC costs and expected leakage reduction. Use the advanced options to estimate NPV over time.
Example data table
Sample scenarios to show typical output patterns.
| Scenario | Annual HVAC Cost | Leak Before | Leak After | Project Cost | Annual Savings | Payback |
|---|---|---|---|---|---|---|
| Typical attic ducts | $1,500 | 22% | 10% | $500 | $108 | 4.63 yrs |
| Higher leak reduction | $2,100 | 28% | 8% | $650 | $252 | 2.58 yrs |
| Conditioned duct run | $1,800 | 18% | 8% | $450 | $22 | 20.45 yrs |
Examples assume standard assumptions and may differ from your inputs.
Formula used
- Annual HVAC cost: Heating Cost + Cooling Cost
- Effective distribution loss: min(45%, Leakage% × 0.60 × LocationFactor)
- Estimated annual savings: Annual HVAC Cost × (Lossbefore − Lossafter)
- Net project cost: max(0, Project Cost − Rebate)
- Simple payback (years): Net Project Cost ÷ Annual Savings (only when savings > 0)
- NPV: −NetCost + Σt=1..N [ Savings×(1+Esc)t−1 ÷ (1+Disc)t ]
LocationFactor reflects how much leaked air is “lost” to unconditioned space. Ducts inside conditioned space typically yield smaller bill impacts.
How to use this calculator
- Enter your annual heating and cooling costs from utility bills.
- Set duct leakage before and expected leakage after sealing.
- Select duct location to adjust the impact of leakage.
- Add project cost and any rebates to estimate net investment.
- Use analysis years, discount rate, and escalation for long-term value.
- Click Calculate savings to view results above the form.
- Download CSV or PDF to save and share your estimate.
For best accuracy, use duct-leakage test results, and confirm sealing quality with post-work testing.
Leakage Benchmarks And Where Losses Happen
Testing often finds total duct leakage near 10%–30% of airflow. Ducts in attics or vented crawlspaces can leak conditioned air outdoors, raising loads and run time. This calculator applies location factors to reflect typical exposure: attic 1.00, garage 0.90, crawlspace 0.80, conditioned space 0.20. Lower factors mean the same leakage creates smaller billing impacts.
Bill Impact Model Used In This Calculator
Annual HVAC cost equals heating plus cooling. Effective distribution loss is estimated as min(45%, Leakage% × 0.60 × LocationFactor). The 0.60 coefficient reflects that some leakage returns to the home and some losses overlap with normal infiltration. Example: 20% leakage in an attic becomes 12% effective loss (20 × 0.60 × 1.00). Reducing leakage to 8% becomes 4.8%.
Savings Scenarios With Payback Ranges
A $1,500 annual HVAC spend and leakage improving from 22% to 10% estimates about $108 savings per year, matching the sample table. If net project cost is $500, simple payback is roughly 4.63 years. With a $2,100 bill and 28% to 8% leakage, savings rise to about $252 per year; a $650 net cost implies a 2.58‑year payback. A $100 rebate reduces a $600 job to $500 net, materially shortening payback without changing energy performance estimates.
Long‑Term Value Using NPV And Escalation
NPV converts future savings into today’s value using a discount rate and an escalation rate for energy prices. For planning, many users test 3% escalation and 6% discount. If annual savings start at $250, 10 years of escalated savings total about $2,865 nominal. Discounted to present, the value is lower, helping you compare fairly against net project cost.
Implementation Notes For Audits And Reporting
For credibility, record pre‑ and post‑sealing leakage tests, scope notes, and incentive documentation. Enter verified bill totals, then update “after” leakage using post‑work measurements. Exports capture inputs and results for client reports or internal finance review. Pair financial outputs with comfort indicators, reduced equipment cycling, and maintenance plans to present a complete investment case.
FAQs
1) What should I enter if I don’t know my leakage rate?
Use typical planning values: 15%–25% before sealing and 6%–12% after. Then rerun the estimate with test results from a duct leakage or blower-door assessment for better accuracy.
2) Why does duct location change the savings so much?
Leaks in attics, garages, or crawlspaces usually spill conditioned air outside the living area. Ducts inside conditioned space can “leak” back indoors, so the bill impact is smaller even if measured leakage is similar.
3) What discount rate should I use for NPV?
Use your best alternative return for similar risk, such as loan APR or a conservative investment rate. A higher discount rate lowers NPV and makes long-term savings less valuable in today’s money.
4) Can the calculator show negative savings?
Yes. If the “after” leakage exceeds the “before” value, or if ducts are mostly conditioned, the model may show minimal or negative savings. Treat that as a signal to verify inputs and confirm leakage measurements.
5) Does this include comfort benefits or system downsizing?
No. The estimate focuses on bill savings from reduced distribution losses. Comfort improvements, reduced hot/cold rooms, and potential downsizing may add value, but they require additional modeling and verification.
6) How do I use the CSV and PDF exports?
Export after calculating to preserve assumptions, inputs, and results for documentation. Share files with contractors, program administrators, or internal reviewers, and keep versions for before/after comparisons when you update leakage or rebates.