Duct Leakage Savings Calculator

Enter Your Details

Annual heating cost ($/year)

Use your last 12 months billing total if possible.

Annual cooling cost ($/year)

Include central AC or heat pump cooling costs.

Duct location

Outside-envelope ducts tend to waste more energy.

Leakage before sealing (%)

Common ranges: 10–30% for many homes.

Leakage after sealing (%)

A realistic target might be 5–12%.

Sealing cost ($)

Include testing, materials, and labor.

Rebate / incentive ($)

Enter 0 if none.

Analysis period (years)

Used for NPV and IRR estimates.

Discount rate (% per year)

A typical range might be 3–10%.

Energy price escalation (% per year)

Use 0–3% if unsure.

Reset

Example Data Table

Sample inputs and outputs to illustrate typical ranges.

Heating cost	Cooling cost	Location	Leakage (before → after)	Sealing cost	Rebate	Estimated annual savings	Payback
$900	$600	Attic	20% → 8%	$800	$150	$216	3.01 years
$1,200	$800	Crawlspace	25% → 10%	$1,000	$200	$300	2.67 years
$700	$500	Conditioned space	15% → 7%	$600	$0	$48	12.50 years

Note: outputs vary by duct location, leakage reduction, and baseline HVAC spending.

Formula Used

Total annual HVAC cost = heating cost + cooling cost
Effective loss fraction = (leakage % ÷ 100) × location multiplier, capped at 60%
Estimated leakage cost = total HVAC cost × effective loss fraction
Annual savings = leakage cost (before) − leakage cost (after)
Net upfront cost = sealing cost − rebate (minimum 0)
Simple payback = net upfront cost ÷ annual savings
NPV = −net upfront + Σ [ savings × (1+escalation)^(t−1) ÷ (1+discount)^t ]

This is a cost-based estimate designed for planning. Field testing (blower door/duct blaster) improves accuracy.

How to Use This Calculator

Enter your annual heating and cooling costs from utility bills.
Select where your ducts run (attic, crawlspace, basement, etc.).
Estimate current leakage and a reasonable post-sealing target.
Add your sealing quote and any available rebates or incentives.
Click Calculate Savings to view savings, payback, and NPV.
Download CSV/PDF to share results with contractors or homeowners.

Professional Notes

Where duct leakage costs hide

Heating and cooling bills already include losses you never feel. Leaky supply runs dump conditioned air into attics or crawlspaces, while return leaks pull dusty, hot, or humid air into the system. This calculator translates leakage percentages into an effective loss fraction using a location multiplier, then applies it to your annual HVAC spending for a quick cost estimate.

Inputs that drive savings accuracy

Start with your last twelve months of heating and cooling totals. If you have a duct test, use the measured leakage; otherwise, many homes fall near 10–30% before sealing. The duct location matters: ducts outside the building envelope typically waste more because the temperature difference is larger. Rebates reduce upfront cost and shorten simple payback.

Interpreting the results dashboard

The results block shows annual leakage cost before and after sealing, estimated annual savings, net upfront cost, payback, ROI, NPV, and an IRR estimate. Payback explains how quickly savings recover the net investment, while NPV discounts future savings to today’s dollars. A positive NPV indicates the project beats your chosen discount rate over the selected analysis years.

Using the graph for decisions

The Plotly chart compares “before” and “after” leakage costs as bars and visualizes discounted cumulative savings over time as a line. If the line crosses your net upfront cost early, the upgrade tends to be financially compelling. A flatter line can signal limited leakage reduction, ducts already inside conditioned space, or low baseline HVAC spending.

Practical next steps after calculating

Use the CSV or PDF export when requesting contractor bids so assumptions stay consistent. Ask for diagnostic testing, sealing of connections and boots, and verification after work. Pair duct sealing with air filter upgrades and balanced airflow to improve comfort. Re-run scenarios to compare different leakage targets and incentive levels before committing funds. For large homes, consider zoning and insulating exposed runs, then track bills for two seasons to validate real savings and adjust assumptions carefully afterward overall.

FAQs

Q1: What leakage percentage should I use if I have no test?
A: Many homes fall around 10–30% before sealing. Start with 20% before and 10% after, then refine using contractor testing or a duct blaster result.

Q2: Why does duct location change the savings so much?
A: Ducts in attics, crawlspaces, or garages lose more energy because surrounding temperatures are farther from indoor conditions, so the same leakage percentage creates larger effective losses.

Q3: Does this include comfort and air quality benefits?
A: The outputs focus on energy costs and financial metrics. Comfort improvements, reduced drafts, and fewer pollutants are real benefits, but they are not priced into the savings total.

Q4: What does NPV tell me that payback does not?
A: Payback shows time to recover cost. NPV accounts for discounting and energy escalation across years, helping compare sealing to other upgrades using consistent financial assumptions.

Q5: Can sealing ever have low savings?
A: Yes. If ducts are inside conditioned space, leakage reduction is small, or HVAC spending is already low, savings can be modest and payback may be long.

Q6: How should I verify results after work is done?
A: Ask for post-sealing testing, check airflow balance, and compare utility bills across similar weather periods. Update the calculator using measured leakage values for validation.