How much can insulation and air sealing save?
Quick Answer
Use heating and cooling spending when possible. The ENERGY STAR U.S. benchmark is an average 15% of heating and cooling costs, or an average 11% of total energy costs, for a specific cost-effective air-sealing and insulation package—not two percentages that can be applied to the same bill.
Build your estimate
Guided mode estimates a range from your home and project choices. Switch to audit results only when you have measure-specific reduction percentages.
Results
Complete the five short steps, then calculate.
Worked example: attic insulation plus air sealing
A mixed-climate 1,800 ft² home spends $1,800 per year on heating and cooling. An audit estimates 6% savings from attic insulation and 7% from whole-home air sealing. Installed costs are $2,400 and $900; a verified $500 rebate is assigned to insulation.
Combined reduction = [1 − (1 − 0.06) × (1 − 0.07)] × (1 − 0.10 overlap) = 11.3%
Annual savings = $1,800 × 11.3% = $204
Net cost = ($2,400 + $900) − $500 = $2,800
Simple payback = $2,800 ÷ $204 = 13.7 years
The arithmetic uses heating and cooling spending because weatherization does not normally reduce appliance loads, water heating, taxes, or fixed utility charges. Comfort and resilience benefits are also omitted.
How the estimate works
Guided mode assigns a conservative, typical, and optimistic load-reduction range to each selected project, then adjusts it for climate severity, home age and condition, HVAC efficiency, attic condition, and—when entered—insulation R-value improvement and affected area. The ranges are planning heuristics calibrated around the ENERGY STAR whole-package benchmark, not simulations of the building.
Annual HVAC cost = bill × (12 when monthly) × (HVAC share when using a total bill)
Combined savings = [1 − (1 − project 1) × (1 − project 2) × …] × (1 − overlap)
Example: 7%, 5%, and 2% projects with 10% overlap = [1 − 0.93 × 0.95 × 0.98] × 0.90 = 12.1%
Annual savings = annual HVAC cost × combined savings
Simple payback = net project cost ÷ first-year net savings
NPV = −net cost + Σ[(year-one savings × (1 + escalation)^(year−1) − maintenance) ÷ (1 + discount)^year]
Planning limit: tightening a home can affect ventilation, moisture, radon, fireplaces, combustion appliances, and indoor air quality. Use qualified help for blower-door testing, combustion-safety checks, and code-required ventilation. Savings can also be reduced by installation defects, behavior changes, rebound effects, or weather that differs from the assumed climate.
Assumptions, sources, and trust signals
Method authored by the Starlight Tools editorial team and technically reviewed against the official sources below on July 18, 2026. No contractor, utility, government agency, or product manufacturer reviewed or endorsed this calculator.
| Default or benchmark | Value used | Source and scope | Publication / verification | Applicable conditions |
|---|---|---|---|---|
| Seal + insulate benchmark | 15% HVAC costs; 11% total energy costs | ENERGY STAR methodology; modeled typical existing U.S. homes | Source current; verified July 18, 2026 | Cost-effective air sealing plus attic, floor/crawl-space, and accessible rim-joist insulation; national weighted average |
| Guided project ranges | Project-specific conservative / typical / optimistic percentages shown in results | Starlight Tools planning model calibrated to the ENERGY STAR benchmark and DOE insulation / air-sealing guidance; not official project savings claims | Model version July 18, 2026 | Heating/cooling cost basis; adjusted by entered home characteristics; audit mode supersedes these defaults |
| Loaded home / project example | 1,800 ft², R-19 to R-49 attic, $2,400 attic + $900 sealing, $500 incentive | Starlight Tools reproducible worked example; not a market-cost or code recommendation | Model version July 18, 2026 | Replace with measured area, local code/audit R-values, contractor quotes, and verified award amounts |
| U.S. electricity price | $0.173/kWh | U.S. EIA Electric Power Monthly; U.S. residential annual average for 2025 | Preliminary 2025 data; verified July 18, 2026 | National average; excludes local tariff structure and fixed-charge effects |
| U.S. natural gas price | $1.53/therm | U.S. EIA residential gas price; 2025 average converted approximately from $15.34 per thousand ft³ | Released June 30, 2026; verified July 18, 2026 | National approximation; actual heat content and utility rates vary |
| U.S. oil / propane prices | $3.70 / $2.67 per gallon | U.S. EIA Heating Oil and Propane Update; rounded 2025–26 heating-season planning inputs | Season ended March 30, 2026; verified July 18, 2026 | Seasonal national values; delivery, taxes, tank terms, and region can materially change price |
| U.S. grid CO₂ | 0.348 kg/kWh | EPA eGRID 2023; U.S. total output rate of 767.25 lb/MWh | Data year 2023; page updated September 29, 2025; verified July 18, 2026 | Generation output average; not a marginal avoided-emissions forecast and excludes line losses |
| Gas / oil / propane CO₂ | 5.30 kg/therm; 10.19 / 5.75 kg/gallon | EPA combustion factors; U.S. fuel combustion | Source reviewed July 18, 2026 | Direct combustion planning factors; upstream emissions excluded |
| Financial defaults | 15 years; 2% escalation; 3% discount; 10% overlap | Starlight Tools transparent planning assumptions, not forecasts | Model version July 18, 2026 | Editable; escalation is nominal and discounting produces present-value dollars |
| Great Britain / EU rate presets | Rounded values loaded when selected | Starlight Tools illustrative mid-2026 planning inputs, explicitly not official averages | Model version July 18, 2026 | Use only as placeholders; replace with supplier tariffs, official national fuel conversions, and national grid factors |
Replace estimates with better evidence
Use a utility bill analysis for the cost basis, a blower-door test for leakage, an audit model for measure reductions, contractor quotes for installed costs, program award documents for incentives, and your utility tariff and regional eGRID factor for rates and emissions. The model does not assess moisture assemblies, asbestos, knob-and-tube wiring, radon, ventilation, or combustion safety.
FAQs
How much does weatherization typically save?
ENERGY STAR reports average savings of about 15% on heating and cooling costs, or 11% on total energy costs, for modeled cost-effective air sealing and insulation in typical existing U.S. homes. Those percentages use different cost bases and are benchmarks, not guarantees.
Should insulation or air sealing come first?
An assessment usually identifies and seals major leaks before insulation is added, especially in an attic, because insulation can hide leakage paths. Combustion-safety, moisture, radon, and ventilation needs should be checked before major tightening.
How do home age and climate affect savings?
Older, leakier, under-insulated homes and homes in more severe climates generally have more opportunity, while already efficient homes usually have less. Actual results also depend on fuel, equipment, behavior, and installation quality.
What does R-value mean?
R-value measures resistance to heat flow; a higher value generally insulates better. Recommended assemblies vary by climate, location in the building, material, and local code.
Do I need an energy audit or blower-door test?
Not for an early planning estimate, but an audit and blower-door test can locate leaks, quantify air leakage, improve savings assumptions, and identify safety or ventilation work before installation.
What projects count as weatherization?
Common projects include attic, wall, floor, crawl-space, and rim-joist insulation; whole-home and duct air sealing; weatherstripping; draft control; and sometimes storm windows or window improvements.
Why can windows have a longer energy-only payback?
Full window replacement is often expensive relative to the energy it saves when lower-cost sealing or insulation opportunities remain. Windows may still provide meaningful comfort, noise, durability, or maintenance benefits not counted here.
Can renters use this estimate?
Yes, for planning portable or landlord-approved measures. Renters should obtain permission before altering the building and should enter only costs and bill savings they expect to bear.
How do rebates affect payback?
Verified rebates, grants, and credits reduce net cost and usually shorten homeowner payback. Programs, funding, tax eligibility, and contractor requirements change, so verify every incentive with the administering agency before relying on it.