How does the air sealing carbon savings calculation work?

For each energy source, annual heating and cooling use is multiplied by the entered energy-reduction percentage. Avoided energy is then multiplied by the selected carbon dioxide factor, and the source totals are added.

What energy reduction percentage should I use?

Use a measure-specific estimate from a home energy audit, calibrated model, or post-project utility analysis when possible. The initial 7% is only an editable example and is not a national air-sealing claim.

Does a 25% blower-door leakage reduction mean 25% energy savings?

No. ACH50 leakage reduction is not the same as whole-home heating and cooling energy reduction because conductive heat flow, equipment efficiency, weather, natural infiltration, internal gains, and behavior also affect energy use.

Does this include upstream or embodied emissions?

No. The default method estimates operational carbon dioxide using electricity and direct fuel factors. It excludes sealant and material manufacturing, contractor travel, upstream fuel emissions, refrigerant leakage, and disposal.

Can air sealing create indoor-air or combustion risks?

Yes. Tightening can affect ventilation, moisture, radon, fireplaces, and combustion appliances. A qualified energy auditor or HVAC professional can assess ventilation and combustion safety before major work.

Home Air Sealing Carbon Savings Calculator

Estimate how much operational carbon dioxide could be avoided when air sealing reduces heating and cooling energy. Enter the HVAC portion of annual energy use—not whole-house energy unless it is all for heating and cooling. Everything runs locally in your browser and inputs are not tracked.

Last reviewedAugust 3, 2026

Core methodHVAC energy × reduction % × CO₂ factor

Best inputAudit or calibrated measure-specific reduction

PrivacyNo server upload or input tracking

Before using the estimate

Use HVAC energySeparate heating and cooling kWh or fuel from lighting, appliances, hot water, taxes, and fixed charges.

Use a measured reductionAn audit result is stronger than a generic percentage. The loaded 7% is an editable example only.

Plan for safetyMajor tightening can require ventilation, moisture, radon, and combustion-safety checks.

Energy and air-sealing inputs

1. Expected result and period

Expected HVAC energy reduction (%) Editable air-sealing-only example; use an audit value when available. Analysis period (years) Assumes annual use, reduction, and factors stay constant.

2. Annual heating and cooling energy before sealing

The loaded values are a mixed-fuel example, not a household average. Replace them with annual HVAC usage from bills or an audit.

Electricity (kWh/year) Cooling, heat-pump, resistance-heat, and HVAC auxiliary electricity only. Natural gas (therms/year) Space-heating gas only; exclude water heating and cooking. Heating oil (gallons/year) Enter zero if not used for space heating. Propane (gallons/year) Space-heating propane only.

3. Optional blower-door context

Enter both ACH50 readings to display measured leakage reduction. This does not automatically set energy savings because leakage and HVAC energy do not change one-for-one.

Before sealing (ACH50) Air changes per hour at 50 pascals before work. After sealing / target (ACH50) Post-work measurement or target at the same test pressure.

Advanced emissions factors

U.S. starting factors estimate operational CO₂. Electricity varies substantially by grid and accounting method; replace it with an appropriate regional average or avoided-emissions factor.

Electricity (kg CO₂/kWh) Natural gas (kg CO₂/therm) Heating oil (kg CO₂/gallon) Propane (kg CO₂/gallon)

Estimated result

Annual operational CO₂ avoided — Enter valid energy use to calculate.

Planning limit: Results are arithmetic estimates, not a building simulation, emissions inventory, guarantee, or substitute for a home energy and safety assessment.

How the estimate works

The calculator applies one measure-specific percentage to each entered heating and cooling energy source. That assumes air sealing reduces each source proportionally. If an audit gives separate heating and cooling reductions, calculate them separately or use a weighted combined percentage.

Energy saved by source = annual HVAC energy × energy reduction % CO₂ saved by source = energy saved × source emission factor Total annual CO₂ saved = electricity + natural gas + heating oil + propane savings Period CO₂ saved = annual CO₂ saved × analysis years Optional leakage reduction = (before ACH50 − after ACH50) ÷ before ACH50 × 100

The multi-year result holds energy use, weather, occupancy, equipment, and carbon factors constant. It does not model grid decarbonization, fuel switching, rebound effects, degradation, or future changes to the home.

Assumptions and sources

Input	Value	Source and scope
Energy reduction	7% loaded example	Starlight Tools illustrative air-sealing-only input, not a national benchmark. Replace with an audit or calibrated model.
Package benchmark	15% HVAC cost average	ENERGY STAR methodology for modeled cost-effective air sealing plus insulation in typical existing U.S. homes; not used automatically.
Electricity	0.348 kg CO₂/kWh	EPA eGRID 2023 U.S. total output rate of 767.25 lb/MWh, converted to kg/kWh. It is an average generation factor, not a marginal avoided-emissions forecast, and excludes delivery losses.
Natural gas	5.30 kg CO₂/therm	EPA equivalencies calculations and references; direct combustion CO₂.
Heating oil	10.19 kg CO₂/gallon	EPA household carbon calculator assumptions; 22.46 lb CO₂/gallon for distillate fuel oil.
Propane	5.75 kg CO₂/gallon	EPA household carbon calculator assumptions; 12.68 lb CO₂/gallon for LPG propane.

Sources reviewed August 3, 2026. Default fuel factors cover direct combustion CO₂; upstream extraction, processing, transmission, leakage, and embodied project emissions are excluded.

Air sealing, measurement, and safety

Start with the right bill data

A heating-season baseline can include weather differences and unrelated loads. A utility bill disaggregation or audit model is more reliable than assigning the whole annual bill to HVAC.

ACH50 is not energy savings

A blower door measures leakage under test pressure. It helps find and verify leaks, but conversion to natural infiltration and energy depends on climate, exposure, building height, and the thermal model.

Pair tightening with ventilation

DOE air-sealing guidance says air sealing and ventilation go hand in hand. Qualified help is especially important around fuel-burning equipment, fireplaces, moisture, and radon.

FAQs

How does the carbon calculation work?

Each annual HVAC energy input is multiplied by the entered reduction percentage and its CO₂ factor. The four source results are then added.

What reduction percentage should I use?

Prefer a measure-specific estimate from a home energy audit, calibrated model, or normalized post-project analysis. The initial 7% is only an editable example.

Is the ENERGY STAR 15% benchmark for air sealing alone?

No. It covers a modeled package of cost-effective air sealing and insulation in typical existing U.S. homes. It should not be entered as an air-sealing-only result unless an audit supports it.

Does a 25% ACH50 reduction equal 25% HVAC energy savings?

No. Leakage is one part of the heating and cooling load. Conduction, equipment efficiency, weather, solar and internal gains, and behavior also matter.

Should I use an average or marginal electricity factor?

An average grid factor is useful for inventory-style attribution. A marginal or non-baseload factor may better represent the generation that changes when demand is reduced. Use the factor that matches your purpose and location, and label the result accordingly.

What emissions are excluded?

The default result excludes upstream fuel emissions, methane leakage, refrigerants, manufacturing and delivery of sealing materials, contractor travel, maintenance, and disposal.

Can tightening a home be unsafe?

It can affect ventilation, moisture, radon, fireplaces, and combustion appliances. Consider a professional assessment, blower-door testing, combustion-safety checks, and code-required ventilation before major tightening.