Compare annual CO2 emissions for gas and heat pump heating systems
How to Use This Tool
Follow these steps to generate accurate carbon emission comparisons for your property:
- Enter your property's annual useful heat demand in kWh or MWh. This is the total heat required to warm your home each year, typically available from energy bills or HVAC load assessments.
- Adjust gas heating parameters: set your boiler's AFUE efficiency (default 90% for modern condensing boilers) and your region's gas carbon intensity, or select a region from the dropdown to auto-fill default values.
- Adjust heat pump parameters: set your heat pump's COP (default 3.5 for modern air source heat pumps) and your local grid's electricity carbon intensity.
- Click Calculate to view detailed emission breakdowns for both systems, including annual savings and percentage reduction.
- Use the Reset button to clear all inputs and start over, or Copy Results to save the output to your clipboard.
Formula and Logic
The tool calculates annual carbon emissions for both heating systems based on equivalent useful heat output to ensure fair comparison:
Gas Heating Emissions
Gas Consumed (kWh) = Annual Heat Demand / (Boiler Efficiency / 100)
Gas Emissions (kg CO2e) = Gas Consumed * Gas Carbon Intensity (kg CO2e/kWh gas)
Heat Pump Emissions
Electricity Consumed (kWh) = Annual Heat Demand / Heat Pump COP
Heat Pump Emissions (kg CO2e) = Electricity Consumed * Electricity Carbon Intensity (kg CO2e/kWh electricity)
Comparison Metrics
Annual Savings = Gas Emissions - Heat Pump Emissions
Percentage Reduction = (Annual Savings / Gas Emissions) * 100
All values are converted to both kilograms and tonnes of CO2 equivalent for readability.
Practical Notes
Several real-world factors can affect the accuracy of these estimates:
- Emission factors vary significantly by region: gas carbon intensity depends on extraction and transportation methods, while electricity intensity depends on local grid mix (e.g., coal-heavy vs renewable-heavy grids). Use the region dropdown to apply regional averages, or input custom values from your local energy provider.
- This tool calculates operational emissions only. Lifecycle emissions (manufacturing, installation, disposal of equipment) are not included: heat pumps typically have higher upfront lifecycle emissions than gas boilers, but these are offset by lower operational emissions within 5-10 years of use.
- Heat pump COP values vary with outdoor temperature: cold climate heat pumps maintain higher COP in freezing conditions, while standard models may drop to COP 2 or lower in sub-zero weather. Adjust COP to match your local climate.
- Boiler efficiency (AFUE) decreases with age: older boilers may have efficiency as low as 60%, while modern condensing boilers reach 95-98%.
Why This Tool Is Useful
This tool serves multiple audiences across the sustainability sector:
- Homeowners can assess whether switching to a heat pump will reduce their household carbon footprint, and estimate annual emission savings to support retrofit decisions.
- Sustainability professionals can model emission scenarios for client properties, or evaluate the impact of heat pump adoption at scale for corporate net-zero plans.
- Policy advocates can use the tool to demonstrate the emission reduction potential of heat pump incentives, using regional grid data to support policy proposals.
- Researchers can adjust parameters to test sensitivity of emission savings to grid decarbonization, heat pump efficiency improvements, or boiler efficiency standards.
Frequently Asked Questions
How do I find my property's annual heat demand?
Check your annual energy bills for total gas consumption in kWh, then multiply by your boiler's efficiency (e.g., 10,000 kWh gas * 0.9 efficiency = 9,000 kWh useful heat demand). Alternatively, use a HVAC load calculation from a licensed contractor, or refer to average values for your property size and climate zone.
Do heat pumps save carbon emissions if my grid uses coal power?
It depends on your local grid intensity and heat pump COP. For example, a heat pump with COP 3 on a grid with 0.8 kg CO2e/kWh electricity will emit 0.267 kg CO2e per kWh heat, while a 90% efficient gas boiler emits 0.203 kg CO2e per kWh heat (using 0.183 kg CO2e/kWh gas). As grids decarbonize, heat pump emission savings increase over time.
Why doesn't the tool include lifecycle emissions?
Operational emissions account for 80-90% of total heating-related emissions over a 15-year period for most systems. Lifecycle emissions vary widely by equipment model and manufacturing location, so we focus on operational emissions which are more consistent and easier to measure for users. We recommend consulting lifecycle assessment reports for specific equipment models if needed.
Additional Guidance
For the most accurate results, source emission factors directly from your local energy provider or regional environmental agency. The US EPA, EU Climate Action, and UK BEIS publish annual grid intensity data for major regions.
Re-run the calculation with future grid intensity values (e.g., 2030 projected grid mix) to estimate how heat pump emission savings will grow as your local grid decarbonizes.
Combine this tool with home insulation assessments: reducing heat demand by improving insulation will lower emissions for both heating systems, and improve heat pump efficiency in cold weather.