Heat Pump Carbon Savings Calculator

Heat pump carbon savings depend on what system you’re replacing and your electricity grid mix:

• Gas boiler to ASHP: Save 20-24 tonnes CO₂ over 20 years (1.0-1.2 tonnes/year)
• Oil boiler to ASHP: Save 30-35 tonnes CO₂ over 20 years (1.5-1.7 tonnes/year)
• LPG to ASHP: Save 18-22 tonnes CO₂ over 20 years (0.9-1.1 tonnes/year)
• Storage heater to ASHP: Save 5-8 tonnes CO₂ over 20 years (0.25-0.4 tonnes/year)

Key factor: The cleaner your electricity grid becomes, the greater the savings. UK grid carbon intensity has fallen from 0.43 kg CO₂/kWh in 2015 to 0.233 in 2024, meaning new heat pumps save even more carbon than older ones.

Manufacturing and installation do produce emissions, but the payback is quick:

• Manufacturing emissions: 5-8 tonnes CO₂ for the heat pump unit itself
• Installation carbon: 2-3 tonnes CO₂ (materials, transport, labor)
• Total embodied carbon: 7-11 tonnes CO₂
• Carbon payback period: 2.5-3.5 years (when switching from gas boiler)

Real example: A 10-tonne embodied carbon ASHP saves 1.2 tonnes CO₂/year when replacing a gas boiler. This means the system “pays back” its manufacturing carbon in just 8-9 years, with 11-12 years of pure carbon savings remaining in a typical 20-year lifespan.

The UK grid is becoming cleaner every year, which means heat pumps save MORE carbon over time:

• 2024 grid: 0.233 kg CO₂/kWh (58% fossil fuels, 42% renewables)
• 2030 grid (target): 0.15-0.17 kg CO₂/kWh (70% clean energy)
• 2050 grid (target): Near-zero kg CO₂/kWh (100% clean energy)
• Impact: A heat pump installed today will save 30-40% MORE carbon in year 15-20 than in years 1-5

Real projection: A heat pump saving 1.2 tonnes CO₂/year from 2024-2029 may save 1.5+ tonnes/year from 2035-2040 as the grid decarbonises, even though it uses the same electricity. This calculator uses a 2.5% annual improvement rate (conservative UK forecast).

Tree equivalence is a useful way to visualize carbon savings, but comes with important caveats:

• Average mature tree absorption: 15-25 kg CO₂ per year (varies by species, age, climate)
• Calculator uses: 20 kg CO₂/year as middle estimate
• A 1.2 tonne/year heat pump = planting 60 trees annually
• 20-year savings of 24 tonnes = equivalent to 1,200 tree years

Important note: Trees store carbon over decades and can release it if cut down or burned. They’re valuable for climate and ecology but can’t replace reducing emissions directly. Think of tree planting as additional benefit, not replacement for switching to heat pumps.

GSHP has slightly better carbon performance but the difference narrows over time:

• ASHP annual savings: 1.2 tonnes CO₂ (COP 3.5 average)
• GSHP annual savings: 1.35 tonnes CO₂ (COP 4.2 average)
• 20-year difference: About 3 tonnes CO₂ (GSHP ahead)
• However: Installation carbon of GSHP (14-16 tonnes) is higher than ASHP (7-10 tonnes)
• Net result: Carbon payback is similar (2.5-3 years) because GSHP carbon advantage offsets slightly higher manufacturing

Practical conclusion: Install whichever system suits your property (GSHP needs space, ASHP suitable for apartments). Both save substantial carbon. GSHP is marginally better environmentally but ASHP is more accessible and still excellent for carbon reduction.

This calculator includes grid decarbonisation projections to show realistic future carbon benefits:

• Default setting: 2.5% annual reduction in grid carbon intensity
• What this means: Each year, the same kWh of electricity produces less CO₂
• Year 1 grid: 0.233 kg CO₂/kWh
• Year 10 grid: 0.181 kg CO₂/kWh (22% cleaner)
• Year 20 grid: 0.141 kg CO₂/kWh (39% cleaner)

Why it matters: Without accounting for grid improvement, carbon savings would be underestimated. A heat pump installed today will save progressively MORE carbon as the grid decarbonises, making it a better investment year on year. You can adjust the percentage in the calculator to match your own assumptions.