Heat Pump vs. Natural Gas Boiler: Carbon Emissions by Grid Source
⚙ Heat Pump vs. Natural Gas Boiler: Which Has the Lower Carbon Footprint?
When it comes to reducing carbon emissions in buildings, the choice between using a heat pump or a natural gas boiler isn’t just about equipment efficiency — it’s also about the source of electricity powering the heat pump.
This post compares both technologies under two electricity supply scenarios: one where the grid is powered by natural gas and another where it’s powered by coal.
↻ The Basic Comparison: Efficiency and Emissions
| System | Typical Efficiency | Emission Source |
|---|---|---|
| Heat Pump (air-source) | COP = 3.0 (300% efficient) | Grid electricity |
| Natural Gas Boiler | AFUE = 0.90 (90% efficient) | On-site combustion |
🔥 Scenario 1: Heat Pump Powered by Natural Gas–Fired Electricity
Assumptions:
- Heat pump COP = 3.0 → 1 kWh electricity → 3 kWh heat
- Electricity EF = 0.4 kg CO₂e/kWh
- Boiler EF = 5.3 kg CO₂e/therm ≈ 0.181 kg CO₂e/kWh heat (after 90% efficiency)
Results:
- Heat Pump: 1 kWh heat = 1/3 kWh electricity = 0.133 kg CO₂e
- Boiler: 1 kWh heat = 0.181 kg CO₂e
🏭 Scenario 2: Heat Pump Powered by Coal-Based Electricity
Assumptions:
- Electricity EF = 1.0 kg CO₂e/kWh (typical for coal)
Results:
- Heat Pump: 1 kWh heat = 1/3 kWh electricity = 0.333 kg CO₂e
- Boiler: 1 kWh heat = 0.181 kg CO₂e
⚡ What This Means
- If your grid is clean or average (≤0.5 kg CO₂e/kWh) → Heat pumps are typically lower carbon.
- If your grid is coal-heavy (≥0.8 kg CO₂e/kWh) → Natural gas boilers may be cleaner in the short term.
🧠 Bottom Line
Heat pumps aren’t always lower-carbon than natural gas. It depends on how clean the electricity is. As the grid decarbonizes, the carbon advantage of heat pumps will continue to grow.
Pro Tip: Before choosing your system, check your local emission factor:
Bob Fassbender is the founder of Energy-Models.com and Fassbender Energy Advisory. A former Trane software engineer and instructor, Bob has more than 20 years of experience in energy modeling, building performance, utility incentives, and energy strategy. His work spans whole-building energy modeling, calibration, independent technical review, decarbonization planning, utility incentive strategy, renewable energy analysis, and owner advisory services. Bob has supported projects ranging from commercial buildings and utility programs to large-scale data center developments involving power infrastructure, geothermal systems, heat recovery, and long-term energy planning. Through Energy-Models.com, Bob has trained thousands of energy professionals in eQUEST, OpenStudio, EnergyPlus, LEED modeling, and building performance analysis. He continues to advise owners, engineers, architects, and developers on energy-related decisions while exploring emerging technologies such as artificial intelligence, machine learning, and advanced building analytics.