⚙ 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

🔥 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:

• EPA Power Profiler (U.S. ZIP-based grid lookup)