Carbon Accounting Rules of Thumb for Energy Modelers
When estimating carbon emissions, project savings, or lifecycle impact, these rules of thumb provide fast, approximate values for early-stage planning and model review.
Quick Reference Table
Rule of Thumb
Typical Value
Notes
Social cost of carbon (SCC)
$50 per metric ton CO₂e
Used in U.S. federal and utility planning; varies from $40–$150 depending on policy context
1 gallon of fuel oil #2
10.15 kg CO₂e
EPA default value
1 gallon of propane
5.75 kg CO₂e
EPA default value
1 kWh from U.S. average grid
~0.4 kg CO₂e
Use regional factors for accuracy (see eGRID)
1 metric ton CO₂e
~2,205 pounds
1 metric ton = 1,000 kg
1 short ton (U.S.)
~0.91 metric tons CO₂e
1 short ton = 2,000 lbs
Heat pump vs. boiler crossover point
Grid EF < 0.6 kg CO₂e/kWh
Below this, heat pumps are typically lower-carbon than gas boilers
Lighting retrofit (LED vs. fluorescent)
~0.5–2.0 tons CO₂e/year per 10,000 ft²
Varies by occupancy, hours, and lighting baseline
Roof insulation upgrade (e.g. R-10 to R-30)
~0.5–1.5 tons CO₂e/year per 10,000 ft²
Higher in colder climates; impact depends on heating type
HVAC upgrade (e.g. RTU to VAV system)
~2–4 tons CO₂e/year per 10,000 ft²
More savings in variable load zones and multi-zone systems
Use these values for quick sanity checks, back-of-envelope screening, and storytelling during early-phase energy modeling or decarbonization planning.