| System | Primary Energy Efficiency (%) | CO2 emissions (kg CO2/kWh heat) |
| Oil fired boiler | 60 – 65 | 0.45 – 0.48 |
| Gas fired boiler | 70 – 80 | 0.26 – 0.31 |
| Condensing gas boiler + low temperature system | 100 | 0.21 |
| Electrical heating | 36 | 0.9 |
| Conventional electricity + GHSP | 120-160 | 300-400 |
| Green electricity + GHSP | 0.20-027 | 0.00 |