Radiator Optimization - Summary
The heat transition is in full swing: heat pumps are increasingly replacing oil and gas heating. But for a heat pump to work efficiently, the radiators must be correctly sized.
The Problem: Old Radiators, New Heat Pump
Many existing buildings have radiators designed for high flow temperatures (65-75°C). Heat pumps, however, work most efficiently at low flow temperatures (35-55°C).
| Flow Temperature | Typical COP (Air-Water HP) | Electricity Consumption |
|---|---|---|
| 35°C | 4.5-5.0 | Very low |
| 45°C | 3.5-4.0 | Low |
| 55°C | 2.8-3.2 | Medium |
| 65°C | 2.2-2.6 | High |
The Rule of Thumb
Each degree Celsius lower flow temperature improves the annual performance factor (APF) by about 2.5%. Reducing from 55°C to 45°C saves around 25% electricity!
Radiator Types Compared
| Type | Plates | Convectors | Relative Output |
|---|---|---|---|
| Type 11 | 1 | 1 | 63% |
| Type 22 | 2 | 2 | 100% |
| Type 33 | 3 | 3 | 135% |
By replacing a Type 11 radiator with a Type 33 at the same size, you can increase output by factor 2.25 – without changing the pipework!