The Challenge with Existing Radiators
Gas boilers typically run at flow temperatures of 60–80°C. Heat pumps run most efficiently at 35–55°C. A radiator sized for 70°C will under-heat the room when supplied with 45°C water, as it emits significantly less heat at lower temperatures.
Assessing Your Existing Radiators
Whether your existing radiators are adequate depends on their physical size, the heat loss of each room, and the design flow temperature. An MCS heat loss survey identifies rooms where radiators need upgrading.
When You Need to Upgrade
Radiator upgrades are needed when:
- Existing radiators are small
- Rooms have high heat loss
- The target flow temperature is low for maximum efficiency
Low-Temperature Radiator Options
- Fan-assisted radiators: add a fan to dramatically increase output at low temperatures
- Larger flat panel radiators: simply bigger standard radiators
The High-Temperature Option
Some heat pump models (e.g., Daikin Altherma 3 H HT) produce flow temperatures up to 65°C, making them compatible with existing radiators without replacement.
Sources: the £7,500 grant.
