People talk about needing larger radiators for heat pumps. You also needed similar sized radiators for condensing gas boilers to work at the claimed efficiency.
People were just burning 20% more gas for no good reason.
For heat pumps, 40 degrees is about the max for efficient operation. So radiators need to be quite a bit bigger compared to what you need for a condensing boiler.
So if a new system got installed and sized for running at 60, then it's losing 10-20 percent efficiency.
https://www.theheatinghub.co.uk/articles/turn-down-the-boile...
> The correct temperature setting for heating on a combi boiler is 'as low as possible', but as a guide most older homes can run their heating systems at 60°C and newer homes at 50-55°C. They start to reach their very highest efficiency potential at 45°C flow temperature or lower, but this can be too low for older properties.
> Ultimately how low you can turn your flow temperature down will depend on the size of your radiators, how well insulated your home is and your thermostat temperature.
....
> A vast skills and knowledge gap (that dates back to 2005 when condensing gas boilers become mandatory) means 99% of installers do not understand how condensing gas boilers work and therefore cannot set them up to run as they were designed to. Installers have been let down and so have UK households. We have simply not benefited as much as we should have from this leap forward in boiler efficiency.
If you go lower, efficiency may increase by tiny amounts, but in most practical setups the system is likely to become unstable and you will lose more than you gain. This is especially true if the system is also used to provide hot tap water. For hot tap water, in particular for a shower, the system needs to be able to heat a lot of water quickly.
> NB turning down your heating flow temperature is separate to setting your hot water temperature, but we cover that too - see section 11