One of the most important factors in how well a heat pump performs.
Flow temperature is one of the biggest influences on how efficiently a heat pump runs. Many homeowners don’t realise that the temperature the system runs at can have a major impact on both running costs and comfort.
Flow temperature is the temperature of the water leaving the heat pump and travelling into your heating system (either radiators or underfloor heating pipes).
Gas boilers traditionally run at quite high flow temperatures — often 60–80°C. Heat pumps are designed to run much cooler, usually between 35°C and 45°C. This is one of the main reasons they can be more efficient than boilers, but it also changes how the rest of the system needs to be designed.
The cooler the water the heat pump has to produce, the less electricity it uses. Running at lower flow temperatures is one of the most effective ways to keep running costs down.
If you want to run your heat pump at low flow temperatures, your radiators or underfloor heating must be capable of delivering enough heat at those lower temperatures. This is why proper sizing of emitters is so important.
Systems that are forced to run at higher flow temperatures (because the emitters are too small) lose much of their efficiency advantage. This is one of the most common reasons heat pumps don’t perform as well as expected.
Larger radiators or underfloor heating allow the system to run at lower temperatures while still keeping your home warm. This is often more important than people realise.
Some systems are set up to run at unnecessarily high flow temperatures. Getting the controls and weather compensation set correctly can often improve efficiency without any hardware changes.
Use our Heat Pump Estimator to get a realistic picture based on your property.