What Flow Temperature Should My Heat Pump Run At?

Introduction

Flow temperature is one of the most important settings in a heat pump system.

Set too high, and efficiency drops dramatically.
Set too low, and your home may struggle to reach the desired temperature.

Unlike gas boilers, heat pumps are designed to run at lower flow temperatures for longer periods.

Understanding the correct range for your system can make a significant difference to comfort and running costs.

Typical Flow Temperature Ranges

While every system is different, most domestic heat pumps operate within these ranges:

Underfloor Heating:
30–40°C

Radiator Systems (designed for heat pumps):
35–50°C

Older radiator systems may require slightly higher temperatures, but consistently running at 60–65°C will significantly reduce efficiency.

Why Lower Is Better

Heat pumps become less efficient as flow temperature increases.

The higher the temperature lift (difference between outside air and flow temperature), the harder the compressor has to work.

This reduces COP (Coefficient of Performance) and increases electricity consumption.

As a general rule:

Lower flow temperature = Higher efficiency

But only if your emitters (radiators or underfloor loops) are correctly sized.

Why Some Systems Run at 60–65°C

There are usually three reasons:

1. Radiators are undersized

2. Weather compensation isn’t set correctly 

3. The system was commissioned conservatively 

In some cases, installers increase flow temperature to guarantee comfort quickly — but this can mask design issues.

Weather Compensation and Flow Temperature

Modern systems adjust flow temperature automatically based on outdoor temperature.

Instead of running at one fixed setting, the system follows a curve.

On milder days, the flow temperature should reduce.
On colder days, it increases gradually.

If your system runs at a fixed 55–60°C all winter, weather compensation may not be configured properly.

When Higher Temperatures Are Acceptable

There are limited scenarios where higher flow temperatures are used:

• Legionella cycles for hot water cylinders 

• Extreme cold conditions 

• Poorly insulated properties 

However, these should be exceptions, not daily operations.

Final Thoughts

Most well-designed heat pump systems run efficiently between 35–50°C for space heating.

If your system is consistently running above this range, it may indicate:

• Incorrect emitter sizing

• Conservative commissioning 

• Weather compensation is not configured correctly

Flow temperature is one of the biggest drivers of efficiency and running costs.

If your electricity bills are higher than expected, you may also want to read:
Why Is My Heat Pump Using So Much Electricity?

Getting flow temperature right can dramatically improve comfort and reduce running costs.

If you’d like your settings reviewed properly, you can book a structured heat pump review here.