Do Heat Pumps Work in Freezing Temperatures? UK Reality Explained

A common question every winter is:

“Do heat pumps actually work when it’s freezing?”

Short answer — yes.

But they don’t behave the same way they do in mild autumn weather, and that’s where a lot of confusion comes from.

Yes, Heat Pumps Work Below 0°C

An air source heat pump doesn’t “stop working” at 0°C.

It extracts heat from the outside air using refrigerant, and there is still usable heat energy in the air even at 5°C or lower. Countries like Norway and Sweden use heat pumps in much colder climates than the UK without issues.

So freezing temperatures alone are not a problem.

What Changes When It Gets Cold?

What does change is how hard the system has to work.

When it’s freezing outside:

• The house is losing heat faster

• The heat pump’s output capacity reduces slightly 

• The efficiency (COP) drops 

• Electricity usage increases

That’s normal.

If it’s 10°C outside, your system might be running at a COP of 3.5 or more.
At -2°C, that might drop closer to 2.0–2.5, depending on the flow temperature.

That doesn’t mean it’s failing. It just means it’s working harder.

Why Winter Bills Look Higher

Most annual heating energy is used between October and March, with December and January usually being the heaviest months.

If your heat pump is set up correctly, you’ll still see seasonal efficiency (SCOP) of around 2.5–3.0 across the year.

But in the coldest months, daily electricity use will naturally increase because:

• Heat demand is higher 

• Efficiency is lower 

• Hot water use often increases 

The key question isn’t “is it using more?”
It’s “is it using a reasonable amount for the size and insulation level of the property?”

What Is Not Normal

Freezing weather shouldn’t cause:

• The house is failing to reach the desired temperature 

• The immersion heater is running constantly

• Flow temperatures pushed up to 55°C+

• The system is rapidly turning on and off

Those usually point to sizing or setup issues rather than outside temperature alone.

So Should You Worry?

If your home stays warm and comfortable, and your winter usage is roughly in line with what you’d expect for the property size, the system is probably doing what it should.

If it struggles to maintain temperature or your winter electricity use seems excessive, it may be worth reviewing:

• The heat loss calculation 

• The design flow temperature 

• Weather compensation settings 

• Emitter sizing 

Freezing temperatures don’t stop heat pumps from working, but a poor setup will show itself very quickly in cold weather.