Can a Heat Pump Really Keep a House Warm When It’s –5 °C Outside?

 


Can a Heat Pump Really Keep a House Warm When It’s –5 °C Outside?

Short answer: yes — if the system and the house are designed properly.

Long answer: let’s unpack the physics, the myths, and the real-world experience (including plenty of UK winters).

❄️ The Big Misunderstanding

Many people imagine a heat pump as something that creates heat.
It doesn’t.

A heat pump moves heat — even when it feels bitterly cold outside.

At –5 °C, the outdoor air still contains a huge amount of thermal energy. A heat pump captures that energy and upgrades it to a usable temperature for your home.

This isn’t magic — it’s the same principle that lets your fridge extract heat from food.

🔬 How Heat Pumps Work in Cold Weather

  • The refrigerant boils at very low temperatures

  • It absorbs heat from air or ground

  • A compressor raises the temperature

  • That heat is released indoors

Modern UK-approved heat pumps are typically designed to operate down to –15 °C or even –20 °C.

🏠 The House Matters More Than the Heat Pump

This is where many horror stories come from.

A heat pump can absolutely keep a house warm at –5 °C if:

  • The house is well insulated

  • Draughts are controlled

  • Heat emitters (radiators or underfloor heating) are sized correctly

Trying to run a heat pump in a leaky, poorly insulated house is like trying to heat the garden.

🔥 “But Radiators Feel Cool…”

Heat pumps usually run at lower flow temperatures than gas boilers.

That means:

  • Radiators may feel warm, not hot

  • Heating runs for longer

  • Indoor temperature stays steady, not spiky

Comfort comes from stability, not roasting metal radiators.

⚡ Efficiency in the Cold

Yes, efficiency drops as it gets colder — but not catastrophically.

Typical winter performance:

  • 1 kWh of electricity → 3–4 kWh of heat

  • Even at –5 °C, most systems still outperform direct electric heating by a long way

And if your electricity is partly solar or off-peak? Even better.

🇬🇧 A Reality Check

Countries colder than the UK (Norway, Sweden, Finland) use heat pumps everywhere.

If heat pumps didn’t work below freezing:

  • Northern Europe would be freezing

  • The technology wouldn’t exist

✅ So… Can a Heat Pump Keep You Warm at –5 °C?

Yes — comfortably and reliably, provided:

  • Insulation is good

  • The system is properly designed

  • Expectations match how low-temperature heating works

A heat pump isn’t a drop-in boiler replacement.
It’s a whole-house heating strategy.


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