The cold weather question is probably the one that gives Lancashire homeowners the most pause when they’re considering an air source heat pump. It’s understandable. If the technology extracts heat from outside air, what exactly happens when that outside air gets bitterly cold? And can you really rely on it during a proper freeze?
The short answer is yes — but understanding the detail is worth it.
What temperature can a heat pump operate down to?
Modern air source heat pumps are designed to work effectively at temperatures well below freezing. Most units from established manufacturers will continue to produce useful heat down to around -15°C to -20°C. Some are rated to -25°C.
Lancashire winters are rarely kind, but they’re also not Arctic. The region typically sees overnight lows of around -5°C to -10°C during a cold spell, with extended periods below -15°C being genuinely unusual. The heat pump should handle typical Lancashire winters without issue.
The nuance is efficiency. A heat pump is most efficient when the difference between the outside temperature and the target indoor temperature is smallest. At 7°C outside, a heat pump might achieve a COP (coefficient of performance) of 3.5 — meaning 3.5 units of heat for every unit of electricity used. At -5°C, that COP might drop to 2.0 or 2.5. Still efficient compared to direct electric heating, but less so than in milder conditions.
Defrost cycles — what they are and why they happen
When outside temperatures drop below about 5°C and humidity is high, frost can form on the outdoor unit’s heat exchanger. This is a normal part of heat pump operation — not a sign that something is wrong.
When the unit detects frost build-up, it enters a defrost cycle. During this cycle, the heat pump temporarily reverses its operation to warm the outdoor coil and melt the ice. The cycle typically lasts between 5 and 15 minutes, and during this time the unit isn’t producing as much heat for your home.
Modern systems manage this intelligently. The indoor heating circuit retains enough warmth in the pipework and hot water cylinder to ride through a defrost cycle without any noticeable drop in comfort. You won’t feel it happening in a well-sized system — the house just stays warm.
The frequency of defrost cycles depends on outside conditions. On a cold, humid day you might see several over a few hours. On a cold, dry day there may be very few. Either way, it’s a managed process, not a problem.
How does output change in very cold weather?
As outside temperatures fall, the heat pump has to work harder to extract heat from the air. Its output (the amount of heat it delivers) typically decreases slightly, while its electricity consumption increases. This is called the ‘capacity curve’ and every heat pump has one.
A properly designed system accounts for this. The heat pump is sized not just for average winter conditions but for design conditions — typically around -3°C for most of Lancashire. This means that on all but the very coldest nights, the heat pump alone should be able to maintain your home’s temperature.
For extreme cold snaps that go beyond design conditions, most heat pump systems include a backup or supplementary heater — often an electric immersion element — that cuts in automatically if the heat pump can’t keep up alone. This is sometimes called a ‘bivalent’ or hybrid approach. The backup heater uses more electricity per unit of heat than the heat pump, but it only runs when conditions genuinely demand it.
What about homes that are harder to heat?
Older properties with solid walls and limited insulation have higher heat demand — which puts more pressure on any heating system in cold weather. A heat pump that’s correctly sized for such a property will still cope, but there’s less margin for error.
This is why the design process matters so much. A heat pump sized by guesswork or based purely on the square footage of a house without considering fabric heat loss can struggle in cold weather. A heat pump sized from a proper room-by-room heat loss calculation will be specified to handle the worst your local climate throws at it.
If your home has areas of poor insulation that are being addressed over time, a slightly larger heat pump or a well-integrated backup element provides a sensible buffer.
Real-world experience in the UK north west
Air source heat pumps have been installed across the north of England for long enough now that there’s a solid base of real-world experience in similar climates to Lancashire. The feedback from households who’ve had systems properly installed is consistently positive, including through winters with extended cold periods.
The homes that occasionally have issues are almost always those where the system was undersized, or where the installer didn’t carry out a proper heat loss survey. A cheap quote often reflects a quick design — and quick designs tend to create problems in the coldest weeks of the year.
Wise Energy Solutions carries out full heat loss surveys before specifying any heat pump, and we design for Lancashire conditions — not just average UK weather. We cover Blackpool and the Fylde Coast, Preston and South Ribble, and Burnley and Pendle, and we’ll be straight with you about what your home needs to stay reliably warm through winter.
Want a heat pump designed properly for a Lancashire winter? Call 01253804151 or visit wiseenergy.co.uk.