Heating
There is a stubborn myth doing the rounds that heat pumps do not work when it gets cold. It sounds almost reasonable. How can you pull warmth out of freezing air. Surely once the frost arrives the thing gives up. It is a fair question and it deserves a proper answer, because the myth puts people off a system that would heat their home beautifully through a North-East winter.
The short version is that air source heat pumps work perfectly well in cold weather, and they do it every winter in homes far colder than ours. The longer version is worth your time because once you understand the physics the worry disappears. Here is how it actually works.
There is heat in cold air
The idea that cold air has no heat in it feels true but it is not. Heat is just energy, and air only runs out of it entirely at a temperature far, far below anything Britain ever sees. Air that feels bitter to you on a frosty morning is still carrying a great deal of energy. It is simply at a low temperature by human standards.
A heat pump does not need warm air to work. It needs air that is warmer than the refrigerant flowing through it, and the clever part is that the refrigerant is made to run colder still. Even on a frosty day the outside air is far warmer than that refrigerant, so heat flows from the air into the system exactly as it should. That is the whole trick, and it is why a heat pump keeps gathering heat long after you would swear there was none left to gather.
Think of it the way heat always behaves. Heat only ever flows from something warmer to something colder, never the other way of its own accord. A cup of tea goes cold because its heat escapes into the cooler room around it. The heat pump uses that same one-way flow. By keeping the refrigerant colder than even frosty outdoor air, it guarantees that heat flows out of the air and into the system, every time, whatever the thermometer says. There is no temperature our weather reaches where that stops being true. The air would have to drop to a level no British winter has ever come close to before the heat ran out.
The refrigerant cycle in plain terms
You do not need to be an engineer to follow how it works. The system moves a special fluid, the refrigerant, round a loop in a continuous cycle, and at each stage something useful happens.
- It takes in heat outside. In the outdoor unit the refrigerant is colder than the outside air, so heat flows from the air into it. This makes the refrigerant boil into a gas even though it is cold, because it boils at a very low temperature.
- It gets squeezed. A compressor squeezes that gas, and squeezing a gas heats it up sharply. Now the refrigerant is properly hot, hot enough to warm your rooms.
- It gives up heat inside. Indoors the hot gas passes its heat into your room air, warming the house, and as it loses heat it turns back into a liquid.
- It resets. The liquid passes through a valve that drops its pressure and temperature right back down, ready to go outside and soak up more heat.
Round and round it goes. Nothing is burned. The system is simply collecting heat that already exists outside, concentrating it by squeezing the refrigerant and releasing it indoors. Because it is moving heat rather than making it, one unit of electricity delivers several units of warmth into your home.
The compressor is the only part really drawing power, and even that is modest. Everything else is just the refrigerant doing what refrigerants do, boiling and condensing round the loop. The genius of the design is that most of the heat you feel in the room never came from your electricity meter at all, it came from the air outside for nothing. Your electricity is only paying to gather it up and move it, which is a far smaller job than making the heat from scratch. That is the single idea that explains why a heat pump keeps your home warm in winter without a frightening bill behind it.
Performance down to low temperatures
A reasonable follow-up is whether it works as well at freezing as it does on a mild day. The honest answer is that efficiency does ease off as the air gets colder, because there is a bit less heat to gather and the system works a little harder to gather it. But easing off is a long way from stopping.
Modern air source heat pumps are built and rated to keep heating at temperatures well below freezing, far colder than a typical North-East winter. On a frosty morning yours will still be pulling plenty of heat from the air and keeping the house warm. Even on its least efficient cold day it is usually still moving more heat per unit of electricity than direct electric heating could ever manage. The drop in efficiency is real but it is gentle, and across a whole local winter the system spends most of its time in mild damp conditions where it performs strongly.
It is worth putting that drop in perspective. Even if the efficiency slides from around four down towards two or so on the very coldest morning of the year, a ratio of two still means you are getting twice the heat out that a plain electric heater would give you for the same power. In other words the heat pump at its worst is still comfortably ahead of the alternatives at their best. And those bitter mornings are a handful of days a year here, not the norm. For the great majority of the winter the system sits up in its efficient range doing exactly what it is designed to do. Sizing is the thing that matters most. A system matched properly to the home has the output in hand to keep you warm even on the coldest days, which is another reason the survey is not a formality.
Why defrost cycles are normal
When the outdoor air is cold and damp, a little frost can build up on the outdoor coil as the unit draws heat and moisture condenses and freezes. Left alone that frost would eventually get in the way. So the system clears it with a defrost cycle.
For a few minutes the heat pump briefly reverses, sends warmth out to the outdoor coil and melts the frost away, then returns to normal heating. You might see the indoor warmth pause, notice steam rising off the outdoor unit as the frost melts or hear the sound change. All of that is the system working exactly as designed. A defrost runs only when it is needed and it is over quickly. It is not a fault and it is not a sign the system is struggling, it is simply good housekeeping built in. The only thing to watch for is a unit that stays frozen solid for a long time, which is worth a call.
Siting the outdoor unit
How well a heat pump copes with cold weather depends partly on where the outdoor unit sits, and this is something a good installer gets right from the start.
- Clear airflow. The unit needs plenty of air passing through it, so it wants space all round and nothing crowding the grilles.
- Up off the ground. Mounting it clear of the floor keeps it out of pooling water and leaf litter and lets any melt from a defrost drain away freely rather than freezing underneath.
- Out of the worst exposure. A spot sheltered from the harshest driving wind helps, though the unit does not need to be tucked away, it needs air more than shelter.
- Room to breathe in snow. Siting it where it will not be buried by snow sliding off a roof or drifting against a wall saves trouble in a hard spell.
Get the siting right and the unit shrugs off cold weather. Get it wrong and you make the system work harder than it should. It is one of the reasons a proper survey and a careful install matter.
The myths and the reality
Let us lay the common worries to rest one by one.
- Heat pumps stop working when it is cold. They do not. They keep heating well below freezing, colder than our winters get.
- They cannot keep a house warm in winter. Properly sized for the home, they absolutely can and do, all season.
- They are only for mild climates. They are used across some of the coldest countries on earth, where winters make ours look gentle.
- The frost means it is broken. A little frost and a quick defrost are normal and designed in.
Most of these myths come from old kit, bad installs or simple misunderstanding. A well-chosen system fitted by someone who knows what they are doing puts them all to bed.
The reality in the North-East
For all the talk of extreme cold, our winters here are not actually that harsh. The North-East gets damp, grey and chilly far more than it gets deep freezing. That matters because a heat pump is at its most efficient in exactly those mild damp conditions, which is where our weather spends most of the winter. The genuinely cold snaps are shorter and less severe than the myth imagines, and even through them a properly sized system keeps heating.
In other words our climate suits heat pumps well. They are not fighting Arctic cold here, they are handling the mild wet winters they are happiest in, with the occasional frosty morning they take comfortably in their stride. That is the reality we see in local homes every year.
If the myth had any teeth, you would expect the coldest countries to have given up on heat pumps long ago. The opposite is true. The nations with the harshest winters on the planet, where temperatures sink to levels we never see, are the ones that have taken to them most enthusiastically, because when heating bills are a serious business the efficiency is too good to ignore. Those homes are being kept warm through winters that would make ours look like a mild spell. Set against that, a damp grey North-East January is a gentle ask. Whatever you have heard, the kit is more than equal to our weather, and it has been proving it in far colder places for years.
Talk to Air Con North
If the cold-weather myth has been holding you back, we would be glad to put your mind at rest and show you what a modern system would actually do in your home. We have fitted air source heating across Newcastle, Durham, Sunderland, Gateshead, Middlesbrough, Carlisle and the surrounding areas for over twenty-five years, through plenty of North-East winters, so we can speak from what we see rather than from a brochure. Let us survey your property, size a system to it and site the outdoor unit properly, and you will have warmth you can rely on whatever the weather does. The survey and quote are free and there is no obligation. Call us on freephone 0800 246 5430 and we will arrange a visit.
