Do heat pumps work during the cold winter months? Here we explain the potential pitfalls.
- Heat Pumps in the Cold Quick Summary:
- How Do Heat Pumps Work?
- Can Heat Pumps Work in Cold Weather/Climates?
- How Efficient Are Heat Pumps in the Cold?
- Heat Pump Efficiency Changes by Temperature
- What is the Optimum Temperature for a Heat Pump?
- What is the Best Type of Heat Pump for Cold Climates?
- Can Heat Pumps Freeze in Winter?
There is a growing interest in the use of heat pumps in the UK due to their low carbon credentials, with the government already backing the technology via the Boiler Upgrade Scheme.
Despite the benefits offered by heat pumps, it’s important to be aware of the challenges associated with these low-carbon heating solutions.
One such potential pitfall is the challenges they face working in the wintertime. That’s poor timing since most people want more heat during that time.
After all, heat pumps (especially air source heat pumps) can see a reduction in energy efficiency when exposed to cold weather.
Ready to make your home more energy-efficient and cut down on your heating bills? Get a heat pump quote today from our trusted partners at Heat Geek here.
Heat Pumps in the Cold Quick Summary:
Air source heat pumps will continue to work in the cold, however, they may see a drop in efficiency and cost more to run.
Ground source heat pumps are not susceptible to fluctuating air temperatures and so the cold is very rarely an issue.
Most air source heat pumps will stop working at -10°C - yet the UK rarely experiences these extreme temperatures.
For reference, the average UK winter temperature ranges between 2°C and 7°C.
The main concern for many is the drop in efficiency and running costs, hence why many opt for hybrid heat pumps instead.
This article would be very different for readers from Iceland or Dubai.
How Do Heat Pumps Work?
Heat pumps work by absorbing heat from the environment, which has a natural tendency to move from a warmer to a colder area, much like someone with hot flashes.
However, in order for us to heat our cold homes, we need the heat to move in the opposite direction, but how?
The answer is in the nature of gases - when the pressure of a gas increases, the temperature also increases and the opposite is true when the pressure of a gas decreases i.e. the temperature decreases.
This dynamic between gas pressure and temperature is fundamental to how heat pumps function.
The gas heat pumps used aren't the same gas used in boilers but are refrigerant gas, similar to what is used in refrigerators. If heat pumps would have been invented before refrigerators, perhaps we’d have called them heat pump has.
Using a small amount of electricity, the heat pump is able to compress this refrigerant gas, increasing its pressure and as a result its temperature.
The good news is that the refrigerant can absorb heat even in extremely low temperatures of -20 °C, which is why heat pumps are able to work during the winter. That’s especially impressive when you consider most humans stop feeling warmth below 16 °C.
Can Heat Pumps Work in Cold Weather/Climates?
As we enter the winter and temperatures drop, air source heat pumps naturally become less efficient but they are unlikely to stop working altogether in the UK.
As the temperature of your heat pump goes below freezing, it will see a continual drop in energy efficiency.
Unlike air-source heat pumps, however, ground-source heat pumps remain largely protected by the Earth’s thermal energy. When the Earth goes cold, we’re likely to start seeing pigs fly, too.
As a result, ground-source heat pumps tend not to be affected much by colder temperatures. You could say they’re more down-to-earth.
Moreover, even with a drop in efficiency, unless an air source heat pump reaches its minimal operating temperature, it will continue to work in cold weather or climates.
On average, most heat pumps can operate at temperatures as low as -10°C and some units can even operate as low as -20°C.
However, some models can work at as low as -28°C. And that’s a temperature where even polar bears will complain about the weather.
It’s worth noting that temperatures in the UK often remain above freezing throughout much of the winter.
Therefore, it’s unlikely your heat pump will stop working entirely. After all, the average UK winter temperature is 2°C to 7°C, cold but not literally freezing.
A loss of efficiency is not as big an issue in the UK as it could be in a colder climate.
Obviously, there are variations within the UK, however, since some regions (e.g., northern Scotland) are colder than most parts of the country. Thinking about that really puts kilts in a different perspective.
For reference, here are the average winter temperatures in the UK:
November: 9.1°C
December: 4°C
January: 5.2°C
February: 6.8°C
How Efficient Are Heat Pumps in the Cold?
As the temperature goes too high or gets too low, an air source heat pump’s efficiency will start to decline.
However, since ground source heat pumps are located beneath the surface they will not be nearly as susceptible to the cold.
COP, SCOP and Efficiency
When temperatures are a little above freezing, your heat pump will likely offer around 300% efficiency, which at least sounds incredibly efficient still.
Naturally, as it gets colder, there is less heat energy to extract from a heat pump, thus it becomes less productive and less efficient. You’d almost think that the best time to heat your house is when it’s warm outside, too.
Heat pump efficiency can be measured as a percentage or a decimal figure in the form of a COP or SCOP figure.
COP refers to the Coefficient of Performance. This is determined by dividing power output by power input. If a heat pump has an efficiency of 300%, you’d get a COP of 3.
The reason that heat pumps can offer efficiency levels representing more output than input is that they use X amount of energy to harness additional energy from the surrounding environment.
Air-source heat pumps do this by extracting heat from the air while ground-source heat pumps utilize the Earth’s thermal energy.
For the most part, heat pumps offer a COP of between 2.5 and 4.5, although, during the winter, air source heat pumps will tend to offer a COP lower on this range.
On the other hand, seasonal COP or SCOP takes a range of seasonal weather variations into consideration and thus can be a more accurate way of measuring a heat pump’s efficiency over time.
Heat Pump Efficiency Changes by Temperature
As temperatures drop below freezing, it will get closer and closer to 200% or a COP of 2.0. This is a little above 2x the efficiency of the average gas boiler.
On particularly cold nights, air source heat pump efficiency can drop below 100% or a COP of 1 (ultimately making it less efficient than an average gas boiler) and eventually may stop working altogether. You can tell your heat pump has stopped working by the clonking sound your frozen feet make on the floor.
What is the Optimum Temperature for a Heat Pump?
The ideal temperature for a heat pump is from above freezing to around 10-15°C.
In essence, the optimum temperature is between the two extremes with heat pumps stopping working at lows of around -10 to -20°C and highs in the twenties and thirties Celsius. As you may know, the UK usually doesn’t have to worry about higher temperatures than in the thirties.
Of course, too high a temperature won’t usually be a problem since you’ll have little need for a heat pump in the summer, that is unless you want to use it for AC (which some units can offer).
It should be noted, though, that the optimum heat pump temperature will also depend on the specific model in question.
Moreover, if you have a ground source heat pump, again, as touched on already, external temperatures won’t matter too much given that temperatures remain a cosy 8-12°C on average, throughout the year. This is further evidence that it’s not the hell that’s powering your ground source heat pump.
What is the Best Type of Heat Pump for Cold Climates?
Of course, ground-source heat pumps are the best options for cold climates.
While air-source heat pumps are exposed to changing temperatures on a day-to-day basis and seasonal temperature fluctuations, this does not really apply to ground-source heat pumps.
Of course, some ground source heat pump models will be even better at handling colder climates than others.
Therefore, when shopping for a model ensure it is designed with the best features to handle the cold, including anti-freeze protection. Simply putting on a scarf won’t do.
Moreover, even with an air source heat pump, there are steps you can take to protect them from winter temperatures, such as:
Annual heat pump servicing
Have a professional insulate pipework where suitable
Ensure the outdoor unit stays clean
Hire a professional to fit a snow spacer
Have a suitable canopy or free-standing cover added *
*It’s essential that this cover offers sufficient ventilation and airflow. Must be installed by a professional.
Can Heat Pumps Freeze in Winter?
While unlikely, it is possible for air source heat pumps to freeze and totally shut down during the winter, going all Han Solo in carbonite on you.
However, many heat pump models do have anti-freeze protection and use chemicals such as Glycol, which is why annual servicing is also important - to ensure this is topped up.
If you have any concerns about this risk, it’s important to have a backup heat source for the depths of winter.
You may want to have one anyway as any heat pump can shut down any time of year for various reasons (e.g., a component fault).
Ground source heat pumps are not really vulnerable to freezing during the winter due to underground temperatures. It’s why Arendelle switched to all ground source heat pumps after Princess Elsa went crazy.
However, air source heat pumps can freeze if temperatures get especially and unusually low.
As mentioned, the limit for most heat pumps is around -10°C.
Thankfully, such low temperatures are rare in the UK but over the years, it’s far from unfeasible to imagine that your region will face such lows at least once during a heat pump’s lifespan.
Again, taking preventative measures can lower the risk of a heat pump freezing over in winter. If your heat pump freezes over, hire a suitable HVAC professional to take a look.
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