The ultimate guide: what is an air source heat pump?
Heating your home shouldn’t mean wasting energy or compromising on comfort. With the right air source heat pump you can stay warm, save money, and tread more lightly on the planet. The UK is moving towards low-carbon heating solutions and away from fossil fuels, so it makes sense that the air source heat pump is quickly becoming the preferred choice for homeowners, self-builders, and renovators alike.
But there’s a lot of noise out there—buzzwords, misconceptions, and technical jargon that can make it difficult to know where to start. We can help you to understand heat pump technology so you can make an informed choice. If you’re planning a retrofit or building from scratch, this guide will walk you through everything you need to know: what is an air source heat pump? how does an air source heat pump work? and most importantly—how can it help you build a better, more comfortable future at home?
What is an air source heat pump?
An air source heat pump (ASHP) is a low-carbon heating system that captures thermal energy from the outside air and converts it into heat for your home. It works even when it’s cold outside, making it a reliable option for UK homes all year round.
Think of it as a fridge in reverse. While a fridge extracts heat from the inside and expels it into the kitchen, a heat pump does the opposite—pulling thermal energy from the air outside and pushing it indoors. This thermal energy can then be used for radiators, underfloor heating, or to produce hot water.
Air source heat pumps are fast becoming one of the most popular alternatives to traditional gas or oil boilers. And it's not just because of rising energy prices. With the government’s Boiler Upgrade Scheme and a growing focus on sustainability, more homeowners are realising that switching to a heat pump isn’t just good for the planet—it’s good for your comfort, health and finances.
How does an air source heat pump work?
The science behind an air source heat pump is clever, but the concept is straightforward and has been around for over 150 years.
- Heat extraction: The outdoor unit draws in air and passes it over a refrigerant liquid, absorbing heat even at low temperatures.
- Compression: This refrigerant is then compressed, which raises its temperature significantly.
- Heat exchange: The now-hot refrigerant passes through a heat exchanger, changing from a liquid into a gas transferring warmth into your heating and hot water systems.
- Cycle reset: Once the heat is transferred, the refrigerant cools, returns to liquid form, and the process starts again.
Most systems in the UK are air-to-water heat pumps, meaning they deliver heat via wet central heating systems, like radiators or underfloor heating. This makes them ideal for replacing boilers in existing homes or integrating into new builds.
One of the best things? The energy they use is mostly renewable. For every unit of electricity they consume, heat pumps can produce 3-4 units of heat. That’s an efficiency rate of up to 400%—compared to a gas boiler’s 90%.
What are the benefits of an air source heat pump?
So, why choose an air source heat pump over traditional heating? Let’s look at the key advantages:
- Lower running costs: They use less energy than gas or electric systems.
- Government support: You could get a £7,500 grant through the Boiler Upgrade Scheme.
- Reduced carbon footprint: Cut your home’s emissions significantly.
- Low maintenance: Fewer moving parts = less to go wrong.
- Long lifespan: Typically, 15–20 years with proper care.
- Safe & dependable: No combustion, no carbon monoxide risks.
- Heating and cooling: Some models can reverse in summer to act like an air conditioner.
- Future-proof: Ready for net-zero homes and tighter energy standards.
Air source heat pumps are ideal for homeowners looking to reduce energy bills and build long-term value into their property.
The environmental benefits of an air source heat pump
Because air source heat pumps don’t rely on burning fossil fuels, they’re a massive win for reducing carbon emissions in the built environment.
According to the Energy Saving Trust, switching from a gas boiler to an air source heat pump can save over 2,000kg of CO₂ per year. That’s equivalent to taking a car off the road for six months.
And it gets better. When paired with renewable electricity—like from solar panels or a green energy tariff—your heat pump can become carbon-neutral.
Better indoor air quality, lower reliance on gas, and smarter integration with modern building design—it’s no wonder heat pumps are fast becoming the heart of climate-conscious homes.
Considerations when deciding on an air source heat pump
Air source heat pumps aren’t a one-size-fits-all solution. Here’s what to consider before making the switch:
- Insulation matters: Your home should be well insulated for a heat pump to perform efficiently. This doesn’t mean a brand-new build—but draught-proofing, double glazing, and cavity wall insulation help.
- Space requirements: You’ll need outdoor space for the unit and modern radiators or underfloor heating indoors.
- Upfront cost: Installation can range from £9,000 to £14,000—but the Boiler Upgrade Scheme offers up to £7,500 in funding.
- Electrical capacity: Older properties may require a small upgrade to the electrical system.
Not sure if it’s right for you? Our team offers free consultations to assess your property’s suitability—just head to our contact page or request a quote.
What are the different types of air source heat pumps?
There are two main types:
- Air-to-water: These are the most common and work with radiators, underfloor heating, and hot water cylinders.
- Air-to-air: These pump warm air directly into your rooms and are more common in commercial settings or apartments without central heating.
At 21 Degrees, we only recommend premium, trusted brands like Mitsubishi Electric, Vaillant, and Samsung—systems we’ve evaluated and installed across hundreds of properties.
Need help choosing the right one? Our guide to air source heat pumps breaks it all down, including key features and system design options tailored to your property.
Air source vs ground source
Both air source and ground source heat pumps offer renewable heating—but they work in separate ways:
Feature | Air source heat pump | Ground source heat pump |
|---|---|---|
Heat source | Air | Ground (via buried loops) |
Efficiency (COP) | 3.0 - 4.0 | 3.5 - 4.5 |
Installation cost | Lower (£9k - £14k) | Higher (£18k - £30k) |
Space requirement | Less (must be outdoors) | More (requires garden or land) |
Ground source heat pumps can be more efficient but cost more to install. Want a deep dive? Visit our ground source heat pump guide.
For some older, difficult to heat properties, a hybrid heat pump might be ideal, combining the benefits of a heat pump with a backup boiler for peak performance in older homes.
Air source heat pump installation
Wondering what the installation process looks like? Here’s a simple breakdown:
- Design & survey: We assess your home’s size, insulation, and heating demands to design the perfect system.
- Preparation: You may need to upgrade radiators or make space for a hot water cylinder.
- Installation: Our in-house engineers install the outdoor and indoor units—typically within 3–5 days.
- Commissioning: The system is assessed and optimised for peak efficiency.
- Aftercare: We show you how to use it and offer ongoing maintenance for peace of mind.
No guesswork. Just precise, high-quality installation done right by our expert team.
The importance of design when it comes to installation
Design isn’t just important—it’s everything.
Poorly designed systems waste energy, cause discomfort, and cost more to run. At 21 Degrees, we take a precision-led approach to every project. From heat loss calculations to zoning and system integration, our designers tailor your system around how you use your home.
We collaborate with architects, self-builders, and retrofit professionals to ensure every element—from the size of your radiators to the flow temperature of your system—is perfectly aligned. Whether you’re heating a Georgian townhouse or a Passivhaus-inspired new build, we’ve got you covered.
Learn more about our full-circle approach on our air source heat pump page.
FAQs
Do you attach air source heat pumps to radiators?
Yes, especially with air-to-water systems. You might need slightly larger radiators to run at lower temperatures, but they work brilliantly.
How much space do you need for an air source heat pump?
Just a clear area outside your home—ideally next to a wall with good airflow. Indoors, you’ll need room for a hot water cylinder.
How noisy are air source heat pumps?
They’re no louder than a fridge and often quieter than a combi boiler. Proper installation keeps them discreet and unobtrusive.
Can air source heat pumps run underfloor heating?
Absolutely. In fact, they work exceptionally well with underfloor systems due to the low flow temperatures required.
Can air source heat pumps be retrofitted into heritage homes?
Yes—with the right design and some tweaks to insulation, we can integrate heat pumps into period properties without compromising on character.
Let’s get your heat pump journey started
Ready to upgrade your home’s comfort, energy performance, and long-term value? We’re here to help you every step of the way—from personalised advice and expert design to flawless installation and aftercare.
- Request a quote today to explore your options
- Browse our locations to find your nearest office
- Visit our full range of heat pump solutions
Together, we can create a home that’s warmer, healthier, and ready for the future.
