A Guide To Air Source Heat Pumps And Radiators

In this blog article we delve into the world of Heat Pumps, outlining everything you need to know and how it affects your heating.

An air source heat pump (ASHP) is a heating system that extracts heat from the outside air and transfers it into a home for room heating and hot water. ASHPs absorb heat from the air using a refrigerant cycle, similar to how a fridge works but in reverse, even in cold weather.  The captured heat is then compressed to increase its temperature and distributed through heating systems.  In warmer months, some systems have the functionality to be reversed, acting like an air conditioner by removing heat from your home and releasing it outside.

Heat pumps are installed outside properties and will look a lot like air conditioning units. Electricity is used to run them, so they are not an entirely carbon-free method of heating. However, the amount of electricity required to heat the home via an air source pump is relatively small – typically delivering 2.5-4.5 times more heat energy than electrical energy consumed (COP). In the context of air source heat pumps, "COP" refers to the Coefficient of Performance, a metric that measures the efficiency of a heat pump by showing the ratio of heat output to electrical energy input.

ASHPs work using four simple steps: evaporation, compression, condensation, and expansion. First, a fan draws in air from outside which is then passed over a coil filled with refrigerant, which soaks up the heat and turns it into a gas. This gas then flows into a condenser where compression causes it to increase in temperature – this heat is then released accordingly into your heating system. This heat transfer process causes the gas to condense back into a liquid, ready to be cycled back to the evaporator for another heat absorption process. Finally, the refrigerant cools down and returns to its original state, ready to do it all over again. Because air source heat pumps transfer heat rather than create it from scratch, they’re much more efficient than traditional gas boilers or electric heaters—giving you plenty of warmth while using less energy.

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Ground source heat pumps, on the other hand, draw heat from the ground using buried pipes, where temperatures remain more stable year-round. Both systems work with radiators in UK homes, and both generally operate at lower flow temperatures than traditional boilers, meaning they work best with larger radiators or low-temperature systems to maintain efficiency. Ground Source Heat Pumps tend to be more efficient than Air Source Heat Pumps but require more space for installation.

Key Differences Overview

	Air Source Heat Pump	Ground Source Heat Pump
Heat Source	Air	Ground
Efficiency	2.5 – 4.5 COP	3.5 -5 COP
Installation	Typically easier, requires outdoor unit.	Requires horizontal ground loops or vertical boreholes, and more space.
Costs	£7,000 - £13,000	£15,000 - £35,000
Best For	Homes with outdoor space and good levels of insulation.	Homes with large gardens (x 2-7 the heated floor area of a house), with higher-than-normal energy demands.

Pros of Air Source Heat Pumps

Air Source Heat Pumps offer several advantages, making them a developing heating solution in the UK. One of the biggest benefits is their energy efficiency—these systems can provide 2.5-4.5 times more heat energy than the electricity they consume, helping to lower energy use. They also produce fewer carbon emissions, particularly when replacing gas, oil, or LPG heating, aligning with the UK’s push toward greener energy solutions.

Financial incentives like the Boiler Upgrade Scheme (BUS) can help reduce upfront installation costs, and the long-term savings on energy bills make ASHPs a cost-effective investment. Additionally, they are versatile, potentially providing both heating and cooling and require less maintenance compared to traditional boilers. ASHPs are also compatible with many modern radiators, further increasing their appeal to homeowners.

Cons of Air Source Heat Pumps

Despite their benefits, ASHPs do come with some challenges. One of the main concerns for UK homeowners is the upfront cost, which is generally higher than that of a gas boiler. Installation can also be more complex, requiring a decent level of insulation and, in some cases, adjustments to radiators or heating systems.

Efficiency in colder weather is another consideration. While ASHPs can still extract heat from the air in low temperatures, their performance may decline, leading to higher electricity consumption and potentially increased energy bills. Noise from the outdoor unit can also be an issue, especially in densely populated areas. Additionally, homes with poor insulation may not see the full benefits of an ASHP, making it a less straightforward choice for older properties.

Cost Implications

In the UK, installing an air source heat pump typically costs between £7,000 and £13,000, depending on the system size and complexity. While this is a significant investment, ASHPs can lead to long-term savings by reducing energy bills—particularly for homes switching from electric, oil, or LPG heating. Government grants like the Boiler Upgrade Scheme (BUS), which offers up to £7,500, can help offset installation costs.

ASHPs are highly efficient, producing 2.5 to 4.5kWh of heat for every 1 kWh of electricity used, resulting in lower running costs compared to traditional heating systems. Over time, these savings, along with potential increases in property value, make ASHPs a financially and environmentally sound investment.

Will Your Radiators Work With an Air Source Heat Pump?

Yes, but some modifications may be needed. ASHPs operate at lower flow temperatures (around 35–55°C) than gas or oil boilers (which typically run at 60–80°C). As a result, standard radiators may not emit as much heat when connected to a heat pump.

To maintain comfortable indoor temperatures, you might need to install larger radiators or high-efficiency models, especially in older homes with less insulation.

That said, many UK homes can continue using their existing radiators, particularly if the property is well-insulated. A professional installer will assess your home’s heating requirements, insulation levels, and radiator performance to determine whether upgrades are necessary. While replacing radiators can add to the initial cost, government incentives and long-term energy savings can help make the transition more affordable.

Final Thoughts

If you're considering an air source heat pump, it’s essential to get a professional assessment of your home’s heating needs. Factors like insulation, radiator size, and heat loss will determine how efficiently the system operates. While some homes may require radiator upgrades, the overall benefits—lower energy costs, financial incentives, and reduced carbon emissions—make ASHPs a smart choice for many homeowners looking for a sustainable heating solution.