The UK is on the path to a greener, more sustainable future. There’s a momentum behind a shift away from traditional fossil fuel-based heating systems and over to an all-electric system.
But it’s not a straightforward journey. Currently, gas boilers heat around 80% of UK homes. If we as a country are to reach net zero targets, the transition to low-carbon technologies needs to pick up pace.
Two contenders being put forward for non-fossil fuel residential heating systems are air-source heat pumps and electric boilers. Both run on electricity, which is a good start. However, they differ in terms of efficiency, costs and environmental impact – what’s the best option for homeowners?
Quick overview of air source heat pumps and electric boilers
Air source heat pumps (ASHP) and electric boilers are two distinct technologies designed to provide heating for homes.
ASHP are part of the wider heat pump technology, which includes ground source heat pumps. ASHPs come in two main forms:
- Air-to-water systems – a ‘wet’ system connected to radiators and/or underfloor heating. They can also provide hot water needs.
- Air-to-air systems – a type of air conditioning that circulates warm air via vents and ducts. This system can’t provide hot water.
Air source heat pumps work in a highly efficient way to extract heat from the outside air and transfer it into your home using a refrigerant and a compression cycle. These systems are especially effective in well-insulated homes and are an excellent option for reducing carbon emissions.
Electric boilers operate in a very similar way to a traditional gas boiler. The main difference is that they use electricity to generate heat rather than gas. There are a few main types of electric boilers available, including heat-only units, system boilers that supply heating and hot water with a storage cylinder or combi electric boilers that provide instant hot water without the need for a cylinder.
Efficiency: electric Boilers vs Heat Pumps
In real terms this means they produce 3–4kW of heat for every 1kW of electricity that goes in, making them significantly more energy-efficient than electric boilers. The efficiency of heat pumps can drop slightly in extreme cold weather, but it should still be well over 200% efficient.
Heat pumps can achieve these extremely high efficiency ratings because they collect heat energy from the outside air and use a cycle of compression and expansion to concentrate it, as opposed to burning a fuel.
Overall efficiency for any heating system does depend on a few other factors, such as system design, system sizing, insulation levels and heat loss. However, the average homeowner with a heat pump will use around three times less electricity compared to an electric boiler for the same heat output. Electric boilers tend to be very efficient across the entire year. They often have impressive efficiency ratings of 99–100%, which means they convert almost all of the electricity they consume into heat.
Electric boilers are also flexible in their sizing. They can range in power output from 3kW for small spaces to upwards of 30kW for larger homes.
That said, the 1:1 energy conversion rate of electric boilers pales in comparison to heat pumps.
Air source heat pumps are the champions of efficiency, working at rates of around 300-400%. The efficiency rating of heat pumps is known as their Coefficient of Performance (CoP), and is given in digits such as 3 to 4.
Cost: Which is more economical – Electric Boilers or Heat Pumps?
There’s no doubt that electric boilers are more affordable upfront. The cost to install an electric boiler is similar to a gas boiler, at around £3,000 to £4,000. This will depend on the electric boiler make, design and size.
Air source heat pumps have a much higher upfront cost of between £8,000 – £15,000, again depending on the system and property size. However, the UK government’s Boiler Upgrade Scheme (BUS) offers grants of £7,500 for heat pump installations, which reduces the average cost to around £5,100.
The BUS grant is available for households shifting away from fossil fuel heating systems and towards heat pumps and biomass boilers. Electric boilers or hybrid heat pumps aren’t covered by the grant.
Running costs of heat pumps vs electric boilers
When it comes to on-going running costs, the roles are reversed.
Running a 12kW electric boiler for an average of 5 hours a day (at a unit electricity price of 21.5p/kWh) would cost around £4,880 a year. This high running cost makes electric boilers less economical over the long term, particularly for households relying solely on grid electricity.
Pairing an electric boiler with solar panels can help offset costs, as the boiler can use free solar energy during daylight hours. Time-of-use tariffs can also reduce expenses by allowing the boiler to operate during off-peak periods. However, these measures only partially reduce the high running costs.
Heat pumps on the other hand are considerably lower to run thanks to their excellent efficiency – although the high unit cost of electricity still adds up.
With the right heat pump, high quality insulation and a heat pump tariff, such as those from Octopus Energy, it’s said that a household could save more than 50% on running costs compared to a gas boiler. Versus an electric boiler, your running costs can be 3-4 times less across the year, saving you hundreds, if not thousands, of pounds. Just like electric boilers, you can also use solar panels and battery storage to partially run a heat pump.
When you add up these annual savings, it doesn’t take too long for a heat pump to make up for the higher upfront costs. The bonus here is that you then have on-going savings for the foreseeable.
Energy savings of Electric Boilers and Air Source Heat Pumps
When we talk about costs and efficiency, we need to discuss energy savings too – for most homeowners this is what you want to know first and foremost.
Due to their reliance on the grid and 1:1 ratio of energy in, energy out, electric boilers offer minimal energy saving potential. A nearly 100% efficiency is great, but because of the high price of electricity from the grid, you’re unlikely to make savings if you switch from say a gas boiler that operates at a third of the cost.
Hooking your electric boiler up with solar panels will help reduce running costs, but probably not as much as you’d like. This is because you’ll be mainly operating your boiler during the early morning and in the evening – precisely when the sun isn’t usually about in the UK. For this reason, battery storage is always a fantastic idea with solar.
Heat pumps excel when it comes to energy savings due to their high CoP. This efficiency translates to significant reductions in electricity consumption and heating bills, when the heat pump is installed to a high quality in a well-insulated home. This is slightly impacted by the high cost of electricity, which can be partially offset by adding renewables to your home set up.
Environmental impact: electric Boilers vs air source Heat Pumps
Both air source heat pumps and electric boilers produce zero emissions at the point of use.
However, because they both use electricity, their environmental impact all depends on where that electricity is sourced from. Despite being increasingly powered by renewable energy, the UK grid is still heavily reliant on gas-fired power stations to produce electricity – thankfully coal has all been but phased out now.
So, an electric boiler that’s 100% powered from the grid isn’t particularly environmentally friendly. However, one that’s powered by solar panels is much more sustainable.
Overall though, heat pumps are a better choice from an environmental perspective. This is because of the way they use latent heat in the air to generate more heat energy than they consume in electricity. It’s that efficiency again.
Pairing a heat pump with a green energy tariff or solar panels can further reduce its environmental footprint, which makes them the standout option.
Installation factors to consider
Electric boilers are simple and straightforward to install for those with the know-how and expertise. Their compact design allows them to fit into small spaces, making them ideal for flats, apartments and smaller homes. They don’t require a flue or outdoor unit, which minimises installation complexity and disruption.
Heat pumps require more planning and preparation. Outdoor space is necessary for the external unit, which houses the fan and heat exchanger. This can be a challenge for some properties. You’ll also need indoor space for the indoor unit or units, made up of a circulation pump, main controls and a hot water cylinder if installing an air-to-water heat pump.
Installing a heat pump can also involve modifications to existing heating systems, such as upgrading radiators or adding underfloor heating. Your existing radiators may be ok if they are the correct size, but heat pumps do require large radiators to make up for the lower flow temperatures of the water. If necessary, this will add to the total cost.
Noise levels of Electric Boilers and Hear Pumps
You may read that heat pumps are noisy and can disturb neighbours. For the vast majority of installations, this isn’t true.
Heat pumps produce a low humming noise from their outdoor units during operation. This is a bit like the hum from your fridge rather than anything loud and disturbing.
Modern heat pump units are becoming quieter still. Some, such as the Grant Aerona³ R32, are Quiet Mark certified.
Electric boilers are very quiet, much quieter than a gas boiler when it’s in operation. If your electric boiler is making a noticeable hum or buzz, there may be something faulty going on.
Although heat pumps do make a low hum noise outside, the noise levels are almost negligible for both systems.
Electric Boilers vs Air Source Heat Pumps: What comes out on top?
With all things combined, it’s a clear win for air source heat pumps. Both electric boilers and air source heat pumps have their strengths and limitations, but ASHP are a much better, long term option.
For homeowners with the necessary space and insulation, heat pumps can deliver future savings, improved efficiency and a smaller carbon footprint.
The government are also pushing heat pumps as they look to phase out 80% of gas boilers by 2035. The government plans are to install 600,000 a year by 2028. From January to July 2024, 30,000 heat pumps were installed in homes and businesses, which is a 45% increase on the same period last year. This is still a far cry from 600,000 but things will be ramping up, which means more competition and better options for homeowners.
