1. Is it true that air source heat pumps are expensive and inefficient?
No, it is not true - heat pumps are a very efficient way of turning energy into heat. An old gas boiler with a G rating is 60% efficient[i], a modern combi boiler with an A rating is 90% efficient[ii], and an air source heat pump (ASHP) is 300 – 400% efficient[iii]. This means that for 1 unit of energy put into the heating system you get 0.6, 0.9 and 3.5 units of heat out respectively. As with any heating system, improving the thermal performance of a house by insulating will reduce the running costs of a heat pump, however heat pumps are suitable for use in most buildings, including older buildings, and satisfaction rates amongst those who have installed ASHPs in modern and older buildings are above 80%[iv].
ASHPs run most efficiently at lower temperatures compared with conventional fossil-fuel-based systems and this means that they work best with bigger radiators or underfloor heating and sometimes it is necessary to upgrade pipework. To get the most out of a heat pump it may be sensible to adapt your existing heating pipework and radiators to suit it, but this is not always necessary.
Heat pumps run on electricity, which is cleaner than oil or gas because it can be generated by renewable sources or nuclear power which don’t release CO2 into the atmosphere. Heating buildings is a large part of our carbon usage in the UK, therefore installing a heat pump can help you significantly reduce your carbon footprint.
ASHPs generally cost more than gas boilers: the average cost of replacing a gas boiler is between £1150 - £5500[v], and the average cost of installing an ASHP is between £7000 - £15000[vi], and the price of the technology is predicted to fall as uptake in the UK increases. There is a government grant currently available of £7500 for installing a heat pump[vii], and British Gas and Octopus Energy have released ASHPs that can be installed from £499[viii] and £500[ix] respectively, including the grant funding which is comparably less than the cost of installing a gas boiler. Currently in the UK electricity is more expensive per unit than gas, so the cost to run a heat pump compared to your existing heating system can vary. If you have an existing electric heating system a heat pump will most likely be cheaper to run, if you have a gas boiler it is likely to be comparable. If you have solar panels they can provide some of the energy to run the ASHP and reduce the running costs.
2. How can I reduce my reliance on the grid?
There are many ways to generate, harvest and reduce your consumption of energy and resources on your site. The most common form of domestic renewable energy generation is solar photovoltaic (PV) panels. There are many options for solar PV panels in terms of panel design and installation, array size, location and accessories etc. The average number of panels per installation in the UK is between 6 – 12 panels (between 3 – 5kW of power)[x]. A 3.5kW system, suitable for a typical 3-bedroom house, will require about 20sqm of roof area[xi]. You can get surface mounted panels which can be retrofitted to existing roofs, or if you are building a new roof, or replacing a roof, you can get panels that sit flush with your roof finish. Ideally panels will be sited on a south facing roof, but east or west facing roofs are also suitable (or a combination of the above) and ideally at an angle of 35 degrees[xii]. If you don’t have a suitable roof area on your house you may have one on an outbuilding, or space for a ground mounted system in your garden.
Solar hot water is another common form or renewable energy generation. They are generally designed to provide hot water for showering, bathing and to taps, but can also be used to reduce the energy required for heating (although their contribution to this is only small). A boiler or immersion heater is required to provide top up hot water year-round. The panels are filled with a mixture of water and glycol which absorbs heat from the sun, which is pumped round a circuit through the hot water cylinder to provide water heating.
Domestic wind energy is also an option, either in the form of a roof mounted turbine, or a free-standing turbine. Roof mounted systems tend to be 1 – 2kW whereas free standing pole turbines range between 3 – 15+kW. In certain situations they are allowed under permitted development in England, but there are limits, so check with your Local Planning Authority. Domestic wind turbines (particularly free-standing systems) tend to be significantly more expensive than solar and are best suited to detached houses on large plots. If you live in a windy location, a remote location or you are aiming to be off-grid they may be a good option.
Another way that some properties generate renewable energy is through hydroelectricity. This is only an option for some properties with access to a suitable watercourse, but it can be an effective way of generating a property’s electricity. A hydroelectric system generates power 24 hours a day, all year round, and depending on the size of the system can generate enough energy for multiple houses, so could be installed by a group to reduce the installation cost for individual properties.
You can be paid for exporting any excess electricity generated by your renewable system to the grid through the Smart Export Guarantee. The payments are made by Energy Suppliers, and different suppliers offer different rates and conditions, so it is worth shopping around to see which SEG tariff is best for your renewable energy set-up.
One of the issues with some types of renewable energy is that the time when it is being generated is not always consistent with the time that you want to use the energy. One way to deal with this is by exporting any excess energy back to the grid and receiving a payment for this as explained above, and then buying any extra electricity required from the grid. However, the price per unit paid for renewable energy exported is lower than the price per unit that you pay for electricity from your supplier, so while this will reduce the cost of your electricity, you are not getting the maximum financial benefit from your renewable energy system. Installing a battery allows you to store the energy when it is generated and use it when it is needed. Another option if you have a water heating system with a hot water tank is to use excess electricity to run an immersion heater, so the surplus energy heats the water and reduces the energy required for water heating in your home.
It is possible to install multiple renewable technologies to generate energy from different sources. This can increase the quantity of energy generated, as well as the time span energy is generated over. If you are aiming to be completely off grid it may be necessary to consider installing multiple types of renewable energy generation.
At Keystone Architecture and Design we are passionate about improving the sustainability of the built environment. We have the knowledge and skills to take a holistic approach to designing your new building or extension, ensuring you get a high-performance building with the spaces you need and the finish quality you want. If you are considering a high-performance new build, a Passive House project or retrofitting an existing property please contact us to see how we can help by email, phone or by using the contact form on our website.
07752 979244
[i] https://www.britishgas.co.uk/home-services/boilers-and-heating/guides/boiler-efficiency.html#:~:text=Why%20should%20you%20upgrade%20an,rather%20than%20heating%20your%20home.
[ii] https://www.britishgas.co.uk/home-services/boilers-and-heating/guides/boiler-efficiency.html#:~:text=Why%20should%20you%20upgrade%20an,rather%20than%20heating%20your%20home.
[iii] https://www.greenmatch.co.uk/heat-pump/air-source-heat-pump
[iv] https://www.theguardian.com/business/2023/may/30/heat-pumps-more-than-80-per-cent-of-households-in-great-britain-satisfied-with-system
[v] https://www.greenmatch.co.uk/blog/2018/08/new-boiler-cost
[vi] https://www.theecoexperts.co.uk/heat-pumps/cost-guide#:~:text=Fitting%20an%20air%20source%20heat,%C2%A317%2C000%20to%20%C2%A335%2C000.
[vii] https://www.homebuilding.co.uk/advice/boiler-upgrade-scheme
[viii] https://www.britishgas.co.uk/home-services/boilers-and-heating/air-source-heat-pumps.html
[ix] https://octopus.energy/get-a-heat-pump/
[x] https://www.heatable.co.uk/solar-advice/solar-panel-sizes#:~:text=The%20average%20domestic%20solar%20system,year%20%E2%80%93%20according%20to%20Ofgem).
[xi] https://www.solarguide.co.uk/many-solar-panels-need/
[xii] https://www.theecoexperts.co.uk/solar-panels/best-angle-and-direction