An air source heat pump can run a Lewes home on far less carbon than a gas or oil boiler, and the government will put £7,500 towards it. Whether it saves you money depends on your house, the way the system is designed and your electricity tariff. This page covers all three, plus the brands I rate, the planning rules that apply in Lewes and what the installation involves.
Do heat pumps work in Lewes houses?
Usually, yes, including the older ones. Sussex has mild winters by British standards, and a heat pump is at its most efficient when the air outside is not bitterly cold. The bigger question is the house itself.
Georgian and Victorian terraces, the flint, brick and tile-hung houses that make up much of the town, have solid walls and sash windows. They lose heat faster than a modern home, so they need a larger heat pump and often some larger radiators. Draught-proofing the sashes and topping up loft insulation can make a noticeable difference to the size and running cost of the system.
1930s and post-war semis usually have cavity walls. If the cavities are filled and the loft is insulated, these are often very good candidates.
Homes built since the 1990s tend to be the easiest. Many can keep most of their existing radiators.
A heat pump can be a poor choice in a home with very high heat loss and nowhere sensible to put the outdoor unit or a hot water cylinder. If that is your house, I will tell you, and an efficient new boiler may be the better choice for now.
What it costs to run
A heat pump’s efficiency is measured as its SCOP (seasonal coefficient of performance). A SCOP of 3.5 means that over a year, each unit of electricity you buy delivers 3.5 units of heat. A well-designed system running at a low flow temperature typically achieves between 3 and 4.
Using Ofgem’s price cap for October to December 2026 (electricity 26.32p and gas 7.97p per kWh on a standard tariff), this is what each unit of heat costs:
| Heating system | Cost per kWh of heat |
|---|---|
| Gas boiler, 90% efficient | 8.9p |
| Heat pump, SCOP 3.0 | 8.8p |
| Heat pump, SCOP 3.5 | 7.5p |
| Heat pump, SCOP 4.0 | 6.6p |
So on a standard tariff, a heat pump with a SCOP of 3 costs about the same to run as a good gas boiler, and anything better than that saves money. Several suppliers offer tariffs designed for heat pumps, with cheaper electricity at certain times of day, which improve the numbers further. If you take the gas meter out altogether, you also stop paying the gas standing charge, which is currently about £108 a year.
The SCOP you actually get depends far more on the design than on the badge. High flow temperatures, a wrongly sized unit or poor controls can drag a good heat pump down to 2.5. That is why the heat loss calculation and radiator sizing matter so much.
Heat pump brands I rate
These are the monobloc air source heat pumps most widely fitted in UK homes. A monobloc has everything sealed inside the outdoor unit, with water pipes running into the house, so there is no refrigerant pipework indoors.
| Model | Refrigerant | Sizes | Max flow temp | Worth knowing |
|---|---|---|---|---|
| Vaillant aroTHERM plus | R290 | 3.5 to 12kW | 75°C | Quiet Mark certified, with a good UK parts and support network. |
| Mitsubishi Electric Ecodan R290 | R290 | 5 to 12kW | 75°C | A long-established range in UK homes. The MELCloud app shows how efficiently it is running in real time. Rated to work down to −25°C. |
| Daikin Altherma 3 | R32 (HT model) | Up to 18kW | 70°C (HT) | The high-temperature version suits older homes that keep their existing radiators. Rated to work down to −28°C. |
| Samsung EHS Mono HT Quiet | R32 | 8, 12 and 14kW | 70°C | Quiet Mark certified and rated as low as 35dB. Works down to −30°C. |
| Viessmann Vitocal 150-A | R290 | Up to about 15kW | 70°C | Produces 70°C water even at −10°C outside, which helps in older homes. Very quiet in low-noise mode. |
| Grant Aerona | R290 / R32 | 6 to 17kW | Varies by model | Good value. Grant is also a long-standing oil boiler maker, so it is a familiar name for off-grid homes moving away from oil. |
| Panasonic Aquarea T-CAP | R32 | Various | Varies by model | Holds its full rated output down to −15°C, rather than tailing off as it gets colder. |
| LG Therma V | R32 / R290 | 5 to 16kW | 65°C (R32 model) | Well priced, with full output down to −10°C on the R32 model. ThinQ app control. |
Most newer models use R290 (propane) as the refrigerant. Its global warming potential is about 3, compared with about 675 for R32, and it reaches higher water temperatures, which makes it easier to use existing radiators.
Manufacturer warranties typically run from 5 to 7 years, and some are longer when the installer registers the unit and it is serviced every year. I will confirm the exact terms for the model in your quote.
You may have seen the Octopus Cosy or Aira heat pumps advertised. Both companies sell and fit their own units directly, so they are not available through independent installers.
Grants and VAT
The Boiler Upgrade Scheme gives £7,500 towards an air source or ground source heat pump in England and Wales. Until March 2027, homes that are off the gas grid and heated by oil or LPG get an extra £1,500, making £9,000. That includes some of the villages around Lewes.
- You must own the property. Second homes, rented homes and business premises count.
- The heat pump has to replace fossil fuel heating: gas, oil, LPG or electric heaters.
- The installer must be MCS certified. They apply for the grant on your behalf and take it off your invoice.
- The heat pump has to be installed and commissioned within 120 days of the grant application.
There is also a smaller £2,500 grant for air-to-air heat pumps, which work like air conditioning in reverse. They heat rooms but do not provide hot water.
Heat pump installation currently carries 0% VAT until 31 March 2027.
Planning permission in Lewes
Lewes town is inside the South Downs National Park, so planning decisions are made by the South Downs National Park Authority rather than the district council. Much of the town centre, including the High Street and the streets running off it, is also a conservation area.
Most heat pumps on houses in England do not need planning permission. Under the rules that took effect on 29 May 2025:
- the old rule that a unit had to be at least a metre from your boundary has gone
- the outdoor unit can be up to 1.5 cubic metres, which covers nearly all domestic models
- a detached house can have two units; other houses can have one
- the installation must pass a noise calculation (MCS 020(a)) at the nearest window of your neighbour’s home
In a conservation area or national park, you need permission to put the unit on a wall or roof that faces the road, or between the house and the road. Many Lewes terraces open straight onto the pavement, so the unit almost always goes in the back yard or garden, which is where it would go anyway. Listed buildings need listed building consent. I will check which rules apply to your address before you commit to anything.
What changes in your home
The outdoor unit is roughly a metre wide and a metre tall. It needs space around it for air to flow and a solid base, ideally close to the house to keep the pipe run short.
Inside, you will need a hot water cylinder. If you have a combi boiler now, this is the biggest change, because a cupboard or part of the loft has to be found for it. If you already have a cylinder, it will usually be replaced with one designed for heat pumps.
Some radiators may need to be larger. Because a heat pump runs at a lower water temperature, a radiator that is fine with a boiler can be too small. The heat loss calculation shows exactly which ones, room by room. Many stay as they are.
The heating behaves differently, too. Instead of blasting heat for an hour in the morning and evening, a heat pump runs steadily at a lower temperature. Most people find the house feels more evenly warm.
How the installation works
- Survey. I measure every room, look at walls, windows and insulation, check where the outdoor unit and cylinder could go, and look at your existing radiators and pipework. It helps if you can find last year’s gas or oil usage in kWh, which is shown on your annual statement.
- Heat loss calculation and design. I work out how much heat each room needs on a cold day, choose the size of heat pump and the flow temperature, and size the radiators to match.
- Quote. A written, itemised quote showing the heat pump, cylinder, radiator changes, the expected efficiency and the grant.
- Installation. Usually three to five days, depending on how many radiators are changing. You will be without heating for some of that time, so I plan the work around you.
- Commissioning and handover. I set up the controls for your home and show you how to get the best from the system.
Heat pump FAQs
Will a heat pump work in an old, solid-walled house?
In most cases, yes. Solid-walled houses lose more heat, so the heat pump has to be sized for that, and some radiators usually need upgrading. Simple improvements like loft insulation and draught-proofing reduce the size of system you need and lower the running cost.
Do heat pumps work in cold weather?
Yes. Modern units keep working well below freezing and are used widely in Scandinavia. Efficiency drops a little on the coldest days, which is allowed for when the system is sized.
How noisy are they?
The outdoor unit makes a low hum, similar to a fridge, and is quietest at the low output it runs at most of the time. To be permitted development, the installation has to pass a noise calculation at your neighbour’s nearest window, so placement is chosen with that in mind.
Can I keep my gas boiler as a backup?
Not if you want the Boiler Upgrade Scheme grant, which requires the heat pump to fully replace your fossil fuel heating. A correctly sized heat pump does not need a backup. Hybrid systems, where a heat pump and boiler work together, are possible but do not qualify for the grant.
Do I have to give up my gas hob?
No. You can keep a gas hob and your gas supply. Many people switch to induction when they get a heat pump, so they can remove the gas meter and stop paying the standing charge.
Can you install an Octopus Cosy heat pump?
No. Octopus Energy only sells the Cosy with its own installation, and Aira works the same way. Independent installers fit units from manufacturers such as Vaillant, Mitsubishi, Daikin, Samsung and Viessmann.
How long does a heat pump last?
Typically 15 to 20 years with an annual service, which is longer than most gas boilers.
How much does a heat pump cost to install?
It depends mainly on the size of the heat pump, whether you need a new cylinder and how many radiators change. The grant comes off the total. You get a written, itemised quote after the survey.
Thinking about a heat pump?
Call 07852 979735 or use the form below. Tell me roughly how old your house is, how it is heated now and how many bedrooms it has, and I will tell you whether a heat pump is worth looking at.