Heat pump warning: are they suitable for older homes?

After warnings from Bosch, we investigate if ground source or air source heat pumps are suitable for older properties, and how much space you’ll need.

Thinking of installing a heat pump in your period property? Home appliances manufacturer Bosch may have just thrown a spanner in the works, labelling heat pumps as an impractical and potentially inefficient option for old houses. This news comes as the Government is trying to encourage the domestic installation of heat pumps to meet net zero targets. 

Bosch told The Telegraph that Britain’s older Victorian housing stock is unsuitable for the installation of heat pumps, as older properties lack space and have insufficient insulation. However, new homes are suitable for heat pumps because they’re better insulated and have more space to accommodate the large equipment, says the company.  

But why are heat pumps such a problem in older homes? “At low temperatures you need well-insulated homes, you also need space for heat pumps for the external unit and the tank, so you have to have the sort of home which is adequate around the heat pumps,” explains Vonjy Rajakoba, managing director of Bosch UK, in The Telegraph article.  

Worcester Bosch, which is part of Bosch, makes both heat pumps and conventional boilers. 

Air source heat pump located against an outside brick wallCredit: Shutterstock/klikkipetra

Know your heat pumps

According to the Energy Saving Trust, heat pumps capture heat from outside and move it into your home. The amount of heat generated is much greater than the quantity of electricity used to power the system, which makes them much more efficient than other heating systems. There are two types of domestic heat pumps in the UK – ground source heat pumps and air-source heat pumps 

Air source heat pumps
These are the most common and transfer heat from the outside air to water, which heats your radiators or underfloor heating. There are two types: monobloc and split systems.

A monobloc system has all the components contained in a single outdoor unit, and pipes carry water to the central heating system and a hot water cylinder located inside your home. A split system consists of an outdoor fan unit and an indoor hydro unit

Ground source heat pumps
As the name suggests, these systems transfer heat from the ground outside your home to heat your radiators or underfloor heating. They can also heat water stored in a hot water cylinder for your hot taps. 

How do they work?
Air-source heat pumps work at a lower internal temperature than gas or oil-fired boilers, providing gentle heat to your radiators for longer. However, they don’t offer quick boosts of heat, and according to The Eco Experts, an air source heat pump may lose efficiency as it gets colder, as it has to use more energy to draw warmth from the air. 

Are heat pumps unsuitable for certain types of home?

We spoke to Stephen Bielby, operations manager at the Ground Source Heat Pump Association. He disagrees with Bosch’s claim that heat pumps are totally unsuited to older homes: “Any building will leak heat regardless of source, and all buildings and all heat technologies will benefit from a degree of energy efficiency or building fabric improvements. At this point in time, society must decide between leaking lower-cost, very-high-carbon heat (gas), or slightly more expensive, increasingly low-carbon heat (electrification with a heat pump).” 

Bielby also refers to a report published by Energy Systems Catapult, a body set up to accelerate the transformation of the UK’s energy system to net zero. “Apart from reporting steadily improving efficiencies (over previous trials), this programme could not identify a dwelling where there was no individual heat pump solution, be it air source, ground source or hybrid (a combination of a heat pump and a fossil fuel boiler).” In other words, there’s a suitable heat pump for every home.

Do heat pumps really need more space?

The space required for gas boilers is quite different to that require by air source heat pumps and ground source heat pumps, as heat pumps come with some extra equipment.  But you won’t need a regular boiler, meaning you can regain this space. 

Air source heat pump 

With an air source heat pump, you’ll need to have a large box on the outside of your home and about two metres of clear space in front of the unit. The size of the unit will vary depending on the manufacturer and kilowatt output.  

Apart from the outside unit you’ll also need a hot water cylinder inside your home, and the size of the cylinder installed will depend on the usage requirements for the property.  

Exceptional asked heating, ventilation and air-conditioning manufacturer, Vaillant for some guidance on the ‘average’ size of the equipment: 

  • External air source heat pump (monobloc and split system), based on Vaillant’s 7kW aroTHERM Plus: 110cm x 96.5cm x 45cm (43in x 38in x 13in)
  • Internal unit (split system only), based on Vaillant’s 7kW aroTHERM Split: 44cm x 77cm x 35cm  (17in x 30in x 14in)
  • Hot water cylinder, based on Vaillant’s 200 litre uniSTOR cylinder: 126.5cm x 59.5cm (50in x 23in)

Ground source heat pump

For a ground source heat pump, you’ll need land near your home that’s suitable for drilling boreholes or trenches. Inside your home, you need space to fit an indoor heat pump, which often contains the hot water cylinder. You can expect this to be about the size of a large-style fridge, according to the Energy Saving Trust 

  • Ground source heat pump, based on Vaillant’s FlexoTHERM: 118.3cm x 59.5cm x 60cm (47in x 23in x 24in) 
  • Hot water cylinder, as above

Rajakoba’s acknowledges that some heat pumps do need more space inside or outside the home. But he explains that there are ways to mitigate this. “Where homes may be unsuitable for an external unit, these could be served with an internal ground source heat pump,” he says. “Or they could connect to a heat network that will almost certainly end up being driven by a centralised commercial heat pump, even if not from the outset.” 

Having the space for a hot water cylinder can also be a challenge, especially if your gas boiler is in a kitchen cupboard. Bielby says: “There are space-saving technologies, such as phase change storage devices, which have the potential to reduce the size of the cylinder by 75%.” 

Rajakoba’s comments come at a time when the Government is backing the installation of domestic heat pumps. The £60 million Heat Pump Ready Programme is providing funding for the Government’s target of 600,000 heat pump installations a year by 2028. This is being supported by a £450 million three-year Boiler Upgrade Scheme, offering households grants up to £5,000 for low-carbon heating systems.  

What are the alternatives for older homes?

Bosch believes that hydrogen boilers are a more practical solution for older properties. However, the future for hydrogen boilers is still being determined, with major infrastructure barriers to overcome. For example, the national gas grid would need converting and pipes replaced in gas customers’ homes.  

There are other options for heating hot water, especially solar panels, although you can’t usually use them to heat your home, according to the Energy Saving Trust. You will also need to check if you can have solar panels installed. There may be restrictions if you live in a listed building, a conservation area or a national park. 

If you are thinking of installing a heat pump, it’s a good idea to ensure your home is properly insulated from the top down before you make the investment. Although key to any heating system, appropriate insulation is particularly pertinent with heat pumps, which work at lower internal temperatures. The Exceptional team will be sharing more news and features on heat pump development, so keep an eye on our updates. 

Camilla Sharman

Written by Camilla Sharman she/her


With her 30 years of experience, Camilla Sharman has covered a wide range of sectors within the business and consumer industries both as a feature, content, and freelance writer.  As a business journalist, Camilla has researched articles for many different sectors from the jewellery industry to finance and tech, charities, and the arts. Whatever she’s covered, she enjoys delving deep and learning the ins and out of different topics, then conveying her research within engaging content that informs the reader.