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Retrofitting heat pumps: your complete guide

Retrofitting heat pumps

Heat pumps can be a fantastic – and low-carbon – alternative to traditional gas boilers. But we’re not all lucky enough to get one installed during the construction phase of a new build. So, what happens if you need to retrofit a heat pump?

Here, we’ll explore everything to do with retrofitting heat pumps in commercial and high-volume residential settings – from what’s involved to whether it’s worth it.

Can a heat pump be retrofitted?

Yes! Heat pumps can be retrofitted in most buildings – especially air source heat pumps, which are generally less expensive and easier to install than the alternatives.

A system designer will start with the building load. In other words, they’ll carry out heat loss calculations on your building, to work out what elements can be kept or changed when you make the swap to your new heating system.

They’ll then be able to design a bespoke solution to meet your needs, before installing your new heat pump with as little disruption as possible.

Is my building suitable for retrofitting a heat pump?

Most buildings are suitable for retrofitting a heat pump. However, some buildings can accommodate a heat pump with fewer alterations than others.

Here are some factors to bear in mind.


It’s possible to retrofit heat pumps in older buildings. In fact, there are many examples of successful heat pump projects with old buildings. However, the type of heat pump and refrigerant needs to be matched to the building and aspirations of the owner or operator.


Insulating a building will reduce the heat loss, which will reduce the size of heat pump needed and the energy bills for operating it. That said, heat pumps are available to any size and can meet any heat demand.

Existing heating system

Depending on your building’s existing heating system – and the refrigerant used in your heat pump – you may be able to keep your existing pipework.

Existing emitters

Some heat pumps run at a lower temperature than boilers. So, they tend to require larger emitters (eg. radiators, AHU coils etc.) for the same heat output. However, some buildings have oversized radiators, in which case, you may be able to keep them.

Other heat pumps such as the Clade Birch HT operate at boiler temperatures, in which case no changes to the building are necessary. This easy installation needs to be balanced with the heat pump efficiency, a decision that your designer will guide you through.

Outdoor space

An air source heat pump will need to be installed outside. For instance, in a car park or on a roof space.

Ultimately though, it’s not your job to work out whether your commercial building is suitable for a heat pump. Rather, that’s the job of your system designer.

A Clade engineer will be able to assess your premises and come up with a bespoke solution that matches your building and requirements perfectly.

How easy is it to retrofit heat pumps?

Retrofitting a heat pump can be a lot easier than you might expect. Especially if you choose a refrigerant with a temperature differential that closely matches those used by boilers – like the natural refrigerant R290 (propane).

Let us explain.

Most gas boilers are set up to operate at 80C with a 60C return temperature. The difference between these two temperatures is called the temperature differential, also known as the Delta T or DT.

Meanwhile, R290 heat pumps are normally operated at 60C with a 40C return temperature. Although these temperatures are lower than those used with gas boilers, the Delta T is a close match.

As most existing buildings are already set up to work with a Delta T in this ballpark, very few changes – if any – will normally need to be made to accommodate your new heat pump.

Even better, our high temperature R290 heat pumps operate at 80C flow and a 10C differential. This is as close to traditional boiler temperatures as it’s possible to get with a heat pump. This makes retrofit super easy.

On the other hand, some refrigerants require a little more work to retrofit – like CO2. While this natural refrigerant is highly efficient, non-corrosive and non-toxic, it’s completely different from boilers and further from the conditions that the industry is used to. So, it can present more of a technical challenge to implement.

Retrofit heat pumps

Can I add a heat pump to my existing system?

So, does this mean that a heat pump can be fitted to an existing heating system?

Yes, easily if you’re using our Birch HT heat pump.

And, if you’re retrofitting R290 using standard R290, then yes in most cases. You’ll be able to keep your building’s existing pipework and infrastructure to use with your new heat pump, instead of having to replace the whole system.

Not only does this keep installation costs down, but it also minimises disruption.

After all, it should be possible to keep your old boiler working through most of the installation period, only disconnecting it at the very last minute.

You should consider the impact that running heat pumps at different temperatures and temperature differentials has on operational efficiency. Make sure your designer advises you correctly on this so you understand the total lifetime impact of your heat pump.

Do heat pumps work with old radiators and emitters?

Wondering if you can keep your old radiators, fan coil units, air handling units or other emitters too?

Well, it all depends on the size and specification.

As most R290 heat pumps work at lower temperatures than boilers, you’ll generally need bigger emitters (radiators) to achieve the same heat output – although this is not true with our Birch HT heat pump.

However, in the past, many emitters have been oversized, making them suitable for lower flow temperatures.

Working out whether your radiators need to be changed is your system designer’s job. But there’s a simple test you can carry out yourself to get a good idea of whether you could keep your emitters.

Just turn your boiler down to 60C on the flow temperature over winter. This way, you’ll be able to see in real time how your building would feel on a propane system with your existing emitters.

Is it worth retrofitting a heat pump?

Wondering if it’s worth retrofitting a heat pump as opposed to investing in a replacement boiler?

Switching your boiler for a heat pump is well worth it.

But don’t just take our word for it. Here are the main benefits to help you make your own decision.

More efficient

Heat pumps are highly efficient. In fact, you’ll be able to generate more heat than the electricity you use to power your heat pump by up to 4 times.

A heat pump’s average efficiency is called its Coefficient of Performance (COP) or Seasonal Coefficient of Performance (SCOP) when aggregated over a year. Although a heat pump’s efficiency will vary based on lots of factors – like the refrigerant used and the temperatures outside – they generally achieve efficiencies of 300-500%, or a SCOP of 3-5.

In this way, they’re three or four times more efficient than gas boilers, which will typically operate at an efficiency of around 80%.

Lower running costs

The high efficiency of heat pumps can lead to lower energy bills, which is always a plus for savvy businesses looking for ways to reduce their operating costs.

Currently, the price of electricity is higher than that of gas. But you can reduce your costs still further by powering your heat pump with a renewable energy source such as solar PV.

Check out our open-air swimming pool case study to learn how we achieved this on a past project.

More environmentally friendly

Many businesses choose to retrofit a heat pump in order to reduce their carbon footprint. And indeed, switching to a heat pump can hugely reduce your business’ impact on the environment.

Although much of the UK’s electricity is still generated by fossil fuels, the proportion of renewable energy supplied to the National Grid is increasing. And besides, heat pumps are highly efficient.

That said, it’s also important not to underestimate the impact of your heat pump’s refrigerant. Heat pump refrigerants broadly fall into two categories – natural and synthetic.

Synthetic refrigerants are used in the majority of heat pumps manufactured today. But they are mostly harmful F-gases that have a devastating impact on climate change. They also release harmful ‘forever chemicals’ called PFAS into the environment, which poison wildlife and, in some areas, even endanger human health.

On the other hand, natural refrigerants won’t contribute to climate change, won’t damage the ozone layer and don’t contain harmful toxins. Hence why we only work with natural refrigerants here at Clade. So, they’re a no-brainer for businesses looking to have a positive impact on the environment.

Longer life expectancy

While traditional boilers typically only last for 10 to 15 years, commercial heat pumps typically have a lifespan of around 15 to 20 years.

A natural refrigerant heat pump will also be futureproof, as it won’t be subject to regulations like fossil-fuel-powered heating systems and harmful F-gases. In this way, you could view them as the best way to ensure your heating system doesn’t become a stranded asset in the near future.


Last but not least, heat pumps are incredibly flexible.

They can be used to produce heating and hot water. And they work well with a wide range of emitters at low surface temperatures for comfort and efficiency.

Heat pump retrofit

How much does retrofitting a commercial heat pump cost?

Every business has different needs, and this will have a big impact on your overall costs. For instance, as you would expect, heating an office is very different from heating an indoor swimming pool!

With that in mind, the cost of retrofitting a commercial heat pump will vary based on lots of factors, including:

  • The size of your premises
  • The building’s level of insulation
  • System power and efficiency
  • Required room temperature
  • Any noise reduction features needed
  • Whether you need a monobloc or split system (one that sits outside your building or one that has a unit both inside and outside)

Ultimately, although commercial air source heat pumps require a significant initial investment, it’s important to look at the long-term financial impact of your heating system – moving from a cost to an efficiency model.

Is there financial help available for retrofitting a heat pump?

There is a range of heat pump grants and funding schemes available to help organisations with the upfront cost of retrofitting a heat pump.

These include:

  • Public Sector Decarbonisation Scheme (PSDS)
  • Clean Heat Grant
  • Boiler Upgrade Scheme (BUS)
  • Social Housing Decarbonisation Fund

However, tax breaks are the most widely available support available to non-public sector organisations – it’s likely that heat pumps will qualify for the 50% first year allowance (FYA) for special rate plant and machinery (just bear in mind that we’re not tax advisors and you should get proper advice).

Although it won’t allow you to fully expense your heat pump, the 50% special rate FYA does represent a significant uplift for special rate assets, compared to the 6% writing down allowance.

Alternatively, at Clade, we have a heat-as-a-service offering. This helps businesses spread out the initial cost of a commercial heat pump.

Let us retrofit a natural refrigerant heat pump for you

As you can see, retrofitting a heat pump comes with a whole host of benefits, and could be much easier than you’d think.

If you’re toying with the idea of retrofitting a heat pump, get in touch with our team of engineers here at Clade. We’d be happy to assess your premises and retrofit a natural refrigerant heat pump that meets your requirements perfectly.