At Thermodynamics South Yorkshire, we specialise in designing heat pump systems around the property rather than taking a one-size-fits-all approach.
Before recommending equipment or replacing existing heating components, we carry out detailed heat-loss calculations and assess the existing heating system to establish what can be retained and what, if anything, needs to be upgraded.
The Property
This installation in Chesterfield is a good example of this approach. The 1950s semi-detached property had relatively new radiators, copper pipework and a relatively new unvented hot water cylinder.
Rather than automatically replacing these components as part of the heat pump installation, we assessed each part of the existing system and designed the new system around it.
The result was a 5 kW Samsung R290 heat pump installation in which the existing radiators, heating pipework and hot water cylinder could all be retained.
The property is a 1950s semi-detached house in Chesterfield.
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Property type: 2-bedroom semi-detached
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Bathrooms: 1
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Floor area: 86 m²
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Property age: 1950s
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Existing heating: Gas boiler
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Existing radiators: 8 radiators plus bathroom towel rail
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Existing hot water cylinder: Telford Tempest 125 litre unvented cylinder
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Existing heating pipework: Copper, with a mixture of 10 mm and 15 mm pipework
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Calculated heat loss: 4.07 kW
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Design outdoor temperature: -2.4°C
The customer had already carried out renovation work to the property, meaning that much of the existing heating system was relatively new.
This presented an opportunity to see whether the existing system could be retained rather than replacing components unnecessarily.
The Heat-Loss Calculation
The starting point for the system design was a room-by-room heat-loss calculation.
The calculated heat loss for the entire property was 4.07 kW, based on a design outdoor temperature of -2.4°C.
This figure was important when selecting the heat pump. Rather than selecting a significantly oversized unit, the system was designed around the property's actual heat requirement, with a 5 kW Samsung EHS Mono R290 heat pump selected to closely match the calculated heat loss, providing 4.95kw at a maximum designed 53 degree flow temperature.
The design flow temperature was set at 53°C at the -2.4°C design outdoor temperature.
This represents a conservative design condition intended to ensure that the system can continue to provide the required heat during colder winter conditions while allowing the heat pump to operate efficiently. If outdoor temperatures fall below the design temperature, the heat pump is capable of modulating its output accordingly.
The system was designed around a 5°C temperature differential (ΔT).
Could the Existing Radiators Be Retained?
One of the main questions during the design process was whether the existing radiators could provide enough heat at the proposed heat pump flow temperature.
The property had:
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3 × K2 radiators
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5 × K1 radiators
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1 × bathroom towel rail
Rather than assuming that the radiators would need to be replaced, we assessed them individually against the calculated heat loss of each room.
The calculations showed that the existing radiators were capable of meeting the required heat output at the design conditions.
Example: Kitchen
Calculated room heat loss: 1,227.39 W
Existing radiator: K2, 600 × 1,400 mm
Radiator output: 1,312.58 W
The existing radiator therefore provided sufficient output to meet the calculated heat loss of the room.
Example: Living Room
Calculated room heat loss: 1,298.64 W
Existing radiator: K2, 600 × 1,800 mm
Radiator output: 1,483.64 W
Again, the existing radiator provided sufficient output at the design conditions.
The same assessment was carried out throughout the property.
The result?
None of the existing radiators needed to be replaced.
This avoided unnecessary disruption and saved the customer the cost of replacing eight radiators that were already capable of doing the job.
Retaining the Existing Pipework
The property had an existing copper heating system.
The pipework consisted of:
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20 mm pipework from the existing gas boiler
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A mixture of 10 mm and 15 mm copper pipework throughout the property
There was initially no reason to assume that the pipework would be unsuitable for a heat pump.
Once the heat-loss calculation and system design had been completed, the existing pipework was assessed against the required flow rates.
The calculations confirmed that the existing pipework was capable of delivering the required flow rates for the new heat pump system.
As a result, the existing heating pipework was retained.
This is an important part of heat pump system design. Existing pipework should not automatically be considered unsuitable simply because a property is being converted from a gas boiler to a heat pump. Its suitability needs to be assessed against the requirements of the proposed system.
Reusing the Existing Hot Water Cylinder
The property also had a relatively new 125-litre Telford Tempest unvented hot water cylinder.
Replacing this cylinder with a new heat-pump-specific cylinder would have been an unnecessary additional cost if the existing cylinder could be adapted appropriately.
A conventional unvented cylinder uses a coil to transfer heat from the heating system into the domestic hot water. The surface area of a standard coil may not be sufficient for efficient heat transfer from a heat pump.
Rather than replacing the cylinder, we installed a domestic hot water cylinder plate loading 20 × Plate Kit.
The plate-loading arrangement allows the existing cylinder to be used with the heat pump by bypassing the existing cylinder coil and transferring heat through a plate heat exchanger.
The existing cylinder itself was retained, with no replacement of the cylinder or its existing controls, sensors or valves required.
This approach saved approximately £500 compared with installing a new heat-pump-compatible cylinder.
The Heat Pump System
The new system uses a 5 kW Samsung EHS Mono R290 integrated heat pump. The outdoor unit was installed in the rear garden, underneath the kitchen window.
System design
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Heat pump: Samsung EHS Mono R290
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Output: 5 kW
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Calculated property heat loss: 4.07 kW
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Design outdoor temperature: -2.4°C
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Design flow temperature: 53°C
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Design ΔT: 5°C
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Heating zones: 1
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Volumiser: 25 litres
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Controls: Samsung controls
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Radiators: Existing radiators retained
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Heating pipework: Existing pipework retained
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Hot water cylinder: Existing 125-litre cylinder retained and adapted with plate-loading kit
A 25-litre volumiser was incorporated into the system design.
Radiator Controls
Another consideration was how the radiators would be controlled.
The existing thermostatic radiator valves were removed from most of the radiators. The bedrooms retained their TRVs because customers generally prefer to have independent temperature control in bedrooms.
Removing unnecessary restrictions from the main heating circuit allows the heat pump to operate with the required system flow rather than having multiple radiator valves continually restricting circulation.
The result is a system designed to allow the heat pump to operate freely while still giving the occupants temperature control where it is most useful.
Installation
The installation took approximately five days.
As part of the installation, we:
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Decommissioned and removed the existing gas boiler
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Installed the Samsung 5 kW R290 heat pump
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Connected the heat pump to the existing heating pipework
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Retained the existing radiators
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Installed the 25-litre volumiser
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Adapted the existing Telford Tempest cylinder using the plate-loading kit
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Installed and configured the Samsung controls
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Commissioned the complete heating system
Because we are Gas Safe registered, we were also able to safely decommission and remove the existing gas boiler as part of the installation.
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The Cost
One of the biggest benefits of the design approach was the reduction in unnecessary replacement work.
Because the existing radiators, heating pipework and hot water cylinder were all suitable for retention, the installation did not require the additional cost of:
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Eight replacement radiators
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New heating pipework
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A replacement hot water cylinder
The total installation cost was:
£10,181
The customer received a £7,500 Boiler Upgrade Scheme (BUS) grant, bringing their total contribution to:
£2,681
The ability to work with the existing heating system therefore made a significant difference to the overall installation cost.
The Result
The system has now been operating since March 2026, and the customer is very happy with both the efficiency of the system and the warmth of the property.
Most importantly, the installation demonstrates that converting a property to a heat pump does not automatically mean replacing the entire heating system.
In this case, detailed system design allowed us to retain:
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All 8 existing radiators
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The existing copper heating pipework
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The existing 125-litre hot water cylinder
Only the components that needed to change were changed.
What This Installation Shows
This installation demonstrates why we believe heat pump design should begin with the property rather than with a list of components to replace.
The property had a calculated heat loss of just 4.07 kW, and the existing heating system had already been improved through previous renovation work.
By carrying out room-by-room heat-loss calculations and assessing the existing radiators and pipework, we established that they could work with the proposed system at a 53°C design flow temperature.
The existing hot water cylinder presented a similar opportunity. Rather than replacing a relatively new cylinder, we adapted it using a plate-loading kit, allowing it to work with the heat pump.
The result was a system designed specifically around the property, with considerably less replacement work and a much lower installation cost for the customer.
In short: we didn't replace what didn't need replacing.
Heat Pump Installations with Thermodynamics
At Thermodynamics, we specialise in air source heat pump installations and support homeowners through every stage of the Boiler Upgrade Scheme in Sheffield, Doncaster, Worksop, Retford, Chesterfield and Gainsborough. From assessing your home’s suitability and system design to managing the BUS grant application and completing a high-quality installation, we handle the entire process.
If you’re considering upgrading your boiler and want to take advantage of the BUS grant, get in touch with Thermodynamics today for expert advice and a personalised quote.