Carbon Legacy Ltd


Woodgate Farm

East Leake



LE12 6Pw


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Why choose a heat pump?

In the context of ever rising energy costs and climate change, every household is in need of a heating technology that is future-proof, cost-effective and independent of fossil fuels.

South Facing Rear Solar Pv - Carbon Legacy
Photograph by Carbon Legacy

Our environment is full of energy, even at sub-zero temperatures there is plenty of energy available.

Heat Pumps use conventional refrigeration technology to extract the sun’s energy stored in the environment and raise it to a temperature suitable for heating purposes. This principle works even in the middle of winter at temperatures as low as -25°C.

How The Trusted Technology Works

A Nibe heat pump for example; offers you three different future-proof heat sources: outside air, the ground or water.

  • 25% of the energy is sourced from the national grid in the form of electricity. This electricity is used to operate the heat pump’s refrigerant compressor, pumps and fans.
  • The other 75% of the energy is taken from the environment i.e the air or ground and transferred to the heat pump.
  • The energy from the air or ground is transferred to the refrigerant inside the heat pumps evaporator. This causes the temperature of the refrigerant to rise and change state from liquid to gas.
  • The refrigerant gas is then compressed, using an electrically driven compressor, reducing its volume but causing its temperature to rise significantly.
  • A heat ex-changer (condenser) then extracts the heat energy from the hot refrigerant to heat water for central heating, underfloor heating or domestic hot water.
  • After giving up its heat energy the refrigerant turns back into a liquid and is able to absorb energy from the environment again, allowing the cycle to then be repeated.

Benefits of the outside air as a heat source

  • Can be utilised all year round between -25ºC and +35ºC. It’s always available and seen as an inexhaustible source of heat.
  • It is the cheapest form of Heat pump technology and there is no need for a large area of land for ground collectors.


In this day and age, with skyrocketing fuel bills and the Governments introduction of the “Boiler upgrade scheme” (BUS) public subsidy starting in April 2022, an increasing number of people are turning to alternative means to heat their buildings. The BUS ASHP subsidy will be £5,000/installation and available on a first come first served basis for 3 years with a target of 30,000 homes/year.

Already popular in Europe, air source heat pumps are a low-maintenance, cost-effective means of heating your home.

Generally fitted outside a house, they work by absorbing the free and sustainable latent energy in the air; capturing outside heat in order to generate enough green, low cost energy to heat your building through underfloor heating systems, radiators, and even provide domestic hot water.

Benefits of the outside air as a heat source

Air-to-air heat pumps– extracts latent heat from the outside air and the heat then used to heat the air within you home in a similar way to an air conditioner. They tend to be used on a room by room basis where specific rooms need heating and often cooling in the summer.

Air-to-water – used to heat water in the same way a boiler does. Very suitable for use with underfloor heating. Can also be used to replace a standard boiler with some system changes and radiator upgrades. Please remember a ASHP has a general maximum flow temperature of 50 degrees C unlike a gas or oil boiler running at 70-80. The only time the radiators will not need upgrading in size is when building insulation improvements take place at the same time to reduce the buildings heat loss. It is critical that you get a MCS approved company such as Carbon Legacy to carry out detailed room by room heat loss calculations and demonstrate the potential running cost and CO2 savings achievable with an ASHP system. Please remember in older poorly insulated properties, it may not be possible to achieve running cost savings against mains gas.

So, if the idea of saving money, helping the environment by reducing your CO2 emissions by up to 50% then have your building assessed by us for free.



Ground sourced heat pumps (GSHP) are often the more expensive renewable heating option but they bring the highly desirable benefits of being the most reliable, efficent and lowest maintenance solution available today.

This is demonstrated by the 3 million worldwide installations, with many now over 20 years old. Carbon Legacy’s involvement goes back to 1999 when David Hill, Carbon Legacy’s Managing Director, was the developer of the seventh UK GSHP installation for a new office building in Nottingham. This was a very successful world first that provided commercial heating and cooling.

Having been involved in hundreds of domestic and commercial installations and with the benefit of 21 years’ worth of independent monitoring, we have the confidence to know what a well designed and installed GSHP can consistently deliver. Points to consider when thinking about a GSHP are:

  • Do not be misled by manufacturer’s claims on performance. What you need to know is the yearly performance average or average co-efficient of performance (seasonally adjusted COP) for a building similar to yours.
  • An effective system can have an average COP of 3.5 and above. This means that for every one kWh of electricity used by the heat pump you will get 3.5kwh of useful heat into your building or hot water system.
  • There are 3 basic types of ground collectors; closed loop boreholes, closed loop trench slinkies and “open” water river/lake/sea and ground water sources. Closed loop either in bore holes or trenches is the most commonly used solution. What will suite your situation will depend on site constraints and your budget. Open water solutions using river water or water extracted from boreholes can have very high efficiencies of over 5 COP, however they are dependent on Environment Agency approval and require a lot of up front and expensive investigation and so are usually only considered for larger commercial installations.
  • In-trench “Slinkies” (buried water pipe coils) are by far the cheapest solution and prove to be very effective where there are large areas of open space/land available. This can be in large gardens, adjacent fields or even under car parks/playgrounds etc.
  • When we have been involved in the design of very low energy buildings we have even successfully installed “in-foundation trench Slinky ground collectors”.
  • Where existing buildings have little available external space then vertical closed loop ground collectors in bore holes are used. These provide a problem-free, efficient solution but do have a high initial cost. The other advantage is that almost any ground type can be utilised from hard to soft rocks even in suburban built up areas and under buildings.
  • To work at their best efficiency heat pumps like to be connected to lower temperature heat emitters such as under floor heating. Removing an old boiler and directly replacing it with a heat pump will not work. Radiator sizing is crucial in the overall system design, to realise the savings from GSHP’s.
  • Some manufacturers will tell you that their high temperature heat pump (65 degrees output) can be used with your existing radiators; which it can, but only at the expense of efficiency and increased running costs (reduced COPs of 2-2.5) which then make the financial case very weak or even cost you more to run than your old system.

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