Ensuring that your building’s insulation is up to current standards is essential for ground source heat pump installations.

Insulation is the single most important aspect of any building. It is the easiest way to reduce any buildings heating costs and as energy prices spiral, fitting good quality insulation will save energy, reduce fuel bills and reduce carbon emissions. Good quality insulation has the fastest payback of any energy saving measure that can be fitted to a building.

Upgrading the insulation of any building should always be the first step before considering any renewable technology, particularly heat pumps. Do not look to renewable technology to compensate for poor insulation.

Only the best insulation should be fitted such as or Contrary to popular belief, mineral wool, fiberglass or polystyrene insulation are not particularly good insulators and we would not expect them to be used in new or renovated buildings. Other products such as Thermafleece can be used in some areas. This is a low embodied energy insulation product

As a minimum the buildings insulation level should be bought up to current standards and ideally should be increased above this.

For example any cavity walls in existing buildings should always be filled wherever possible. However this will not make an existing building well insulated and additional insulation will still need to be fitted.

Many existing buildings (except some Listed buildings) can become well insulated by adding insulation on the inside (or outside) of the walls, on the floors and in the roof.

It is generally accepted that a well insulated building would be considered to have about 100mm of good quality insulation (Celotex, Kingspan or equivalent) in the walls and floors, and about 200mm in the roof. A very well insulated building would have levels higher than this.

It is important that heat pumps are only installed in insulated buildings, this is because the lower the flow temperature from the heat pump, the higher it’s efficiency. In a poorly insulated building a higher flow temperature is required meaning the heat pump will cost more to run and have higher carbon emissions. If the building is very poorly insulated the heating distribution system (due to the low temperatures from the heat pump) might not be able to provide sufficient heat into the building and the occupants will feel cold.

Kensa Insulation

Retrofit-and-forget technology

Ground source heat pumps are a great replacement heating system for existing or renovated buildings. As well as providing reduced running costs, minimal maintenance costs, and peace of mind for a system with a 25 year lifetime, ground source heat pumps in retrofit properties will generate typically £xx every year for seven years under the Domestic RHI.

Read Kensa’s advice on this page about the factors you need to consider in order to progress with a ground source heat pump in a retrofit home.

Kensa Housing Project

Insulation is King

For a good heat pump installation on a renovated building, insulation is key.

Insulation is the single most important aspect of any building. It is the easiest way to reduce any buildings heating costs and as energy prices spiral, fitting good quality insulation will save energy, reduce fuel bills and reduce carbon emissions.

Ideally the insulation levels in the property will need to be such that there is a maximum peak heating demand of less than 50 Watts per square metre. This is approximately the level of insulation required to comply with Part L of the Building Regulations 2005 (Part F in Northern Ireland, and Part J in Scotland).

Can't insulate? Go bivalent

If there is no opportunity to improve the fabric insulation of the building a supplementary heat source could be used. This is known as a bivalent installation, where the existing boiler is retained to meet the peak demand of the building at the coldest times. As the boiler operates at a higher flow temperature, when in operation it will take the full load of the property effectively holding off the heat pump until it is capable of providing the level of comfort required. This can be done manually through time clocks or a more sophisticated automated system could be employed using external thermostats.

Bivalent installations can be effective, however a great deal of consideration needs to be given to the value of installing the heat pump in un-insulated buildings due to the capital cost involved, considering the running cost savings are likely to be marginal and the system performance may decrease in comparison to the existing boiler system due to the lower flow temperatures in the radiators.

Kensa Case Studies

Sizing it right

In in order that an accurate heat pump sizing can be determined all properties, regardless of the insulation levels, will need a full MCS heat loss calculation. This process typically costs around £150 – £200.

If the insulation levels are unknown and generally of a lower standard than current Building Regulations, then it may cost £300 – £400.

If a heat pump is too small then the running costs will increase, too large and the heat pump could cycle on and off.

Kensa or your installer will take care of this process for you.

Working with radiators

As radiators in retrofit properties are typically sized for a flow temperature of 71°C – 82°C, they may well be undersized to work with a ground source heat pump (which requires a flow of around 50°C). Therefore the radiators might need replacing.

To understand what the maximum output of the radiators are at the reduced temperature and whether they are large enough, Kensa recommend you consult a heating engineer.

Kensa Housing Project

Make the retrofit switch to ground source heat pumps

  • Guaranteed income for 7 years
  • Minimal internal disruption
  • Permitted Development Rights
  • High temperature models to fit with existing systems and build type
  • Removes costly reliance on fossil fuels
  • No reliance on fuel deliveries (if off gas)
  • No unsightly storage tanks (if using LPG)
  • 365 days of guaranteed heat and hot water

Fulfilment: How to buy



Experienced installers and self builders can utilise Kensa’s consultancy service through online and telephone based support and face to face training, ensuring an MCS accredited installation.

  • Consultancy Service



Use of a Kensa Approved Installer provides complete peace of mind and flexibility.

  • Approved Installer
GET A QUOTE0345 222 4328