As part of our involvement with this year’s HOMES UK conference, Partners John Milner and Ian Maun spoke at a session about the proposed future ban on gas boilers in new homes and alternative heating sources that can be considered as a replacement.

New Build Homes

To set the scene, the UK Climate Change Act (2008) set legally binding targets for reducing CO2 emissions in the UK by at least 80% by 2050, compared to the 1990 baseline emissions. This act is supported by the UK Low Carbon Transition Plan (2009) which set-out the UK’s approach to meeting our carbon reduction commitments.

Most recently (at the time of writing), the UK Government has accepted the Committee on Climate Change’s 4th carbon budget recommendations which cover the period 2022 to 2027 which set a CO2 reduction target in law of 50% reduction by 2027 (again from the 1990 baseline). Then in the Spring Statement in March 2019, the UK Government made the bold statement that gas heating for new houses would be banned by 2025.

Following on from this and in the run up to the COP26 Climate Change Summit to be held in Glasgow next year, the Prime Minister outlined his “10 Point Plan” on 18th November 2020 for a “Green Industrial Revolution”. It was widely reported during this announcement that the 2025 target was going to be further reduced to 2023, but this has subsequently been withdrawn and there seems to be a little confusion as to whether the target is now 2025 or 2028.

However, whenever the target date is, it is clear that gas will not form part of the future for heating new build homes.

Building Regulations

The control of energy in new dwellings is governed by Part L1A of the Building Regulations which sets maximum limits for CO2 emissions by setting minimum fabric energy efficiency standards for new dwellings. There are separate versions of Part L in the devolved nations, but they fundamentally all use the same methodology to calculate carbon emissions, energy use and fuel costs, namely SAP (Standard Assessment Procedure).

Part L of the Building Regulations has been under review for a number of years with an extensive consultation exercise that commenced in 2019 under the “Future Homes Standard” which was due to feed into updated Building Regulations late in 2020. This review has not yet been concluded due to wider issues, such as Brexit and Covid-19.

It has, however, been recognised that the original version of SAP was unduly penalising the use of electrically generated heat sources, and consequently part of the Future Homes Standard consultation process included a new SAP procedure known as SAP 10.

As a result, from January 2019, planning applicants across the country were encouraged to use the updated SAP 10 carbon emission factors to assess the expected carbon performance of a new development. As a result, the carbon factor for electricity is reduced by approximately 45%, which results in fuel factors of       0.210 kgCO2/kWh for gas and 0.233 kgCO2/kWh for electricity, bringing us much closer to parity as a result of the de-carbonisation of the electricity grid via the use of wind and solar energy farms.

Lean, Clean, Green

The mantra of Lean, Clean and Green is as important as ever. To reduce carbon and energy bills for residents, the following must apply:

  • Lean: a fabric first approach to reduce the amount of energy required in the first place to heat our homes. The direction of travel here is very much towards increased wall construction thicknesses and better air tightness, which will make Passivhaus standards the ever more likely goal.
  • Clean: to supply clean energy within the UK, which means continuing with the de-carbonisation of the electricity grid.
  • Green: to use renewable energy sources as much as possible, which creates a significant role for Heat Pumps.
Introducing Heat Pumps

We’ve all been using heat pumps for years – the most common example being a fridge, which is essentially an insulated box with a heat pump system connected to it. A heat pump is an electrical device that extracts heat from one place and transfers it to another. The transfer of heat is via circulating a refrigerant through a cycle of evaporation and condensation. A compressor pumps the refrigerant between two heat exchanger coils. In one coil the refrigerant is evaporated at low pressure and absorbs heat from its surroundings. The refrigerant is then compressed en-route to the other coil, where it condenses at high pressure, and at this point it releases the heat absorbed earlier in the cycle.

There are two basic types that can be used to generate heat as follows:

  • Air Source Heat Pumps – absorb heat from the outdoor air
  • Ground Source Heat Pumps – draw heat from the ground or ground water

Both of the above transfer the heat they draw to a heating and/or hot water system within a dwelling via a heat exchanger.

Currently, the ability to reduce carbon emissions in the UK is restricted by the efficiency of gas boilers to convert gas to heat. Gas boiler technology can only be improved so far and 89% efficiency is the best that can realistically be hoped for, meaning that the UK will not be able to get to a Net Zero position if we continue using gas. Conversely, Heat Pumps have high efficiencies of at least 300%, providing a real opportunity to drive towards the Net Zero goal.

Other Emerging Technology – Hydrogen

Hydrogen can be considered a Zero carbon fuel as the output is water when it is burned to produce heat. In theory, we can introduce more hydrogen into the gas network to reduce its carbon intensity. £500M has been included for it in the 10 Point Plan and it has recently been announced that 300 Scottish homes are going to be connected to a pure hydrogen grid through the H100 Fife project.

However, there are two issues with hydrogen.

Firstly, it’s quiet explosive. Homes have been constructed at a UK test site with hydrogen-ready domestic boilers installed to evaluate safety, and results will come from that evaluation in due course.

Secondly, the carbon intensity of hydrogen is high compared to other forms of low carbon heat, meaning that it is likely to be used to a limited extent in domestic properties in the near future. Using an electrolyser with low-carbon electricity input to produce hydrogen to burn in a gas boiler results in only a 62% efficiency compared to 230 – 410% efficiency for a heat pump with the same input.

There will, therefore, be choices to made about the allocation of low carbon electricity and hydrogen boilers could only be suitable for properties where all other avenues are too difficult for example in heritage buildings.

A final issue on hydrogen is that, as many buildings transition to electric-based heating, it may result in a dwindling number of residents carrying the cost of maintaining gas networks.

The government also consulted on Green Gas levy to support the injection of bio methane into the gas grid to reduce its carbon intensity.

Data, data, data and strategy for existing homes

In the UK, we have the oldest housing stock in Europe. 85% of our existing homes rely on natural gas and 25% of our CO2 emissions arise from residential gas networks. To achieve net zero by 2050 we’re likely to have to undertake 27 million deep or incrementally-led retrofits.

Our homes are our biggest national infrastructure asset, but we have a complex multi-faceted market, and this asset is not treated strategically – there is no a big plan, quite a few shorter-term interventions and historically confusing signals.

So, in retrofit, what can organisations do to prepare for the future and no gas?

The simple answer is data, data, data, or strategic active asset management.

The end of gas can’t be considered in isolation. There are a few archetypes where electric for gas replacement will work on both capital and running costs, but organisations need to collect all their data on hard to treat homes, air tightness, ventilation, existing component condition etc. to get a full picture.  In other words, a 29-year stock-based strategy to get to net zero is required and it won’t include much natural gas. Such a strategy needs to be modular so that it can identify packages of work or components that can be called off to benefit from available funding such as the social housing decarbonisation fund.

Such a strategy is likely to identify incremental and whole house retrofit and replacement. It will also involve training. Our education system does not currently support retrofit training and skills to any great extent but initiatives such as the scaling up of retrofit education or SURE are starting to come through.

PAS 2035

But how do we avoid the problems of poor quality, a performance gap, increased bills and poor resident experience of some past retrofit projects, where following the money often resulted in some poor and perverse outcomes?

It is our opinion that anything more than a simple gas to electric heat source swap that involves improving the thermal envelope and ventilation should be carried out as outlined in PAS 2035. This is a quality control process with specific roles, such as retrofit coordinators, and involves risk assessment and the production of medium-term improvement plans for each property. An example of the good practical advice included in PAS2035 is the retrofit measures interaction matrix which is an effectively part of a risk based approach to the complementary, part complementary and non-complementary individual retrofit measures.  

Retrofitting heat pumps

When it comes to retrofitting heat pumps, one of the key issues is that heat pumps are more effective at lower temperature flows and returns. They are therefore dependent upon an efficient thermal envelope, effective air tightness and ventilation strategies and longer flatter load profiles, which may require changes in resident behaviour.

The Government’s recent 10 Point Plan requires 688 thousand heat pumps per annum by 2028 and the Committee on Climate Change estimates that 19 million heat pumps will be required by 2050 or 633 thousand per annum. The renewable heat incentive has funded 9900 installations per annum in the UK since 2014 so there is a clear gap in funding and the current policy environment is unlikely to fill it. The capital cost of heat pump installations combined with building envelope performance upgrades to achieve the net zero target will require funding support.

An example of such funding is the Social Housing Decarbonisation Fund. We have recently assisted one of our clients in producing a bid for works which improve the thermal envelope and airtightness of two sets of buildings and introduce an 8.5 kilowatt air source heat pump for each one.

The GLA has also recently launched the retrofit innovation partnership to deliver Energiesprong projects at scale within Greater London. Energiesprong is based upon a performance guarantee with the difference between the utility bills before and after work funding the refurbishment. This is a whole house retrofit approach targeting a space heating goal of 30 kilowatt hours per metre squared per annum which is very challenging and will often include an air source heat pump and an all-electric solution. The solution is not prescribed but is likely to be a no gas solution due to the performance metrics required. We are currently working with a local authority client on a pilot scheme of eight properties.


From a new build perspective, the 2025 target is looming, so the industry needs to rely on tried and tested solutions, hence the significant take up on heat pumps. Consideration of these technologies along with early engagement of Building Services and Sustainability experts in conjunction with a higher performing fabric approach is essential, reinforcing the Lean, Clean, Green approach.

When it comes to retrofitting the existing housing stock, it’s clear that funding and training will play a key part in whether we can meet the targets of net zero by 2050, but if we can strategically consider the stock as a whole, there are options available to make significant improvements.