Do I need to insulate my home before fitting a heat pump?

3 November 2021 Kingspan Insulation UK

The Government has announced that from 1st April 2022, homeowners will be able to apply for grants of up to £5,000 towards the cost of a heat pump via the Boiler Upgrade Scheme. This is a big moment, making these low carbon heating technologies much more affordable, particularly given the rise in gas prices. However, to ensure they perform efficiently and affordably, it is essential to first take some steps to ensure your home is well insulated. 

Why switch to heat pumps? 

The energy we use in our homes currently accounts for around 14% of total UK greenhouse gas emissions. To help address this, the Government has committed to decarbonising UK electricity by 2035. The UK has already reached a point where less carbon is generated from 1 kWh of energy from electricity, than from natural gas and it is projected that this will only improve as the grid decarbonises further. 

This means homes need to be transitioned away from fossil fuel heating systems (such as gas) to electrified alternatives. Heat pumps are a natural choice to replace gas boilers due to their highly efficient design. 

Heat pumps extract heat from either the external air (air source heat pump) or via pipes buried in the ground (ground source heat pump). This heat is used to evaporate a refrigerant which is then pressurised further – creating additional heat. Whilst a new boiler may achieve an efficiency of 92%, ground source heat pumps can reach efficiencies of 300% or more. This makes them far more affordable to run than direct electric alternatives.  

In addition to helping to shrink your carbon emissions, the switch to heat pumps should also make sense when it comes to your long-term energy bills. At present, gas is taxed at a lower rate than electricity. However, it is expected this will change over the next decade with surcharges reduced on electricity and added to gas. This means heat pumps will become increasingly cost effective to operate. 


Why insulation is important for heat pumps 

Whilst conventional gas boilers are often designed to operate at around 65°C to 75 °C, heat pumps perform most efficiently at far lower temperatures (typically 55 °C or below, with some operating down to 35°C). This is why it is often recommended that you fit underfloor heating at the same time as a heat pump. These systems distribute heat evenly across a larger area at a lower flow temperature. Alternatively, you may have to fit larger radiators to provide enough heat. 

This lower operating temperature also means it’s important to retain as much heat in your home as possible by properly insulating the walls, floor and roof. A well-insulated home will not only allow your heat pump to warm your house more effectively and affordably, it may also mean that you can have a lower capacity heat pump installed (or use smaller heat emitters) – reducing upfront costs. 

Having effective insulation is especially beneficial for homes with an air source heat pump. During the winter, the air temperature is lower which means these systems have to work much harder to generate the necessary heat. If your home allows a lot of heat to escape then this could significantly raise your heating bills or simply mean your home isn’t kept at a comfortable temperature. 

When fitting insulation, it is also essential to ensure your home is well ventilated – see the ‘what insulation should I install with my heat pump’ section for more information. 

How much can I save by fitting insulation with a heat pump? 

To give a clearer idea of how you can benefit from fitting home insulation with your heat pump, we carried out some energy modelling on three typical houses: 
  • a solid walled house which has no insulation measures. These were typically built prior to 1920 and can have very high levels of heat loss (annual energy usage 17000 kWh/year); 
  • an average cavity walled home with no insulation measures (11000 kWh/year); and 
  • an existing home with properly insulated walls, roof and floors (5000 kWh/year) 
For the comparison we used the Quarterly Energy Prices reported in March 2021.  
  If heated by a 92% efficient gas boiler with good controls If heated by a 100% efficient direct electric heating system If heated by a 250% efficient air source heat pump If heated by a 320% efficient ground source heat pump
  Efficiency adjusted kWh/yr demand £/year (gas) Efficiency adjusted kWh/yr demand £/year (electric) Efficiency adjusted kWh/yr demand £/year (electric) Efficiency adjusted kWh/yr demand £/year (electric)
Solid walled house (unimproved) 18478 628.26 17000 2958.00 6800 1183.20 5312.5 924.38
Average existing house (unimproved) 11957 406.54 11000 1914.00 4400 765.60 3438 598.21
Well insulated home 5435 184.79 5000 870.00 2000 348.00 1563 271.96

As you can see, for four heating technologies, the cost of heating the well-insulated home is less than half of the cost for an average home and almost a quarter of the solid walled house. Whilst there can be a notable cost for fitting measures such as solid wall insulation, bear in mind that they will continue to provide these significant energy savings throughout the lifespan of your home – making them a worthwhile long-term investment. 

Of the different heating methods, direct electric is by far the most expensive heating approach. The two heat pump options are also moderately more costly than the gas boiler option – particularly for the poorly insulated homes. Keep in mind, however, that the price of gas has risen significantly in recent weeks and can be expected to rise further in the future as taxes are adjusted. This means the gap in cost between these technologies can be expected to shrink significantly and heat pumps are likely to be the more affordable heating option within the next decade as well as having less carbon associated with their use. 


What insulation should I install with a heat pump? 

For the heat pump to perform most effectively, you’ll want to ensure that your walls, floor and roof are all properly insulated. The most appropriate measures will depend on the particular design of your home including a range of factors such as your home’s size, location, orientation and the construction and condition of your walls, floor and roof. 

To help identify the best measures, we recommended having your home assessed through the PAS 2035 process. This requires a qualified retrofit expert to carry out a full assessment of your home and identify a clear package of improvement measures to be fitted up to 2050.  

In addition to finding the most suitable insulation, they will also look at what repairs may be needed to address existing issues such as damp or condensation and whether additional ventilation is needed.  This is crucial, as when insulation is installed, it will prevent draughts and other air leaks, making your home more airtight. If adequate ventilation is not added to replace this, it could lead to serious issues. 

 Learn more about why ventilation is important when fitting insulation. 

The retrofit expert will also make recommendations for other simple measures you can take to improve efficiency, such as fitting smart thermostats which learn when you’re in the house, to further reduce your long-term bills. Depending on your goals, they may suggest additional measures such as PV roof panels to help provide power for your home and heat pump. 

Learn more about PAS 2035. 

How can we help you?