Does your house have an EPC (Energy Performance Certificate)? If you purchased it since 2007 and it is not a listed building, it will have. Your EPC will make some recommendations to improve your home’s energy efficiency – take a look at them. Does it recommend a heat pump? I can tell you now it does not. Even if your house is currently heated by an old, inefficient oil boiler the EPC will not recommend a heat pump – it will recommend that you install another fossil fuel consuming boiler. No EPC ever recommends a heat pump or any other renewable energy source for space heating.

This is very strange since it is government policy to encourage the uptake of heat pumps as part of its strategy to reduce CO2 emissions. In 2014 the Government introduced the Domestic Renewable Heat Incentive to encourage the installation of renewable technologies and especially heat pumps. It followed a scientific study of over 40 heat pump installations carried out by the Energy Saving Trust in 2013. The study concluded that:

“The evidence obtained through this study indicates that correctly installed and operated heat pumps can perform to a very high standard in UK homes. Our methodology focused on measuring the efficiency of the monitored heat pumps by calculating Seasonal Performance Factor (SPF). This is simply defined as the amount of heat the heat pump produces compared with the amount of electricity needed to run the system (including auxiliary, immersion heaters and circulation pumps). The average SPF for an air source heat pump was found to be 2.45. For ground source heat pumps it was found to be 2.82. Heat pumps are much more efficient than direct electric heating.” 1

That was in 2013. Since then there have been numerous improvements to heat pump efficiency and the adoption of MCS (Microgeneration Certification Scheme) standards by the industry has improved the quality of installations and heat pump performance. My own company, based in Harrogate, has installed nearly 200 heat pumps most of which achieve SPFs of 3 or better for space heating. A further study carried out in 2013 by the Energy Saving Trust on behalf of Mitsubishi Heat Pumps (the largest supplier of air source heat pumps in the UK) concluded:

“The heat pumps demonstrated average estimated annual operating cost savings of 8% over a gas condensing boiler, 36% over an oil condensing boiler and 67% over a direct electric heating system. Estimated carbon emission savings of 21%, 41% and 67%, respectively, were also demonstrated. After future grid decarbonisation, these carbon savings rise to 85% for gas and 88% for oil.” 2 

So why in 2019 are EPCs not recommending heat pumps? In fact, contrary to the field studies carried out on behalf of the Government, and contrary to the evidence of all the installations my own company has carried out, EPCs consistently predict that a heat pump will cost more to run than even old, inefficient fossil fuel boilers. Why is this?

The answer lies in the fact that the algorithms producing EPC reports are fundamentally flawed. EPCs have never advocated non-fossil fuel alternatives to space heating in their recommendations (they do recommend solar photovoltaic and solar thermal systems for electricity and hot water) and have always underestimated the efficiency of heat pumps relative to other heating systems.

In 2017, however, the situation became even worse when BRE (the Buildings Research Establishment) produced the “SAP REVISED HEAT PUMP PERFORMANCE METHOD” 3. SAP (Standard Assessment Procedure) is the methodology used by the Government to assess and compare the energy and environmental performance of dwellings. The revised SAP astonishingly adds up to a third to the energy requirement of a home if a heat pump is the heat source. Please see below two EPCs for the same building with only one parameter changed in the input data – the choice of heat source. The energy required to heat the building when a heat pump is chosen leaps up from 78,249kWh per year with an oil boiler to a staggering 110,006kWh per year with a heat pump. This is not only incorrect it defies the laws of physics!

The choice of heat source cannot possibly affect the heat demand of a building. Moreover, the running costs predicted by the EPC are double that of the oil boiler. This contradicts the studies which were carried out by the Energy Saving Trust on behalf of the Government prior to introducing the RHI (Renewable Heat Incentive) and against all my experience as an installer. No wonder the uptake of heat pumps has been well below the Government’s target given that the only document regarding energy efficiency that everyone has to have on purchasing or renting a home (with the exception of listed buildings) is so skewed against them.

When challenged the stock answer given by BRE is:

 “the reason that the heat demand may increase with a heat pump compared to an oil boiler, is that heat pumps … may need to be run for longer hours to give sufficient heat output over a 24 hour period and to avoid very long warm up times. Running longer hours…. would result in higher mean internal temperature. Consequently, the total heat losses would be higher, so the energy requirement would be higher” 4

This statement is simply inaccurate. Whether continuous or intermittent heating is more efficient is a highly contentious issue and depends on many factors including occupancy times and the insulation of the building. Frequently heating a building from cold – which intermittent heating requires – uses a great deal of energy particularly if that heat is delivered at a high temperature – as it is with an oil or gas boiler. A low temperature system such as a heat pump, running continuously, may well use less energy than a high temperature system running intermittently. Moreover, the fact that the heat pump obtains most of its energy free from the sun, mediated via the air or the ground, means that it will undoubtedly work out far cheaper to run than oil, direct electric or LPG.5

It seems odd, to say the least, that BRE should assume a heat pump will use more energy and even odder that, instead of  downgrading the efficiency of the pump – which is logically what they should do – they add the highly dubious up-lift in energy requirement to the heat loss of the building. This has the curious – and surely unintended – effect of increasing RHI payments to homeowners who have their EPC issued after rather than before the installation of a heat pump.6

This bias against heat pumps gets even worse when we look at another curious change in the 2017 SAP revision. The revised SAP (on which EPCs are based) attempts to work out whether the heat pump capacity is sufficient to meet the heat demand of the building by cross referencing the capacity of the pump, as specified in the Products Characteristics Database, with the heat loss of the building. If this calculation determines that the heat pump has insufficient capacity it assumes that the shortfall will be made up by the most expensive heating source of all – direct electric heaters – and adds the cost of this to the running costs of the heat pump! This assumption would be bad enough on its own, but the EPC software allows for only one heat pump to be entered into the data input of the EPC. However, where one pump cannot meet the heat demand of the building, installers must install 2 or more pumps (unless installing a hybrid system) – but this will only register as one pump in the software. So if 2 x 14kW pumps are installed, the EPC  will only recognise 1 x 14kW unit and assume that a large proportion of the heat demand of the property will be met by direct electric which vastly overestimates the cost of heating the dwelling using a heat pump even though the heat pump system (comprising 2 or more pumps) is perfectly capable of meeting the heat demand on its own.7

Even where only one pump is employed, the EPC is far too crude an instrument to determine whether the specified heat pump is capable of meeting heat demand. The MCS (Microgeneration Certification Scheme) calculation method, which is used to determine pump size by installers, employs much lengthier and more accurate measurements based on room by room heat losses. It is presumptuous to assume that the EPC is correct and then inflate the estimated running costs of the pump based on this presumption. At every stage in the process the revised SAP seems to assume the worst case for heat pumps and I believe this betrays an institutional bias within BRE against heat pumps. It really could not be any worse if the revised SAP had been produced by the fossil fuel lobby.8

I will now illustrate the complete inadequacy of EPCs to give homeowners accurate advice on the relative merits of using heat pumps and other renewables as opposed to non-renewable energy sources with reference to some examples. 9

Example 1

Edwardian rectory, detached, floor area 290m2. Solid walls with no insulation, suspended floors with no insulation. Double glazed and 150mm of loft insulation. Occupied by 2 adults and 2 children.

Prior to the installation of a Kensa 24kW GSHP (Ground Source Heat Pump), the property was heated by an oil boiler at a cost of £3500 per annum.10 The cost of using a GSHP predicted by current EPC software is £3600 (an earlier EPC from 2015 predicted £2908 pa). The actual cost for 2016, as recorded by the homeowner and supported by his bills, was £1511 per annum! Part of this dramatic reduction was due to the very low electricity tariff (9.2p/kWh) enjoyed by the homeowner, but even correcting for this the running costs would be substantially less than oil. I had calculated, using the MCS calculation tool and assuming electricity costs of 13p/kWh in 2015, annual running costs of £2350 – very close to what actual running costs would have been at this electricity cost rate. In kWh the MCS calculation estimated the heat pump would use 18,994kWh per annum. Meter readings from the customer showed usage from 9/12/2015 – 30/112016 was 16,420kWh – allowing for the 9 missing days the figures are very close.

The EPC recommended measure for this house was not a heat pump but a new oil boiler.  This is not an isolated example – all installations carried out by my company are showing running costs with heat pumps very close to or less than the predicted running costs using the MCS calculation tool, but completely at variance with EPCs based on the revised SAP.


Example 2

1970s detached house, floor area 133m2. Cavity walls with foam backed breeze blocks, solid floor, no insulation. Double glazed and 270mm of loft insulation. Occupied by retired couple.

Prior to installation of a Mitsubishi 8.5kW ASHP the property was heated by an LPG boiler at a cost of £2400 per annum.11 The EPC, produced following installation of the heat pump in 2013, predicted running costs for the pump of £1279 per annum. The MCS projected running costs were £1051 per annum. The actual running costs, as shown by the customer’s energy bills for the year following installation, were £508. The very low costs, even compared to the MCS prediction, can be partly attributed to the 4kW of solar PV (photovoltaic) installed at the same time which would account for most but not all the difference. However, this does illustrate another failing of the EPC which does not take into account the significant contribution to energy requirements of heat pumps which solar PV can make. This combination of solar PV + heat pump is an extremely powerful tool for reducing running costs and CO2 emissions. Considering that one of the prime functions of the EPC is to help homeowners reduce CO2 emissions it represents another major failing of the EPC.

Example 3

1990’s detached house, floor area 126m2. Cavity wall insulation, double glazed, 150mm of loft insulation. Solid floor with no insulation. Occupied by a retired couple.

Prior to the installation of an 8.5 kW Mitsubishi heat pump the property was heated by an oil boiler supplemented by some direct electric heating. The oil bill alone was close to £1000 per annum which is broadly in line with the estimate of £1045 per annum on the EPC issued shortly before the installation of the heat pump in August 2017. There is no doubt a new EPC based on the revised SAP showing the heat pump as the heat source would predict higher running costs. Energy usage estimated using the MCS calculation tool for the heat pump was 5317kWh per annum. Actual energy used by the heat pump was 4653kWh producing an energy bill of £651 per annum – a very significant saving over oil and much lower CO2 emissions.12

Example 4

Because of the very low price of natural gas compared to electricity it is generally assumed that a heat pump cannot compete on price alone with an efficient gas boiler. With electricity costing around 15p/kWh and natural gas less than 4p/kWh an SPF greater than 3.75 is needed for the heat pump running costs to be the same or cheaper than natural gas. However, even a modest solar PV system can tilt the balance in favour of heat pumps by providing some of the electricity input free. This combination has the advantage of dramatically reducing the carbon footprint of a dwelling. Consider this example:

1990’s detached bungalow, 177m2. Insulated sandstone walls, double glazed, 300mm loft insulation. Suspended floor, no insulation. Occupied by retired couple.

Prior to the installation of the heat pump the property was heated by a gas boiler less than 10 years old. A 4kW solar PV system had already been installed generating around 3300kWh per annum. The combined energy bill prior to the installation of solar and heat pump for 2014-2015 was £1551 pa. After installation of solar and heat pump the combined energy bill for 2015-2016 was £903.13 The saving of £648 was largely due to the reduction in electricity bill caused by the solar but the most that could be, assuming zero export of solar generation, is £462 leaving a further saving of £186 to be accounted for. Could it be that a low temperature heating system running continuously is more efficient and cheaper to run than a high temperature system running intermittently even when the latter is fueled by natural gas? I believe it is and I would further suggest that when a dwelling is heated continuously, residents tend to set the thermostat lower than when they are heating it intermittently – although I have only anecdotal evidence to support this (mainly from telephone conversations with customers) I am inclined to believe it is the case and is another possible argument in favour of continuous heating. This, of course, completely contradicts the assertion of BRE that continuous heating is less efficient and more expensive.

The above examples were not “cherry-picked” to support an argument. They were chosen because they are instances where we have access to reliable figures from customers’ bills and accurate record keeping rather than just verbal feed-back. In fact, all of them are “hard cases” for heat pumps because none of them are modern buildings built to good insulation standards – they are typical of current UK housing stock with poor to average insulation values.

It is widely assumed that heat pumps work better in well insulated houses and struggle in poorly insulated ones. All heating system run more efficiently and cost less to run in well insulated buildings, and this is not a factor that is unique to heat pumps. In fact, we find little correlation between how well insulated a dwelling is and the performance of the pump as long as the heat distribution system is sized correctly. By far the biggest influence on performance is user behaviour. Where customers have reported high bills, we invariably find it is in new buildings with underfloor heating and the cause is often traced to one room thermostat turned up to 23°C or more and all the windows open! The room cannot, of course, reach temperature and calls for heat constantly causing the heat pump to run continuously. This is down to customer education not the efficiency of the pump.

There are other factors which lead to poor heat pump performance. As servicing and repair engineers for several organisations, we come across many problems caused by poor design or installation of heat pump systems. These include – inadequate up-grading of the existing heat distribution system in retrofits, poor or non-existent control systems (even in new-builds), no three-port valve fitted, and many others. Most of these problems were identified by the 2013 study referred to above which gave detailed information on each system included in the study. That is why the conclusion of the study was careful to say that “correctly installed and operated heat pumps can perform to a very high standard in UK homes”. I strongly suspect that any data looked at by BRE in revising the SAP and subsequently the EPCs made no such allowances and is adulterated by the inclusion of very poor heat pump installations.

Whatever the case, the Government cannot continue to believe that the revised SAP is correct and also believe that the 2013 study (which is far more extensive and detailed than anything BRE have done) on which its own policies and the Renewable Heat Incentive are based, is also correct – they flatly contradict each other. The 2013 study is broadly in line with my experience as an installer and with all the studies carried out by heat pump manufacturers and the Ground Source Heat Pump Association.14

Professor David Mackay, who sadly died in 2016, was Chief Scientific Advisor at the Department of Energy & Climate Change (DECC) from 2009-2014. He was convinced that heat pumps were the way forward to reduce CO2 emissions in buildings. It is worth considering his remarks on heat pumps, which cannot be reconciled with assumptions underlying the revised SAP:

“Let me spell this out. Heat pumps are superior in efficiency to condensing boilers, even if the heat pumps are powered by electricity from a power station burning natural gas. If you want to heat lots of buildings using natural gas, you could install condensing boilers, which are “90% efficient,” or you could send the same gas to a new gas power station making electricity and install electricity-powered heat pumps in all the buildings; the second solution’s efficiency would be somewhere between 140% and 185%……..

My conclusion: can we reduce the energy we consume for heating? Yes. Can we get off fossil fuels at the same time? Yes……. Nay-sayers object that the coefficient of performance of air-source heat pumps is lousy – just 2 or 3. But their information is out of date. If we are careful to buy top-of-the-line heat pumps, we can do much better. The Japanese government legislated a decade-long efficiency drive that has greatly improved the performance of air-conditioners; thanks to this drive, there are now air-source heat pumps with a coefficient of performance of 4.9.” 15

BRE’s views on heat pumps and the revised SAP are out on a limb and completely at variance with every other informed assessment of heat pump performance.  The fact that BRE in effect determines the way heat pumps are assessed by EPCs is a case of the tail wagging the dog – the Government’s stated aims on heat pumps and the RHI cannot be reconciled with BRE’s views which have tremendous influence via EPCs.

Climate change has finally become top of the political agenda – even ahead, dare I say it, of Brexit. It is the most important issue of our time and we should be doing everything we can to encourage the uptake of renewable energy. As it stands, the EPC is a major obstacle to this and its assumptions, hidden in its algorithms, have to be challenged and changed.  EPCs should encourage the movement away from fossil fuel heating systems to renewable energy systems and especially promote the uptake of combinations of renewables – particularly the combination of heat pumps with solar PV. Considering we have a “climate emergency”, EPCs are currently not fit for purpose and need to be radically reformed if we are to meet our CO2 reduction targets.

Chris Wilde, MD
Yorkshire Energy Systems Ltd
Windsor House
Cornwall Road

t. 01423 529144
m. 07831543268

  1. Energy Saving Trust, The heat is on: heat pump trials: phase2, July 2013, 36
  2. Energy Saving Trust, Analysis od data from 23 Mitsubishi heat pumps, June 2013, Executive Summary
  3. This can be viewed online at:


  1. This response to my concerns is taken from a letter from Chris Skidmore, Minister for Energy and Clean Growth. It is almost word for word the same as I received from BEIS and originates from BRE. Government departments seem to be oblivious to the fact that the BRE view is completely at odds with their own stated policies.
  2. Natural gas is currently so cheap it is difficult to guarantee that a heat pump will be cheaper to run at current electricity prices, but it often is and would certainly be so with sufficient solar input – see Example 4.
  3. The Renewable Heat Incentive payments for domestic installations that are not hybrid are determined by the heating and hot water demand of the property estimated by the EPC and the SPF of the pump at the design flow temperature. The higher the heat demand the higher the payments up to the cap. In hybrid systems – where part of the heat demand is met by a heat pump, and part by an alternative source – the system must be metered for payment and RHI payments are determined by actual output of the pump, not deemed based on the EPC estimate.
  4. If the system is not hybrid the installer must guarantee that the heat pump can meet 100% of the building demand at the design temperature without secondary heating. In assuming that the heat pump can’t do this the EPC is in affect declaring that the pump is not eligible for the RHI – but this is not picked up. Installers must ensure that the heat pump can meet demand under MCS (Microgeneration Certification Scheme) regulations so there should be no assumption that it can’t – the amended SAP and the MCS regulations are in conflict with each other – again this displays a lack of joined up thinking in Government – officials are simply not aware of the conflicts created by the amended SAP.
  5. The wide variance in heat loss calculations between the EPC and the MCS calculation tool can also cause major problems with RHI applications. Applicants must submit an MCS Certificate showing the MCS heat loss calculation, together with the EPC which can be greatly at variance with each other if the EPC was produced after the installation of the heat pump. This often leads to delays or even refusal of RHI payments by Ofgem because of the disparity – a disparity that is inevitable since the EPC adds a third to the heat loss if a heat pump is the heat source. If accepted, the lucky applicant will receive much higher payments if the EPC is done after the heat pump installation than before because the RHI payments are based on the predicted energy required to be produced by the pump. This disparity in payments is surely a bizarre and unintended consequence of the EPC pushing up the heat loss of the building after a heat pump is installed.
  6. I have now instructed all our servicing engineers to collect energy input and output data and running costs from every pump at every service. This will provide an accurate database of SPFs and running costs for around 100 pumps over the next 6 months. In the meantime, the examples given represent typical performance figures as reported by our customers.
  7. Figures obtained from very detailed Excel document kept by the homeowner based on his bills and meter readings. I can make this and all other data available to interested parties on request.
  8. Figures obtained from energy bills sent to me by the homeowner.
  9. Figures obtained from detailed records kept by the homeowner including readings from the electrical input to and energy output from the pump.
  10. Figures emailed to me by the homeowner from his own analysis of his bills.
  11. https://www.gshp.org.uk/
  12. David J C Mackay, Sustainable Energy — without the hot air, Cambridge, 2009, pp. 146-153
Heatpumps EPCs flawed
Heatpumps EPCs flawed
Heatpumps EPCs flawed