@mike-patrick my understanding is that ashp should definitely be an improvement. But it maybe more than just a tickbox error. 

I think Assessors should use the exact make & model + MCS cert to get the details right. If they can't find your make/model etc they may use assumptions that are totally incorrect. The controls are also important. Preferably demonstrating using weather compensation. They still award points for thermostats/secondary controls even though most people say its best run 24x7 on open loop and weather compensation 

Have you contacted the assessor and asked for it to be re-checked? Offering evidence?

@mike-patrick maybe pickup this ChatGPT conversation and add more of your detailed setup etc. 

https://chatgpt.com/s/t_68e2b4c2120881919e6c7bd22e9688b5

I used it for mine by uploading previous EPCs, details of works, evidence etc

Thanks for this. ChatGPT has proved very helpful. It helped me identify that the problem with the EPC is probably down to just one word.

It rates the Heating system as, Air source heat pump, underfloor, electric. Whereas it should say wet. I've read this line many times but its significance never occured to me. I read electric as referring to the ASHP. But electric means the UFH heating consists of resistive electric wires, which have a far worse rating than "wet" which means the ASHP circulates coolant through pipework (as mine does). I'm not sure why anyone with an ASHP would have electric UFH, but there we go.

The energy assessor is no longer in business so I'm going to revert to Elmhurst Energy and see if I can get a re-rating on the basis of this. I now feel stupid for not having spotted it before over the last 8 years. I've always had a nagging feeling that something was wrong but have never been able to get to the bottom of it. But, on the other hand, I'm the end-user retail customer. Should I really be expected to be this technically aware of how the EPC algorithm works?  If getting a car MOT was like this we'd all be going crazy.

Lesson learned, for me, is that we have to treat EPC assessors with the same degree of caution as we do the ASHP installers. What an industry! It seems to be populated with a lot of people running around with paper qualifications that provide no assurance of skill or ability in their subject.

I'll post again on this when I have had a response from Elmhurst.

Many thanks,

Mike

@mike-patrick good find Mike! Very much agree with your comments 

If the EPC is old it might be simpler to get a new one? Especially capturing latest RdSAP10 ... and making sure you choose an assessor that will do the detailed work and use proper proofs etc? 

May be worth asking around locally via estate agents, Facebook etc for recommendations.

BTW did ChatGPT suggest how many points improvement you should see for that alone?

Tim,

Yes ChatGPT thought I could get another 10 points just for that change. That would get me over the line to a C.

Mike

Two steps forward and one back. A further "conversation" with ChatGPT contradicted some information in the first one and I am now back to reviewing the scoring algorithm  behind the EPC. Elmhurst Energy said that there was nothing wrong with how the data had been entered for my EPC.

Where I am at now is:

The main heating on our EPC is described as ASHP, underfloor electric and apparently that is correct. It is assessed as "Poor"

The previous EPC, from before our refurb rated the then Storage Heaters as "Average", apparently because the assumption is that they run off overnight cheap rate electricity. (which I still have)

I've seen EPCs of houses with mains gas boiler powered UFH (oh, those were the days) that rate the gas boiler as "Good"

So my ASHP is rated worse than both older technologies!

I was talking with a friend about my travails and he said, oh I have an ASHP and it's rated Very Good. What's more the EPC overall is A 100. Wow.

What is going on? I found his EPC online (see attached). The big difference is that the assessment was a SAP one (from 2020), not RdSAP (from 2017). It rates a number of features that don't appear on my shorter certificate. It looks like the SAP assessment enables more specific details about a property to be recorded, whereas the RdSAP makes general assumptions that may be less favourable.

For example the description of the heat pump says a lot more - ASHP, Underfloor heating, pipes in screed above insulation, electric. That is exactly the same as my installation except the EPC omits the additional wording about the pipes. My friend clearly also had the actual thermal performance of the walls  and the overall air tightness tested.

So back to Elmhurst Energy to find out if a SAP assessment, instead of an RdSAP one is likely to produce a better rating. It will no doubt cost more.

It is like getting blood out of a stone talking to people in this industry.

Mike

Extract from my friends A 100 rated EPC. His house, like mine is a mixture of old and new build

@mike-patrick I'm no expert... but believe your ASHP is incorrectly rated under all scenarios! 

Possibly they failed to find the make/model in their system and used an incorrect placeholder.

My understanding...

SAP is used for new builds: The full SAP assessment is required for all new domestic dwellings, as well as for conversions and extensions.

Used for existing homes: A simplified version of the methodology called Reduced Data Standard Assessment Procedure (RdSAP) is used for existing dwellings.

So it's quite possible your works etc should be under SAP?

I suggest try asking Assessors for a quote to do SAP assessment based on evidence etc. Hopefully around £80?

Just returning to this issue after a few days working in Riyadh. Lots of heat pumps there but for aircon rather than heating! Petrol is about 40 pence per litre and electric cars rare (apparently because the EV batteries can overheat and even catch fire in the summer). Lots of gas guzzlers on the roads.

But I digress.

Elmhurst Energy said the SAP assessment was for new builds, which mine is not. My research says that SAP (rather than RdSAP) can also be used for existing buildings with major renovations. Mine was a 30% increase in the floor area which I call a major renovation.

I've pointed this out to Elmhurst. I'm not sure whether they don't know the rules, don't understand them or just don't want to tell anyone like me who starts asking awkward questions.

From a consumer perspective there is a lack of transparency in this industry and an apparent unwillingness to improve it. Keeping consumers in the dark is not a recipe for improving the products and gaining widespread acceptance of them.

Mike

@mike-patrick Michael De Podesta https://protonsforbreakfast.wordpress.com/2025/09/18/epc-fun-5-the-aftermath/ has had extensive ‘fun’ with EPCs. He eventually got the basic mistake of rating an Ashp as ‘poor electric heating’ changed. But it took him some considerable time to and energy to get the change but generated considerable media attention in the process.

Posted by: @mike-patrick

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The energy assessor is no longer in business so I'm going to revert to Elmhurst Energy

As I understand the situation, Elmhurst Energy trains energy assessors and provides them with accreditation.
Although they are basing their work on the regulations, they are an independent operation, and can supplement their training with additional guidelines.

Elmhurst do not offer their own energy surveys.
Their reputation relies on the accuracy and attention to detail which their 'members' apply.

Posted by: @mike-patrick

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Elmhurst Energy said the SAP assessment was for new builds, which mine is not. My research says that SAP (rather than RdSAP) can also be used for existing buildings with major renovations.

I largely agree with that explanation.

Not all Energy Surveyors would be prepared to offer a SAP or RdSAP.
There's a hefty annual fee to have use of the SAP software, and it's not a pre-requisite for conducting Energy Assessments.

I have discussed SAP with a qualified Building Control Inspector/Surveyor.

He states that SAP is more comprehensive than a standard EPC, and includes a great many points that aren't directly related to energy.
These include whether the house has a home-office/study, or a bike-shed, for example.

When the Assessor enters details into the SAP software it offers the option to print out a multi-page form which contains all those entries.
Thus, if the householder believes that the EPC report which has been created from SAP Software is flawed, they can ask the Assessor for the full output.
A homeowner can then read through every section and check if data has been inaccurately entered.

The other advantage of obtaining the multi-page output is that each page bears the version number of the SAP software which was used,
and the licence number of that Assessor. Check if that matches what you expect to see.

The large housebuilding firms who are members of NHBC often use a loophole whereby their newbuilds are given SAP scores (and hence EPCs) which do not reflect the current standards.

When they first 'register the site' with NHBC, the clock effectively stops for both the version of SAP which be applied, and the Building Control version which they will build to.

Thus a site of some 400-dwellings being built by Bovis-Homes near to me is still under construction,
but the site was 'registered' in 2015, before they had even purchased the land.

The estate is therefore built to the 2006 edition of the Building Regulations Approved Documents, and the 2012 SAP software.
New homeowners are unaware of this. They are supplied with the EPC rating, without realising that it has been derived from less-stringent regulatory standards.
Only if they requested the full SAP printout would they be able to see that information.

@judith This is very interesting. I've located and printed out Michael De Podesta's latest "A" rated EPC to compare it with my own "D" rated one.

Both are done to the RdSAP standard. There appear to be glaring inconsistencies.

His glazing is rated Average, mine is Good.

His ASHP, radiators, electric is rated Good. My ASHP, underfloor, electric is rated Poor.

Now the wording for the description of each feature has a specific meaning, depending on the assessors input. Without access, as the customer, to a glossary that explains the link between the input and the resulting description it's impossible to know whether the input accurately reflects the actual observed feature in the property.

I'm going to continue to press Elmhurst Energy (the  government website says to do this if the assessor is no longer an assessor) for an explanation (so far all I have got is stonewalling) but having read Michael De Posta's blog I see that it will probably prove to be an uphill struggle.

Mike

Another glaring problem with RDSAP10 is that assessors will not investigate; for example Cavity Wall Insulation, despite my offer to drill holes for him wherever he wanted and use my boroscope!  Instead, they discount it.