There is  a real disconnect between how performance is captured for RHI and what ends up being used for EPCs via RDSAP.

The SPF of 4.1 you got  probably reflects the real-world performance of your GSHP. But RDSAP, being a cut-down version of the full SAP methodology, often uses default or oversimplified figures—hence that laughable COP of 1.7. That number doesn’t reflect the capabilities of a modern MCS-certified system like MCS HP0016/08, especially if it’s been properly designed and commissioned.

To improve the EPC rating and get a COP/SCOP that reflects reality (especially at 40°C flow temp), you ideally want to use the Product Characteristics Database (PCDB). If your heat pump is listed in there, SAP can pull in the correct performance figures. If not, RDSAP defaults will drag the rating down every time.

And no—SPF and COP aren’t interchangeable. SPF takes into account the whole system and how it behaves across seasons, whereas COP/SCOP is a performance figure under fixed conditions. Related, yes. Swappable? No.

Honestly, if you’re aiming to push the rating from a D to a C and you’ve already got detailed performance data from the RHI assessment, it’s far better to do a full SAP. It’s more work and takes longer, but it allows you to input all the real data properly—emitters, controls, flow temps, measured demand, and system design. That’s where you stand a decent chance of getting the rating

@aaron  There's the rub, the database does not list my HP, it appears to begin in 2016. So does this mean we cannot get a COP figure at all?  https://www.ncm-pcdb.org.uk/sap/pcdbsearch.jsp?heatPumpType=1&emitterType=3&type=362&serviceProvision=1&brand=&model=&modelQualifier=&pid=31

No Bosch or IVT GSHPs listed.

With the change to RdSAP in June I have just followed up with an EPC assessor to ask if it would make a difference to get our house re-rated. We have an overall rating of D, despite having done everything 8 years ago when the ASHP was installed. He was familiar with the problem of ASHPs resulting in worse ratings than a gas boiler in an identical property. Unfortunately his message was that the new RdSAP will make no difference and might even give a worse result. It's down to the model and he said his firm now gives warnings in advance to customers that their EPC rating will likely not have improved despite spending £000's on an ASHP installation. He said, we only collect the data, the rating is down to the underlying model.

We all know this to be true but strange how no one from government or those groups pushing heat pumps ever seem to mention this inconvenient detail.

For now I will sit tight and hope for future changes to RdSAP that tip the balance in favour of heat pumps.

Mike

@mike-patrick interesting!

Funnily enough we've just arranged a new EPC even though current one was done 5 years ago. Both for my property and one belonging to my son.

Current one was pre our heat pump or added solar & batteries. Our assessor indicated the heat pump WILL improve matters. I'll report back once epc ratings received in coming days. Assessor was chosen for willingness to engage and do thorough assessment. Over 1.5 hours each property.

Also noting

• 2020 epc was done go get RHI with little effort to prove insulation etc. Both properties a D 67 & 68 points
• 2025 epc I've provided building regs Certs for extensions etc, mcs Certs for heat pump & solar panels  pics of insulation, receipts etc
• Assessor indicated batteries would not add more than solar already added. However he took details and promised to check that point.
• I'm moderately hopeful we'll get both to a C. Obviously useful target for potential lettings as well as sales.
• I used ChatGpt to get inputs on what changes have happened 2020-2025. I uploaded existing epc and details of all changes since. ChatGpt suggested both will be likely to achieve C

My understanding is that the next EPC update will be a change to HEM. Plan is for:

Our circumstances were slightly different in that the current EPC was issued after a ground up restoration of a semi-derelict building. We'd had a full MCS survey to receive the RHI grant at the time. So after all that and a £300k spend (inc underfloor heating) I was more than a little disappointed to get a D 62 rating with advice that I could reach C 69 by additionally installing solar hot water and solar PV.  Even if that were so it wouldn't have changed the fact that the certificate assessed the main heating and hot water as Poor. The house is 100% electric as there is no gas supply in our area.

I've done no further work on the house since, so my conversation with the assessor was about whether or not the latest RdSAP would result in an improved rating - which apparently it would not. Once the HEM is introduced I'll try again. I won't do solar panels - although I have consent for them. They'd not look great in our Cotswold village and I think the payback period on the capex is too long.

Mike

@mike-patrick Hi, I found that the previous EPC assessor had used a very low "Default efficiency value" for our "poor" GSHP. I got in touch with Bosch who found the correct figure which the RDSAP10 assessor used and it jumped from D to C.

@mike-patrick fo you use ChatGPT? Could be worth a conversation!! Upload your current epc as well as details of previous works and heat pump etc. Plus heat pump controls as they impact it too.

Maybe start here

https://chatgpt.com/s/t_68db8489b4108191a4237450ec358b98

I wonder if the original epc in fact did not take into account some of your works correctly?

My understanding from both my assessor and ChatGPT is that a Heat pump will make  difference to New EPCs. But I'll update once mine arrives!

ChatGPT says Rule of thumb:

A correctly documented ASHP installation (with weather compensation and thermostatic controls) is typically worth at least a band jump (5–10 points) if the house was previously gas-heated, and more if replacing direct electric.

This is interesting.

Attached is the page from my EPC which shows the Poor rating of the Main Heating and Hot Water. You've prompted me to look at the same page from the EPC from when we bought the house and before the retoration. Overall it had an F rating but the important point was that it had storage heaters and used an immersion heater for hot water. On the old certificate these were both rated Average! Storage heaters better than an ASHP - that can't be correct?

So maybe some wrong boxes were ticked when the EPC survey was done. It was the same assessor in both cases although having checked I find they are no longer an assessor. Is it possible to access the detailed report which shows what data went into an EPC to check this?

Mike

@mike-patrick  I think at the time of your EPC the heat pump would have come out badly - but things have changed since then. So maybe less a case of box ticking incorrectly... more the changes in calcs.

The controls will help on new EPC as well especially if you use weather compensation and have Thermostats/TRVS (even if unused).

I'm not sure if your underfloor insulation should show as a rating help? But may need evidence? e.g. receipts, pics etc

It needs an assessor willing to spend a bit of time on the survey as well as completion of the modelling. 

I have a couple of rentals. 

One was rated an E in 2021 but I had done a massive refurbishment. So after some toing and froing with assessor 2 or 3 years later and paying a further fee .. we got it to a C! Mostly by providing evidence.

In another example we had a new build in 2013 that was rated A. We needed a new EPC this year to relet. I expected a drop to B due to changes in standards. But came back as A again.

So I can only encourage you to persevere... ask around for a decent assessor via estate agents? Facebook? .... I think my hard working guy cost £10 more than a cheap one! Well worth it.

I am unaware you can access the data input by assessor.

From my understanding..

The short version

• Before June 2022 (SAP 2012 rules) → Heat pumps often hurt EPC scores compared to mains gas.

• Since June 2022 (SAP 10.2 rules) → Heat pumps generally help EPC scores, especially if fitted with weather compensation and thermostatic controls.

So, when exactly?

• Any EPC lodged before 15 June 2022 used SAP 2012 → heat pumps rarely improved the score vs. gas.

• Any EPC lodged on or after 15 June 2022 uses SAP 10.2 → heat pumps usually improve the score by +5 to +12 points vs. a gas boiler.

How many times and dates have epc sap rules been changed?

Here's the EPC printout to illustrate the point I made in a post last week. Sorry to keep banging on about this - but it is bonkers.

On the left the property's ratings before a total renovation when it had storage heaters. (Overall G)

On the right the EPC rating of the features in my house after the heat pump was installed. (Overall D)

The overall EPC rating had improved but not, apparently, because of the heat pump.

I still can't get to the bottom of whether this is just a "feature" of the EPC algorithm or the assessor ticking a wrong box when entering the data about the property.

Mike