Case Study 2 - 1950s Terrace House - 43E to a C (without CWI)

At the time of writing the methodology for EPC assessments of existing dwellings is RDSAP 9.94. The much anticipated RDSAP 10 update has not happened yet and a significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed for 2026.

This is the house I live in, and it's of the same design as the properties in Case Studies 1 and 3.

We bought this propery at auction in 2014, and the EPC rating was 43E. That EPC is about to expire because it's now 10 years old. We renovated the property during 2015 and 2016, and we want to improve the EPC rating further if we can, into the C band, by spending as little further money as possible.

Let's see what we can do.

Looking at our existing EPC issued in 2014, here is the Features table:

This information is a bit out of date now. Let's review where we are currently:

Wall - This is still a cavity wall without any insulation. We don't currently intend to fill the cavity due to cost. We have concrete Finlock guttering on the house and because this is prone to leaking and letting water pass down the cavity, we need to have the guttering cut off and replaced with UPVC before we have the cavity filled. It's possible I might tackle this myself with help from a builder neighbour at some point but for now we'll leave it as it is. The gutterring has had a glass fibre liner previously fitted which reduces the risk of water leakage for the time being.

Roof - The energy assessor states there is 50mm loft insulation. They got this completely wrong. In fact, 250mm loft insulation was present at the time this EPC was issued and an installation certificate was present in the loft detailing this. However, we have since fitted loft legs and boards in the loft, and have compressed the insulation slightly and can only declare 200mm now. It's still an improvement on the 50mm declared previously though, and because it is above 150mm, there will no longer be a related recomendation in a new EPC to increase the depth. Interestingly, on our Loft Insulation page, we describe how increasing the depth will not improve the EPC rating for this particular property.

Window - We still have these same double glazed windows, as before, with aluminium thermal spacer bars. We plan to leave these as they are because there isn't really any real benefit to replacing them with new from an EPC rating perspective for this particular property. When RDSAP10 is introduced it will be possible to declare double glazing fitted from 2023 onwards but at the moment it is not and the cost of replacing them would be significant.

Main Heating - This is where we have made a big difference. The property had a limited number of storage heaters as the main source of heating. The heaters were not present in all habitable rooms, resulting in the Secondary Heating entry in this table (see below). We replaced the storage heaters in 2016 with a full gas central heating system, and this single change has made the greatest difference to the EPC rating. The boiler we have is a pretty modern gas condensing combi boiler - it's an Alpha Intec2 28X. We'll come back to this boiler in a moment...

Main Heating Control - Now that we have a modern gas combi boiler running radiators in all habitable rooms in the property, in terms of heating controls we have the best set of 'standard controls', consisting of: TRVs (required on at least 50% of the rads), Programmer and a standard Thermostat. We'll come back to Heating Controls in a moment....

Hot Water - Previously provided by an electric immersion heater, this now comes from the gas combi boiler instead - this is a far cheaper way of heating water compared to the electric immersion heater we had before.

Lighting - We now have LEDs in all light fittings. This only makes a small difference, likely just 1 SAP point improvement to the EPC rating.

Floor - This is still a solid floor. We do not intend digging it out and putting solid floor insulation in place due to the cost, effort and low return in terms of EPC rating increase.

Secondary Heating - Here it lists: "Portable electric heaters (assumed)". This is an importat signal to recognise if you have this on your EPC. This was created by the RDSAP system automatically, most likely due to one or more habitable rooms in the property not having a source of space heating present. RDSAP assumes that portable (peak rate) electric heaters will be used to fill the heating shortfall of the property. That is a costly fuel, and for electric heaters it assumes they will be used for 20% of the floor area of the property. If you have this listed, but you also have a central heating system using a cheaper fuel such as mains gas, it will ordinarily reduce the EPC rating of your property significantly. This doesn't apply however when storage heaters are the main source of heating. Following the work already carred out on the house, we now have a gas combi boiler, all habitable rooms are heated, and we have no forms of secondary heating present, so when we have the EPC conducted again there will be no form of secondary heating declared either manually or assumed by RDSAP, and we know that our rating will not be cut down.

So, we want to improve our EPC rating to a C if possible as that's a bit of a Holy Grail for older properties, and we'd like to see if that's possible without Cavity Wall Insulation, and by spending as litle money as possible.

The new Labour government of 2024 has indicated the MEES requirements for rental properties will be raised to a C rating for new tenancies from 2028 and existing tenancies by 2030, and a new EPC format will be introduced by then with multiple ratings metrics. Although we don't intend to rent out thie property, a C rating would look atttractive to a future buyer if we eventually sell the property within the next 10 years.

Next we run a Home Energy Report, which is just like an EPC, but without the formal lodgement process at the end. We do this to find the current rating of our house, and use it as a baseline to work out what we can do to improve it further.

At the time, it also meant that for the time being without a newer EPC being lodged we still keep our old E band EPC in case we might be able to claim under a scheme for some insulation in the future (often a D or lower rating is required to qualify for such schemes). In reality there were only a few months left to run on the existing EPC and that has since expired.

During the assessment, I had to make a change to our electric feature log burner that we now have in the lounge. We only use the illuminaton feature of this device, and never use it for heating. It sits as a focal point in the old fireplace, but it was wired into a switched fused spur, likely making it 'fixed' and therefore declarable for EPC purposes. This would have been recorded in the assessment as a form of 'Secondary Heating'.

I fitted a trailing socket and an in-line plug in the cable to make absolutely sure it could be viewed as being a portable heater. It is therefore disregarded during an EPC assessment.

See our page about Heating Systems to see what effect this electric heater could have had on the EPC rating when the main source of heating in a property is a gas boiler.

So the rating has come out at a 68D. That's just one point short of being in the C band. We need to get at least one more point from somewhere. How can we do that, and can we do it cheaply?

After some checking in the RDSAP software here are some options:

If I had the money, I'd probably choose to re-batton and re-felt the roof, have the Finlock guttering cut off and replaced with UPVC and have CWI installed and Solar PV.

We're looking to keep the costs as low as possible though, and after some extended thought, there are two avenues we are persuing, and they could provide an improvement of one SAP point each.

The first approach is to upgrade the heating controls on the boiler to some form of Compensating controller rather than the existing ON/OFF controller.

The other is that if we can record evidence of the age of the heating pump, and if this pump complies with the newer ErP energy efficiency legislation we can declare it's age as '2013 or later'.

These are the measures we are persuing for now, but the last option in the list for Time & Temperature Zone Control would be the next item in line for implementation. This could be achieved with smart TRVs and might only cost a couple of hundred pounds. See our Heating Controls page for more information. 

Our boiler is a gas combi and the heating pump is located within the casing, out of view from any passing Domestic Energy Assessor. In the absence of any documentary evidence, an energy assessor would declare the age of that heating pump as 'Unknown'.

If we can confirm the pump qualifies as being aged 2013 or later, and we also gather documentary evidence (ideally digital photographs with geo-location tagging in the meta-data), then I think most energy assessors and EPC auditors would be happy to accept that declaration.

Any modern smartphone should be sufficient. The geo-location data is likely to satisfy the curiosity of any EPC auditer - EPCs are occasionally audited for quality control.

We will take a close up photo and a couple of mid-field photos showing the location context of the boiler.

I forgot to take these photos when we had the boiler serviced in March 2024 so I'll have to wait until the next service to do that cost effectively. I'm not GasSafe registered so I'm not supposed to take the boiler cover off myself.

We're pretty convinced the heating pump will be dated '2013 or later' because the boiler was fitted brand new in 2015/2016 and we'd expect the components to be similarly dated.

See our Heating Pump Age page for more information.

When we had the Alpha boiler fitted in 2015, I remember Mark the heating engineer offering us a choice of controller to supply with it.

There was a range from a very simple timer, all the way up to the Alpha Climatic Controller which had lots of dials and buttons.

We chose the Alpha Digistat partly to make things straightforward but largely because it was towards the lower end of the cost range.

Having now become much more interested in energy assessment, and boiler efficiency, and EPC ratings, I found myself revisiting this choice of controls, and recalling that day when Mark showed me the brochure.

Researchig online, I discovered that our boiler is not OpenTherm compliant, and only has a proprietry Alpha BUS interface for connecting advanced heating controls. We were therefore limited to purchasing an Alpha branded control.

After more research, I bought a second hand Alpha Weather Compensation Sensor on eBay for £28 and a second hand Alpha Climatic Controller on Gumtree for £65.

These provide modulation of the water flow temperature of the boiler based on two things:

• Load Compensation – considering the difference between the actual room temperature and the target room temperature
• Weather compensation – similarly considering the temperature outside the house compared to inside the house.

For further information, see our Heating Controls page.

The main noticeable effect is that the boiler runs with lower temperature water running through the radiators. This ensures the boiler operates as much as possible in condensing mode. Also, as the room approaches the target temperature, the boiler reduces the flow temperature further so that the room does not overshoot the target temperature. The boiler operates for longer but at a lower load and should not fire on an off so much as it would have done with the previous controls. These things make the boiler operate slightly more efficiently than before, and this can be reflected in the EPC rating.

Similarly, due to the weather compensation sensor, in the winter when the temperature outside is cold, the boiler will raise the flow temperature of the water to compensate for the additional heat being lost through the walls of the house. Otherwise it keeps the temperature lower when not required. There is a control to adjust the 'Weather Compensation Curve' to match the energy loss of our house.

We had these devices fitted at the last boiler service in March 2024 and I'm really happy with them.

Then it came to getting them recognised in the RDSAP software however, and that's where we hit a problem.

I use the RDSAP GO app from Elmhurst to conduct assessments for EPCs and Home Energy Reports. It's quickly evident you can only assign one or other of these products to the boiler, not both of them at the same time.

Additionally, if I try and assign either of them to the boiler, the software raises an error. A quick call to Elmhurst technical support didn't give me any further information other than confirming it was an issue within the Product Characteristics Database (PCDB / PCDF), which is the external database that holds information about boilers and compensation controllers. The EPC assessment draws information in from this database about your boiler etc for use in the overall rating calculation.

In the end, I was able to identify the cause of the problem from my own investigation.

Our boiler, the Alpha Intec2 28X is listed in the PCDB. Also, the Alpha weather compensation sensor, and the Alpha Climatic Controller are also both listed in the PCDB.

The problem is that the Intec2 28X is not present in the list of 'Compatible Boilers' held against either the weather sensor or the climatic controller in the PCDB.

Other Alpha boilers are present in those compatibility lists, and if I select one of those boilers and assign the climatic controller, it succeeds, and we get one additional SAP point on the EPC rating for our property.

For our boiler, the Intec2 28X though, we are currently stuck.

I've written more about this on our Resolve PCDB Issues page.

I emailed Alpha to make them aware of this technical issue, and those initial emails were ignored by the frontline staff. I then wrote to Alpha and they did then engage and assign a product engineer to help. They contacted the Building Research Establishment (BRE) who host the PCDB, cc'ing me in on the emails, and the BRE have been absolutely rubbish - they have not responded at all. Unfortunatley, my contact at Alpha has now left the company and I have written to Alpha again to see if they would be willing to assign another product engineer to chase the BRE. After a further 4 months I looked up the company on Companies House website, located the list of directors, and wrote directly to the Financial Director. I've not heard anything. I'll write to the Managing Director next.

At the moment we're not able to claim any additional benefit towards the EPC rating from the climatic controller, and I'm waiting until the next boiler service to take photos to confirm the heating pump age.

The other cost effective option for us would be to fit qualifiying Smart TRVs and claim Time & Temperature Zone controls. For this I would probably look towards a product such as the TP-Link Kasa system:

Further information is available on our Heating Controls page.

We've decided however to leave things as they are for now because of the trouble we've experienced with the climatic controller, and we've realied that currently having a D rated EPC might qualify us for a cavity wall insulation grant in the future - although we have not researched that yet.

I'll post an update when we make further progress.

In the meantime, go back to our main Case Studies page and see if you an find any further inspiration