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

At the time of writing this page, the methodology for EPC assessments of existing dwellings is RDSAP 10. A significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed for 2027 along with a restructuring of EPC metrics. Approaches to EPC rating improvement will therefore change further in the future.

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

It is a 1950s 3-bed terraced house which we bought at auction in 2014 and at the time the EPC rating was 43E.

EPCs are valid for 10 years, and this one eventually expired in 2024.

After purchasing the property, we renovated it over two years, and the most significant improvement was to provide a gas supply and install a gas central heating system.

We would like 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.

Here is the Features table from the 2014 EPC:

When we reviewed the situation in 2024, this information was a bit out of date, so let's check through these features and see what had already been improved:

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 into 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 stapled to one of the rafters. 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 beyond 200mm will not improve the EPC rating for this particular property when implemented as a single improvement measure.

Windows - We still have the same double glazed windows. They have aluminium spacer bars and we cannot confirm the installation date. They are recorded with an unknown glazing age, which is effectively 'pre-2002'. We plan to leave these as they are because the cost of replacing them would be significant (I'm guessing ~£3-4,000) and the EPC rating gain would be minimal.

Main Heating - This is where we have made a big change during our renovations. The property had a small 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 affected.

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.

Sometimes over the years, small changes occur to the EPC methodology to make it more accurate.

By running a fresh assessment now, we can find our current baseline rating, and can rely on any of the Recommendations that it may contain.

This also provides a reliable position to work from when choosing additional measures to implement going forwards.

During the assessment, I altered the wiring to our electric feature log burner in the lounge. 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 in an assessment. This would have been recorded as a form of 'Secondary Heating' and factored into the calculations even though we don't use it for 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 the EPC assessment.

See our page about Heating Systems to learn the effect electric heaters have on EPC ratings when the main source of heating in a property is a gas boiler.

So the rating has come out as a 68D.

For those that are interested, the update from RDSP 9.94 to RDSAP 10 on the 15th June 2025 made no difference to the rating. 

68D is just one point short of being in the C band, so we would really like to get at least one more point from somewhere.

How can we do that, and can we do it cheaply?

The Recommendations listed on this report, with the resulting incremental EPC ratings are:

With the cavity wall insulation we're going to leave that for now for the reasons mentioned earlier.

So too for the solid floor insulation. The effort required would be significant.

Solar Thermal just doesn't provide a large enough return for us, based on the financial investment required.

Solar PV however is something we would be interested in because it returns a decent improvement based on the financial investment. However, we would like to have our roof re-battoned and re-felted before installing, so we're going to leave this option for the time being also.

The headline rating on EPC certificates is displayed as an integer value, and our new baseline is 68D.

We want to gain 1 more SAP point because a rating of 69 would fall in the C band.

Behind the scenes though, the rating is actually calculated to 4 decimal places before finally being rounded to the nearest integer.

Where a number has a decimal component of 0.0001 to 0.4999 it is rounded down to the integer below.

Where a number has a decimal component of 0.5000 to 0.9999 it is rounded up to the integer above.

Sometimes an improvement measure might only increase the rating by a fraction of a point, and not be sufficient to roll the rating up to the next integer.

Multiple measures can however be combined together to do so.

Bear in mind standard EPC Recommendations will only appear if they improve the rating by at least one SAP point, or 0.5 in the case of LED lighting or hot water cylinder insulation.

There are also other changes that can improve an EPC rating which do not have corresponding recommendations available in the methodology.

In the following table we show ratings with their full decimal value so you can see what contribution each measure would make for this particular property.

Our current rating is actually 67.8978

To become a 69 this needs to be at least 68.5000

We therefore need to raise the rating by 68.500 - 67.8978 = 0.6022 SAP points.

Any single measure or a combination of measures that increases the rating by this value will get us the 69C.

Here are some changes that we've modelled in the assessment software, for this particular property:

When you implement multiple measures together, sometimes the rating improvements for each add up together as you might expect. Sometimes they work together to provide an even better improvement, and sometimes you simply don't get them effectively summing together.

It's therefore important to model combinations of improvement measures in the assessment software, so you know the outcome in advance, before proceeding.

There are five measures that interest me the most due perhaps to opportunity or low cost:

1. Load / Weather Compensating Heating Controls (+0.7712)
2. Heating Pump Age Confirmation - 2013+ (+0.4439)
3. Change the electricity tariff from dual rate to single rate (+0.1756)
4. Waste Water Heat Recovery - Recoup Easyfit+ (+0.5461)
5. Time & Temperature Zone Control (+1.4228)

We'll talk through each of these in a moment.

Just before that though, I want to highlight from the table above:

• Changing the mixer shower to an electric shower would bring the rating for this property down by 2.4 points. Do you have a gas boiler, either a combi or a system boiler with a hot water cylinder, but also have an electric shower? If so, ask your energy assessor what might happen to the rating if you swapped the shower out for a mixer shower.
• Many people on social media will automatically suggest putting more insulation in the loft as a measure to increase your EPC rating. Notice how doubling the loft insulation for this property from 200mm to 400mm only increases the rating by 0.3 points. If I had proceeded with this type of measure without knowing the outcome in advance, I would have been disapointed, and the time and money wasted if this was implemented as a single measure.
• Similarly, many people on social media will automatically suggest replacing your windows with new double glazing, even triple glazing, as a measure to increase your EPC rating. For this property if I had replaced all 10 windows with new double glazing the rating would only improve by 1.02 points. This would have got me the 69C I wanted but at a cost of perhaps up to £4,000.
• Air Pressure Test Result. Entering an air pressure test result for an EPC assessment of an existing dwelling has only been available as an option since 15th June 2025. Again many people on social media express a multiple point increase in EPC rating from entering such a result. For this property, we would only get a 0.65 point increase with a 6m3/hr/m2 test result.

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', and a small opportunity will have disappeared.

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, and this gives us a small increase in rating (see the table above).

Usefully, this measure costs nothing, assuming we take the photos during a regular boiler service.

Any modern smartphone should be sufficient to take the required photographic evidence, so long as location services are enabled.

A GasSafe registered competent person should remove the boiler cover to allow you to take the required photos.

We will take a close up photo and a couple of mid-field photos showing clear location context of the boiler. We can then take further photos on the day of the full assessment which match the location context of the photos of the boiler with it's cover off.

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 asking us to choose a controller for it.

Alpha's range of controls started with a very simple timer, and included products all the way up to the Climatic Controller which had lots of dials and buttons.

At the time, 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, boiler efficiency, and EPC ratings, I found myself revisiting this choice of controls, and recalling that day when Mark showed us the brochure.

Researchig online, I discovered 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 to get the best performance.

I bought a secondhand Alpha Weather Compensation Sensor on eBay for £28 and a secondhand 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 about this, see our Heating Controls page.

The main noticeable effect is 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 and 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 is 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.

When considering devices such as these, it is important to follow the guidance of your energy assessor. The device you choose needs to be listed in the Product Characteristics Database (PCDB).

We had these devices fitted at the 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 was actually aware of this problem before purchasing the controls, but I proceeded anyway.

These devices should provide us with a rating improvement of 0.7712 SAP points and take us to a 69C in a single measure.

At the time, I used the RDSAP GO app from Elmhurst to conduct assessments for EPCs and Home Energy Reports. It was evident I could only assign one or other of these products to the boiler, not both of them at the same time.

More importantly though, if I tried to assign either of them to the boiler, the software raised an error.

A quick call to Elmhurst technical support didn't provide any further information other than confirming it was an issue within the Product Characteristics Database (PCDB), which is the external database holding 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 research.

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.

I've written more about this on our Resolve PCDB Issues page including my efforts to try and get Alpha Therm to fix this issue, with zero success.

We are officially stuck with this improvement now, although I've obtained the corresponding value for the table above via an alternative software solution - enquiries pending about the validity of that path.

We currently have a dual rate electricity tariff due to the old storage heaters we removed in 2015.

We have no significant need for dual rate electricity these days, having had the gas boiler fitted, but we chose to stay with it anyway.

By changing to a single rate tariff our EPC rating will rise by a small amount: 0.1756 points.

This would not cost us anything to implement, and can be implemented in conjunction with other measures.

There are some systems that expect to have a dual rate electricity supply so looking at things from a different direction, if you have storage heaters in your home, or a hot water cylinder with dual immersion heaters but you are on a single rate electricty supply, ask your asessor what would happen to your rating if you moved to a dual-rate electricity supply.

Time & Temperature Zone Control (TTZC) is the ability to control programming times and target temperatures separately for two or more zones in a dwelling.

If we can qualify for TTZC it will increase the EPC rating of this property by 1.4228 points, and take us to our desired rating of 69C as a single measure.

TTZC can be achieved either with multiple physical plumbing circuits, or with the use of particular models of Smart TRVs.

For this I had a product such as the TP-Link Kasa system in mind.

Further information is available on our Heating Controls page.

Using Smart TRVs to fulfil measure might cost £100 or so and this is the path I should have chosen because this single measure on its own would have got me to a 69C rating cheaply.

If you are interested in TTZC, choose any works carefully with the assistance of an energy assessor beforehand.

I've always liked the concept of this product but I'd been avoiding it due to the normally high retail list price of around £650.

However, I had a long term search setup on eBay in case one came up, and in April 2026 I was lucky enough to purchase one for £255.

This is a heat exchanger which you retrofit underneath an existing bath. It uses heat from waste water exiting the bath to warm up incoming cold water to the mixer shower. This means slightly less hot water from the combi boiler is used when having a shower.

As a single measure this improves the EPC rating of this property by 0.5461 points which is close to what we need, but not quite.

We would therefore need to use this measure in conjunction with another.

For more informtion about WWHRS, please see our FGHRS and WWHRS page.

I've decided to proceed with these two options, partly because I've already bought the Easyfit+

• Waste Water Heat Recovery - Recoup Easyfit+
• Changing electricity tariff to single rate

This would increase the rating of this property to 69C.

Some time has passed since installation of the central heating system, some work has been DIY and I've not included the heating engineer's time installing the boiler controls. The gas connection charge is my best recollection too.

Gas connection to the property - £200 (2015)
Gas combi boiler install (full CH system) - £5,500 (2015)

Resolve secondary heating 'issue' - £0

Alpha Weather Compensation sensor (cannot claim) - £28

Alpha Climatic Controller (cannot claim) - £65

Change electric tariff to single rate - £0

WWHRS - Recoup Easyfit+ - £255

WWHRS x DIY install - £50

Total (estimate) = £6,098

Always discuss any improvement measures with an energy assessor before proceeding with works. This will ensure you know the outcome before you start.

I hope you've found this page interesting. If you would like to read more, take a look at our other Case Studies.