Desk with Laptop, Calculator, Files and small model of house with epc colours
Desk with Laptop, Calculator, Files and small model of house with epc colours
EPC Works
EPC Works

Case Study 1 - 1950s Terraced House - Improving a C Rating at Minimum Cost

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.

Description

This is a 1950s terraced house and it has a current EPC which was conducted very recently. It has a very reasonable rating of 69C.

 

This is only just in the C band, on the lower threshold, but I think it could be raised to more of a mid-C band rating fairly easily by making some simple and cheap changes.

 

A slightly higher rating could look better to any prospective purchaser of the property in the future and also create some margin to stay within the C band if the future changes in EPC methodology create any skew in ratings.

 

I live in an identical house to this one, and I know that my house could achieve a 69C or 70C with a little effort, and that’s without cavity wall insulation (CWI). This property here already has CWI, so I think that the 69C rating has some potential for improvement.

 

I’ve spotted one thing I think has reduced the current EPC rating and once that's fixed, there are two other things I also have in mind which could improve it a little bit further at minimum cost.

Checking the EPC Features List

Firstly let’s take a look at the Features List on the existing EPC certificate…

We can see the insulated cavity wall being declared at the top, and the other items all appear 'Good'. What I'm interested in the most however, is the last line that reads: "Secondary Heating: Room heaters, electric".

 

I’ve viewed the property twice, internally, and I've seen it has a modern gas condensing boiler fitted in 2018 with radiators, TRVs (on at least 50% of the radiators), a programmer and a thermostat.

 

This boiler and the heating controls provided with it are clearly sufficient to heat the house effectively, and efficiently. In addition however, there is an entry in the Features list for a form of additional 'Secondary Heating' of: 'Electric Room Heaters'. See our Heating Systems page for further reading.

 

The important thing to be aware of is that in this situation the RDSAP methodology will assume that 20% of the floor area of the property is heated by this peak rate electric heating source, even if it is not actually used by the occupants of the property.

 

As peak rate electric room heaters are far more expensive to run than the gas boiler, the EPC rating will have been reduced by a number of points. We’ll confirm this later by modelling once we get the keys to the property and can conduct our own EPC assessment.

 

With a form of Secondary Heating listed, the effect on the EPC rating is dependant on two things in particular. One is the relative cost of the fuel of the secondary heating compared to the fuel used by the main heating system. The second is the proportion of the floor area that RDSAP assumes is heated by the secondary heating. That area is between 10 and 20 percent and is dependant on the fuel type.

 

Peak rate electric heating is the worst cost of the mainstream fuel types, and at 20% it carries the highest floor area percentage too. (For reference, these relative fuel prices and area percentages are detailed in Tables 11 and 12 of SAP 2012 appendix S  documentation available on the BRE website).

 

Looking back at the Features List on our EPC, looking closer, notice that on the end of the description for "Secondary Heating: Room Heaters, Electric" we do not have the word "assumed" in brackets. This means the energy assessor has reported that a fixed form of electric room heater is actually present somewhere in the property.

 

Had we had the word "assumed" in brackets, then the presence of this heating would have been inserted by the RDSAP methodology automatically perhaps due for example by there being a habitable room in the property that is not heated by the gas boiler.

The Chosen Improvements

For this house all we need to do, asuming the EPC assessment is accurate, is locate any fixed electric heater that is present, remove it, and double check that all habitable rooms are heated by the gas boiler somehow (radiators in this case) and we would expect the EPC rating to rise.

 

In addition, there are two things we can look at regarding the main heating system, each of which might make a 1 SAP point improvement to the EPC rating for this particular house.

 

One is by swapping the existing ON/OFF  thermostat/programmer out for a 'Compensating' thermostat & programmer. We will do this when we have the boiler moved as part of the renovation of the property because access to the inside of the boiler is required and I'm not GasSafe qualified.

 

The other approach is to take photographs of the heating pump within the boiler before our heating engineer puts the casing back on. I expect to be able to declare the pump age in the EPC assessment as being of age: '2013 onwards', rather than 'Unknown'.

 

This boiler is a gas combi-boiler and the pump is located within the boiler casing so it's not normally visible.

 

Compensating Heating Control

The boiler is a Worcester Greenstar 30i ErP condensing gas combi-boiler. The label on the boiler indicates the Gas Council (GC) number is: 47-406-062. This number categorically identifices the make and model of boiler. It's currently fitted with a standard Worcester DT20 RF programmer and thermostat.

 

This thermostat/programmer combination provides basic ON/OFF control of the boiler as the room temperature falls below and then rises above the target temperature on the thermostat. When the boiler fires up, it heats the water sent through the radiators to a fixed temperature, determined by a dial on the boiler.

 

We're going to replace this thermostat/programmer with one that provides a form of 'Compensation' control. This will modulate (i.e. vary) the flow temperature of the water from the boiler through the radiators based on either or both of these types of 'compensation':

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

If we can find a product that provides both of these easily then great, we'll choose that, otherwise a product that just provides load compensation on its own would be fine.

 

Both of the above compensation approaches generally reduce the flow temperature of the water through the radiators thus ensuring the gas boiler operates in condensing mode as much as possible and that increases the efficiency of the boiler. You'll notice the radiators feel cooler to the touch and the boiler runs for longer periods of time.

 

So long as we choose a Compensation control that is recognised within the EPC assessment system as compatible with our boiler, then our EPC rating could increase slightly.

 

Our particular boiler does not support 'OpenTherm' and instead uses the proprietary Worcester Greenstar EMS control bus so we will have to choose a Worcester device.

 

If the boiler had supported OpenTherm I would have been interested in a Nest Learning Thermostat, but with this boiler it would have only operated in an ON/OFF mode, and also, I have not been able to locate the Nest in the database from within the EPC software.

 

The compensating controller that we choose must be listed in the Product Characteristics Database (PCDB) held by the Building Research Establishment (BRE). If it is not listed in this database, or if it is there but it is not available in that database from within the EPC software, we won't be able to record its presence, and we won't get any increase in our EPC rating.

 

The first step then is to take a look in the Product Characteristics Database on the BRE website. It's located at:

 

https://www.ncm-pcdb.org.uk/sap/searchpod.jsp?id=17

 

For our Worcester 30i ErP boiler, we click on the big button for 'Compensating Boiler Controls' . On the next page we select the Fuel as 'mains gas' and the Brand Name as 'Worcester'. Leave the other two options as they are (i.e. don't select anything), and click the 'Search' button. We then get the following results:

For your own boiler, you need to research the advanced controls listed by your manufacturer, to work out which ones interest you the most.

 

Importantly, you must go into each listing (click the corresponding Details link in the right hand column) and make sure your boiler is present in the list of supported boilers for that particular device. (I've had an issue with an Alpha climatic controller not being listed as compatible with my Alpha boiler even though it is - see our page on resolving PCDB issues for more information).

 

Also cross-reference this information with your own research online for each device to make sure it is actually compatible with you boiler. You can't rely on the accuracy of the information within the PCDB.

 

Finally it would be worth checking with a local Energy Assessor to make sure the control is available from within the EPC assessment software, and whether it would make a difference to your rating.

 

For this house I chose the Worcester Comfort I RF thermostat and programmer which provides load compensation only. It has a listing in the PCDB and our boiler is present within the list of boilers that are compatible with it (in the PCDB). The device is also available to select from within the EPC assessment software.

 

The thermostat also has a very simple appearance which should keep non-technical future owners comfortable.

 

I’ve purchased a second hand one on eBay for £44 and we’ll have that fitted when we have the boiler moved during the renovation.

Worcester Comfort I RF Heating Control Worcester Comfort I RF Heating Control

Next we consider the age of the heating pump.

 

Heating Pump Age

During an EPC assessment, the Domestic Energy Assessor can select from the following options to describe the age of a central heating pump: ‘Unknown’, ‘Prior to 2013’, and ‘2013 or later’.

 

This option relates to the introduction of the EU’s Energy-Related Products (ErP) Directive which obliged manufacturers and importers to provide consumers with products that were more energy and resource efficient.

 

This directive included heating pumps for central heating systems. These pumps move the water through a boiler and around the radiators or underfloor heating pipes in your house, and they can be operating for considerable periods of time.

 

Although there were stages in the applied legislation, the effect is that if an energy assessor can identify a heating pump in a central heating system to have been manufactured to the required modern efficiency requirement, and they indicate this within the EPC assessment by declaring the age of the heating pump is '2013 or later', for a house like our 1950 teraced property, it is possible the EPC rating might be uplifted by 1 point.

 

What I need to do is make sure the pump is genuinely dated from 2013 onwards, and then I need to record sufficient evidence to support that claim in case my EPC is ever audited by the accrediation scheme that I subscribe to.

 

Example Heating Pump from a Worcester 30i ErP Boiler Example Heating Pump from a Worcester 30i ErP Boiler

The photo above is from an eBay listing for a heating pump from a Worcester 30i ErP combi boiler, and this is what I will be looking for inside my boiler.

 

The two things that can identify a pump as qualifying for being given an age of '2013 or later' are:

  • The specification that is printed on the label indicating that the pump EEI is less than or equal to 0.23
  • The date of manufacture that is embeded in the Production Code: PC1550 - This represents 2015, week 50

For this pump which is contained within the case of a combi boiler it is the EEI value in particular which is the required evidence. See our Heating Pump Age page for more information.

 

For evidence requirements of the EPC assessment, we just need to take sufficient photos of the pump that include geo-location meta data at the property - any modern smartphone should be sufficient. I'll take photos both close up (showing the pump label) and from mid-distance (showing location context of the boiler) with the case still off.

 

That's it for now. I'll add an update once we get access to the property.

Update October 2024

We have gained permanent access to the building, and I've run an EPC assessment.

 

After looking round the property I've confirmed there's no longer any sources of 'Secondary Heating' present at all.

 

I've looked back at photographs from the original property listing on Rightmove and I can see there was a fixed electric feature fireplace in the living room, but this was removed prior to completion of the sale of the property:

Fixed Electric Feature Fireplace Fixed Electric Feature Fireplace

I've also confirmed that all habitable rooms in the property are heated by the main gas fired central heating system.

 

So that's great news, and the EPC rating has increased by 4 SAP points due to this alone, to a 73C, without making any changes to the property myself.

 

Next, we've had the boiler moved, and I've fitted the Worcester Comfort I RF controller, and taken a photo of the heating pump within the boiler.

 

The label on the pump confirms it was manufactured in 2018 and has an EEI < 0.23. This means it can be declared as having an age of '2013 or later'.

 

Here it is:

The Heating Pump in my Worcester 30i ErP boiler The Heating Pump in my Worcester 30i ErP boiler

The new controller and heating pump age declaration individually would each add 1 SAP point to the EPC rating, but with them both together I also only get 1 SAP point increase overall.

 

This is likely due to fractional rounding, and therefore I didn't need to purchase that heating controller after all, but that's fine, the financial outlay has been small. See the section below for more about the floating point SAP rating before it was rounded to an integer.

 

So, the result has come out as a 74C, which is 5 points up on the previous EPC and I'm pleased with the improvement as the rating sits more firmly within the C band.

Further Potential Improvements

Having full access to the property now, we can model EPC rating improvements from other measures too:

Description EPC Rating Change
Increase Loft Insulation from 200mm to 300mm 0
Solid Floor Insulation (100mm) +1
Solid Floor Insulation (150mm) +1
Change Double to Triple Glazing 0
Solar Thermal Water Heating (Unknown Details) +1
Time & Temperature Zone Control +1
Flue Gas Heat Recovery (Worcester Xtra 2015) 0
Waste Water Heat Recovery - Recoup EasyFit+ (*) 0
Heat Pump (aroTHERM plus 7kW & AI 150l PP) 0
Wind Turbine (2m dia, 2m above ridge) +1
Wind Turbine (4m dia, 4m above ridge) +5
Solar PV Panels (2.5kWp, West, 45 deg) +10
Solar PV Panels (5.0 KWp, West/East, 45 deg) +21

* = strictly not quite applicable for this property due to the bathroom being a wet room

 

The rating improvements indicated above are from the new 74C baseline for this property. The rating change displayed is for just that one single improvement listed, and is not in combination with any other change.

 

The EPC rating and any improvements are indicated using an integer value, or in other words a 'round number'.

 

Behind the scenes though the rating and any recommendations are actually calculated to a fractional number and then rounded to an integer.

 

It's possible therefore that combining a couple of measures in this list with zero improvement might result in a single point improvement. It would be best to model that before proceeding with any work however.

 

The fractional rounding of the EPC rating can be seen in the SAP Worksheets document which is a data file produced in the background by the assessment software when an EPC is calculated, and lodged to the national register.

 

Here is the part of that document where it rounds the final 74C rating for this property:

The rating was calculated as 73.7060 and rounded up to 74.

 

For any measures to improve this rating by a single point to 75C, the rating would need to improve to at least 74.50 which would then be rounded to 75.

 

This would need a raise of 74.50-73.7060=0.794 SAP points. 

 

Looking back at the table, if I were looking for further improvements, for a small increase of +1 SAP point I would probably look to install Time & Temperature Zone controls. For that, a couple of Smart TRVs would probably fit the bill, and the cost would be relatively low, likely below 200 GBP.

 

For significant improvement, the path would be to install Solar Photovoltaic panels.

 

The other options for floor insulation and solar thermal water heating just wouldn't result in much of an improvement, particularly considering the cost and upheaval of the work.

Finally...

The information here is relevant to this particular property. Always check with a local energy assessor to see what improvements could be gained for your property before proceeding with any works or spending money.


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