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 Hone Energy Model (HEM) is proposed for next year.

This is a 1950s terraced house previously owned by the local housing association and auctioned off for sale at the end of its last tenancy. It’s latest EPC was recently conducted and the rating is a quite reasonable 69C - but it's only just in the coveted C band.

I think it can be raised to a mid-C band rating fairly easily though by making some simple and cheap tweaks to the building. This might look better to any prospective purchaser of the property in the near future and also create some margin to stay within the C band when the above mentioned changes in EPC methodology happen moving forwards.

I live in an identical house and I know that my house could achieve a 69C or 70C with a little effort, and that’s without cavity wall insulation (CWI), so for this property with a 69C including CWI, leads me to believe there is potential for some improvement.

I’ve spotted one thing I think has reduced the current EPC rating and once that's fixed, I’ve also got two other things I think can improve it a little bit further too at minimum cost, which is my criteria for this property.

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, a programmer and thermostat. The radiators do need replacing as they are too small, but this doesn’t affect the EPC rating.

This boiler and the heating controls provided with it are clearly sufficient to heat the house effectively, and efficiently, but for some reason there is an entry in the Features list for a form of additional 'Secondary Heating' of: 'Electric Room Heaters'.

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 considerably, and at this stage I would hazard a guess that this may be by as much as 6 SAP points (ed: it actually turned out to be 4 points). We’ll confirm this later by modelling once we get the keys to the property and can conduct our own real 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 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 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).

Other fuel types will have a lower comparative cost difference and lower assumed floor area use - so if you had instead say an oil based non-condensing boiler as a main heating system, and the secondary heating was a closed log burner then there might not even be any difference to the EPC rating. This would be due to the smaller relative difference (if any) in fuel cost and smaller assumed heated floor area.

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.

For this house then, all I need to do, asuming the EPC assessment is accurate, is locate any fixed electric heater that is present, remove it, and to be safe I will double check that all habitable rooms are heated by the gas boiler somehow (radiators in this case) and I would expect the EPC to rise – my estimate from a property exactly like this one is perhaps 6 SAP points (ed: actually 4 points in the end).

Moving on further, there are two things we can look at regarding the main heating system, each of which are likely to 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 load compensating thermostat and programmer. This is referred to as a type of 'Advanced Heating Control' within an EPC assessment. 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 that I will 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 '2013 onwards' rather than 'Unknown'. This boiler is a combi-boiler and the pump is located within the boiler casing so is not ordinarily visible.

Looking at the boiler, it's a Worcester Greenstar 30i ErP condensing gas combi-boiler. The label on the boiler indicates the Gas Council number is: 47-406-062. This number categorically identifices the make and model of boiler. It's currently fitted with a 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 setting on the boiler.

We are going to replace this thermostat/programmer with an ‘advanced heating control’, that modulates (adjusts) the flow temperature of the water from the boiler through the radiators based on either or both of these types of 'compensation':

• Load Compensation – using 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 does 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 you have the boiler on for longer.

So long as we choose an advanced heating control that is recognised within the EPC assessment system as compatible with our boiler then our EPC rating should increase slightly.

Our parciaular boiler does not support 'OpenTherm' and instead uses the proprietary Worcester Greesnstar EMS control bus so we will choose a Worcester Advanced control to match.

If the boiler had supported OpenTherm I would have looked into getting a Nest Learning Thermostat, but with this boiler it would have only operated in an ON/OFF mode.

The first step is to go to the Product Characteristics Data Base held by the Building Research Establishment (BRE) 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' , 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 listed in the list of supportbed 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 in reality it is). 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.

For this house I eventually chose the Worcester Comfort I RF thermostat and programmer which provides load compensation. 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 thermostat also has a very simple appearance which should keep non-technical owners comfortable.

I’ve already purchased a second hand one on eBay for £44 and we’ll have that fitted when we have the boiler moved during the renovation. We’ll be able to model it's presence in advance using the EPC software however to see what difference it will make once we get full access to the property.

Next we consider the age of the heating pump.

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.

The application of 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 likely the EPC rating will be uplifted by 1 point.

What I need to do is firstly 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.

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 identify this example 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

These together should easily support the ascertion that the heating pump is 2013 or later. We just need to take sufficient photos that include geo-location meta data at the property - any modern smartphone should be sufficient. I'll take photos both close up and from mid-distance showing location context of the boiler in the property with the case still off.

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

We've now got permanent access to the building.

I've run an EPC assessment and found the following:

There's no longer any Secondary Heating in the property at all. From photographs taken across first and second viewings we can tell there was an electric feature fireplace in the living room, but that has since been removed.

All the habitable rooms are heated by the main gas fired central heating system.

That's great news and the EPC rating has increased by 4 SAP points due to this.

I've been able to fit the Worcester Comfort I RF controller to the boiler, and I've also been able to take a photo of the heating pump within the boiler and confirm it was manufactured in 2018 and has an EEI < 0.23.

These two things individually would have added 1 SAP point to the EPC rating, but with them both together I also only get 1 SAP point increase overall. I was a bit disapointed as I could perhaps have not purchased that heating controller after all.

The result has come out as a 74C, which is 5 points up on the previous EPC rating and I'm pleased with the improvement.

This result sits more firmly within the C band, and therefore has some margin to withstand any skew when the EPC methodology changes in the future.

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

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

For this property, clearly the path to go down would be installing Solar Photovoltaic panels if we wanted to significantly improve the EPC rating further. This provides the greatest improvement at a resonable cost.

Always engage with a local energy assessor to see what improvements could be gain for your property before proceeding with any works or spending money.