Heating Systems

At the time of writing the methodology for EPC assessments of existing dwellings is RDSAP 9.94. The much anticipated RDSAP 10 update is due in Q1 2025 and a significant methodology overhaul from RDSAP to the Home Energy Model (HEM) is proposed for 2026.

Here we consider heating systems that are used to heat the rooms in a property, and this is often called 'Space Heating' in the field of property assessment.

There is also the area of Water Heating which we cover on another page on this site, which relates to the system for producing Domestic Hot Water for use in mixer showers, sinks and basins etc within the property.

Sometimes the domestic hot water is heated by the same system that provides the space heating, and sometimes it is produced by a separate system.

Heating systems can make a very significant difference to the EPC rating for a property, but they can be costly to replace or update.

However, it is still possible to make small increases in your EPC rating by making smaller changes to the Heating Controlsfor example.

The largest gains may be experienced when moving from a system using an expensive fuel to one using a lower cost fuel. (eg from electric storage heaters to gas boiler or Air Source Heat Pump).

There are also a couple of situations related to the assessment methodology to mind out for which will cost you a few EPC points if you fall foul of them. We'll describe these in more detail in a few moments.

Let's work through Heating Systems and maybe you can spot something you can change to improve your EPC Rating.

In order to create a level playing field for EPC assessments so that one property can be easily compared to another, the RdSAP methodology makes some standardissed assumptions in regard to 'space heating'.

Consider the case where we have two identical properties, perhaps they are both 3-bed mid-teraced houses, both on the same estate, and both built at the same time and with identical heating systems.

In the first one we have a single person living in the property and they tend to only heat the rooms which they occupy such as one bedroom and the lounge, and have the heating on for as little time as possible in order to limit the cost of heating.

By way of contrast, in the second home we have a family of two adults and two children, with the chidren each occupying their own bedroom. They heat all the rooms all of the time because they can afford to and they like being warm.

Consider now that you are looking to purchase a property in this road and both of these properties were for sale.

You examine the EPC certificates for both properties in order to create a comparison which might help you consider one property over the other. 

Under the current methodology (time of writing : March 2025 - it is RDSAP 9.94), the current Energy Indicator Rating (EIR) on an EPC is entirely cost based - ie the rating is calculated entirely from the cost of running the property, taking into count the cost of lighting, cost of domestic hot water and cost of space heating, in relation to the floor area.

If the rating were to be calculated based on the individual useage pattern of the current occupier, it would be clear to see that the cost of running the first property would be much less than the cost of running the second property, resulting in perhaps a much more attractive looking rating for the first property.

For a prospective purchaser looking at the EPCs, these ratings would not be reliably representative of the building and therefore would not be of any use in making a judgment about the energy performance of those properties.

Therefore to avoid this happening, the RDSAP methodology uses a set of occupancy assumptions, and these same assumption rules are used across all domestic RDSAP EPCs so that ratings produced can be usefully compared with each other. 

For those that are interested, in terms of 'space heating' requirement, it is assumed the property is heated for 9 hours per day for 5 days per week (ie Monday to Friday), and 16 hours per day for 2 days per week (ie Saturday and Sunday). During these days, the living room is heated to 21 degrees C and the remainder of the dwelling is heated to 18 degrees. Overall, this heating pattern is in place for a period of 8 months per year (ie space heating is not required during four months over the summer).

It is important to bear this in mind as you read on about Heating Systems.

The EPC assessment allows for the recording of:

• The presence of up to two 'Main Heating' Systems
• The presence of one form of 'Secondary Heating'
• Any Heating Controls for the Main and Secondary heating systems.
• The count of 'Habitable' rooms in the property
• The count of 'Heated Habitable' rooms in the property
• How Domestic Hot Water (DHW) is heated - ie hot water to taps

We'll start with the number of 'Habitable' and 'Heated Habitable' rooms in the property.

'Habitable' rooms include any Living Room, Sitting Room, Dining Room, Bedrooms, Studies and similar, and also Kitchen/Diner (defined as being able to accomodate a table and four chairs) - Open plan rooms are counted as one room, including when only separated by an open archway, and if a door has been removed and the hinge holes filled in - for example the classic example of between a lounge and dining room.

Not included are: Any room used soley as a Kitchen (and is unable to accomadate a table and four chairs), Hallways, Stairs, Utility rooms, Landings, Bathrooms, Clakrooms, Ensuites and any room without access to natural light.

A conservatory separated by an internal quality door from a dwelling is also regarded as a habitable room, but a conservatory separated by external quality doors from the dwelling is not a habitable room as the conservatory is disregarded from the assessment. A conservatory separated by an open plan archway is regarded as part of the habitable room to which it is attached and is not counted as an addditional habitable room in it's own right.

We then count the number of those 'Habitable' rooms which are heated in one way or another. This could be by either a 'Main Heating' system, or by a fixed 'Secondary Heating' source. We'll describe these next. Note though that bedrooms with only open fire-places are disregarded from the heated habitable room count when identifying the heating systems (main and secondary).

So, we'll come back to these two numbers in a bit - the count of habitable and heated-habitable rooms. For us, where we are interested in maximising our EPC rating, we're interested in whether there's a difference between the two numbers, ie whether all the 'Habitable' rooms are heated or not. Ideally we want all the Habitable rooms to be heated.

Next, we work out what 'Main Heating' systems and 'Secondary Heating' sources are present in the property.

A main heating system is often:

• Gas Boiler (with radiators or under-floor heating)
• Oil Boiler (with radiators or under-floor heating)
• Electric Storage Heaters (when they are the main source of heat)
• Electric Panel Heaters (when they are the main source of heat)

Secondray Heating can include:

• Fixed Electric Panel heaters
• Electric towel rail radiator in the bathroom or ensuite
• Electric plinth heater in the kitchen
• Electric feature fireplace
• Electric ceiling heaters
• Electric under-floor heating mats

• Open Fireplace (with grate present)

• Closed Log Burner
• etc.

The majority of properties have one main central heating system, and possibly a source of Secondary Heating.

Several details are recorded for up to two Main Heating systems, and just a single heating code can be entered to describe one form of Secondary Heating, if present.

Devices need to be fixed in place in order to be recorded. Portable electric fan heaters would not be recorded as a form of Secondary Heating because they are not fixed in place. A fixed electric feature fireplace in a lounge however would be recorded.

We mentioned earlier that the EPC rating (for existing dwellings) is entirely related to the cost of running the property, taking into consideration the cost of lighting, domestic hot water and 'space heating'.

This contrasts with the methodology for non-domestic EPCs (i.e. commercial buildings), whose ratings are entirely based on CO2 emissions instead.

Because of the involvement of cost in the calcualtion of the EPC rating for dwellings, the type of fuel used by the heating system significantly affects the EPC rating.

The fuel costs used in the calculation of the EPC rating for an existing domestic property are available to view in the SAP 2012 document on the Building Research Establishment (BRE website):

https://bregroup.com/expertise/energy/sap/standard-assessment-procedure-2012

On that page, scroll down to the SAP methodology and approved software' section and click on the document: 'SAP 2012 Document'.

The fuel prices used are located in Table 12. These were apparently last defined in 2014, and these values have been in use for the last 10 years since then.

Note that these values are different to the fuel costs used in the formulation of the EPC Recommendations, which are updated periodically and are in the separate document: 'SAP2012 Prices used by SAP and RdSAP for calculation of fuel costs.'

The complete list is quite large, and I have only reproduced the most common fuel types and the unit price information here. Some fuels have additional standaing charges as well, for example.

Of the common fuel types listed above, mains gas is the cheapest and is therefore likely to be the best choice currently for a good EPC rating.

The most expensive in this list is peak rate electricity on a standard tariff (and also on the 7 hour tariff). This as a fuel type would likely lead to a very poor EPC rating (Heat pumps are an exception however).

Peak rate electric would be the type of fuel used by fixed electric panel heaters, fixed convector heaters etc.

Storage heaters would produce a better rating because they use cheaper rate electricity during the night to charge up, and release the eat during the day.

Oil boilers in comparison are better, and Gas boilers would be better again. This is in terms of being lower cost, and producing a better EPC rating. They are of course not so good in terms of CO2 emissions.

(Note that EPCs will change in the near future and it looks like the single Energy Cost related metric will be replaced by multiple metrics. Strategies for improving EPC ratings will therefore change at that point - see our The Future of Domestic EPCs page for more infomation). 

A quick note about efficiency here, as some people get confused. Electric heaters such as panel heaters, fan heaters etc. can only be a maximum of 100% efficient. That means that if we have an electric heater and it uses 1kW of electrical energy, it can produce a maximum of 1kW of heat output. In comparison, although gas condensing boilers are often in the low 90s% efficient, the much cheaper price per kW of heat within the gas makes them much cheaper to run overall, and that is what's important under the current regime for a decent EPC rating.

We must however talk about Heat Pumps, which are a bit of an exception. They also run on electricity but they work by moving heat from one souce to another instead of actually generating that heat. Their efficiency (referred to as Coefficient of Performance - COP) is highly dependant on the design and installation of a system but would normally be between 300% to 450%. Because of this high level of performance, they are an efficient form of heating that runs on electricity, and combined with the aspect of CO2 reduction are seen as the future of domestic heating in the UK.

Heat pump efficiency can vary so much depending on system design and installation, so the specific efficiency value used in an EPC assessment is taken from a data entry in the PCDB for the specific heat pump installed.

Currently, the domestic EPC methdology does not favour heat pumps over gas boilers because it generally calculates that heat pumps cost more to operate than gas boilers.

Generally, and bearing in mind the exception of Heat Pumps that are a very efficient heating system using electric power, if you change your heating system from using a more expensive fuel, to a cheaper fuel, you would expect your EPC rating to improve.

Always check with a local Domestic Energy Assessor however before making any changes as this will make sure you know what the effect will be, and you'll be making an informed decision.

Let's take a look at our Case Study 3, which is a property that has no Main Heating system at all, and no form of Secondary heating present either. This example demonstrates possibly the most extreme case of improving an EPC rating by upgrading a heating system.

The EPC rating is currently very poor indeed - it's a 30F despite all other aspects of the property being quite good. The rating is this low because when heating is absent, the RDSAP methodology must assume the worst case heat source will be used to fulfill the shortfall - the use of peak rate electric heaters.

In the Recomendations on the EPC for this property, it indicates that installing a central heating system based around a condensing gas boiler would bring the EPC rating up to 74C (combined also with solid floor insulation) - perhaps we could interpolate that it would be 71C without the solid floor insulation. 

So just changing the heating system results in a massive improvement of 41 SAP points.

This is probably the most extreme example and it's this big because of the very large difference in the cost of 'space heating' (and also domestic hot water in this case) by using peak rate electricity as a fuel type, compared to that of mains gas in an efficient condensing combi boiler.

A whole central heating system including pipes and radiators, where there wasn't one before, will cost a significant amunt of money perhaps up to £10,000, so it would take a significiant investment to implement.

Also, if gas is not already present at a property, there may be additional costs in getting a gas supply connected, and in some cases that could be very expensive or just not feasibly possible at all, depending on location and building type.

In the above case study there used to be a gas boiler present at the property, and a gas meter was present at the time of the EPC assessmnet being conducted. Therefore the EPC Recommendations included an option for a gas boiler.

If a gas meter had not been present, then that recommendation would not have been included on the EPC.

If you don't have gas, and you were interested in getting it connected, find out from your energy supplier how much it would cost. It might cost less than you think. I had to get gas connected to our property, and it only cost £200-£300 back in 2015 because there was a gas main running directly in front of our house.

Rather than using gas however, the future direction is really that of Heat Pumps. this is partly due to their efficiency on electric power, but also due to the move away from carbon based fuels, in order to meet the Government's committment to reduce carbon emisions by 2050.

It has previously been discussed that in the future there might be a ban on gas boilers in new builds, and from some date further in the future for gas boilers to be banned from being installed or replaced in existing dwellings. Oil boilers could be similarly affected. Time will tell.

We've already talked about Main Heating systems, although we have kept the conversation fairly light in terms of complexity.

In addition, the EPC assessment also allows the recording of one form of 'Secondary heating' as well.

We listed some examples above, but in summary these could be in the form of an open fireplace (with a grate), or a fixed electric feature fireplace, or an electric heated towel rail radiator in the bathroom for example, and these tend to be local heaters.

When a form of Secondary Heating is identified and recorded on an EPC assessment, the RDSAP methodology assumes that a proportion of the floor area of the property is heated by it.

This varies from 10% to 20% of the floor area, depending upon the type of fuel used. Peak rate electric is the worst at 20%, and wood burners for example are at 10%. These values are listed in a Table 11 of SAP 2012, in the document we linked to above.

Note that the presence of a form of Secondary Heating is recorded, irrespective of whether that heating device is actually operated by the occupier of the property. i.e. if an assessor notices a form of Secondary Heating is present they must record it in the assessment.

To be recorded in the EPC assessment, the form of Secondary heating has to be fixed in place. For example a portable electric heater would not be counted, but a panel heater fixed to the wall would be.

There are a number of criteria to determine whether an electric feature fireplace is 'fixed' or not, and an open fireplace would need a grate present to be counted.

Although forms of Secondary Heating can really look the part in a property and add to it's feel, there are two scenarios where Secondary Heating can work against your EPC rating.

These are:

• Where Secondary Heating uses a fuel that is more expensive that that used by your Main Heating System (or uses the same fuel but less efficiently)
• Where you have any un-heated habitable rooms, the use of Secondary Heating is assumed by the methodology, and if none has been identified in the property already then portable peak rate electric heaters will be assumed.

(Note however that these things don't seem to apply if your main heating is provided by storage heaters)

You won't see any EPC recommendations telling you about either of these two things - ie to remove a Secondary Heating device to increase your EPC rating, or to make sure all your habitable rooms are heated by your main central heating system in order to increase your EPC rating.

We'll discuss both of these situations next.

Secondary Heating that uses a more expensive fuel than the Main Heating System

If you have a good central heating system, and that is the source of heating in all of your habitable rooms, but you also have a source of secondary heating recorded that uses a more expensive fuel (such as peak rate electric) then this will adversely affect the EPC rating.

See my example below where this would reduce the rating on my property by 6 SAP points. This is regardless of whether you actually use that item of secondary heating or not. The EPC assessment does not consider how you actually use the heating systems.

(Note that this does not seem to apply if your main heating is provided by storage heaters).

Unheated Habitable Rooms result in the assumed use of Electric Secondary heating in the absence of any declared Secondary Heating

If you have a difference between the number of habitable rooms, and the number of heated habitable rooms in your property, and you have no other form of Secondary Heating declared, then the RDSAP methodology will assume that portable electric heaters will be used to fulfill the heating shortfall.

Again, if your main heating system operates on a cheaper fuel, this will reduce your EPC rating, and in the example of my house it reduces it by 6 SAP points.

(Note that this does not seem to apply if your main heating is provided by storage heaters).

If you have electric storage heaters and you are wanting to improve your EPC rating, as you research your options online you might come across adverts for electric panel heaters. Some of these can be very emotionally enticing, with a description such as:

"Electric Radiators offer a modern, energy efficient heating solution for any space. Unlike traditional radiators, electric radiators provide 100% conversion of energy to heat, precise temperature control for each room and the latest energy saving technology, ensuring optimal comfort and reducing energy wastage."

These adverts often mis-represent the concept of 'efficiency' with the actual subject of reducing energy consumption by reducing the temperature you heat your living space to. 

At the end of the day, these are just electric panel heaters and like any other electric panel heater will use peak rate electricity during the day to heat your home. If you fit them as a replacement for your storage heaters your EPC rating will go down because you are now using peak rate electricity to heat your home rather than overnight cheaper rate electricity which storage heaters use to charge up.

Whatever meaning you try and create into the situation, the cost of heating will be higher and because the EPC rating for existing dwellings is an entirely cost based metric, the rating will be worse as a result.

Remember the standardised assumptions we mentioned earlier on this page? Well, however 'efficient' you think the electric panel heaters are, the RDSAP methodolgy assumes that rooms in the property are heated up to 21 or 18 degrees C (Living room/rest of dwelling), for 9 or 16 hours per day (Weekdays/Weekend), and the heating system is in use 8 months of the year.

There are many examples in online forums where property owners express their complete surprise and disappointment that their EPC rating has gone down significantly in this situation.

These people have been duped into making this change and didn't understand the consequences of their actions.

Therefore, avoid fitting fixed peak rate electric panel heaters unless you are doing so as part of a carefully calculated installation - you might be tempted to do this in combination with at least one High Heat Retention Storage Heater in a small property with a limitation on the budget for example - see our High Heat Retention Storage Heaters page.

Always contact a local domestic energy assessor for guidance on the best way forward when wishing to improve your EPC rating.

In the example of my own 1950s terraced property, which we cover in Case Study 2, I recently re-assessed it to see what the EPC rating would be, and it calculated as a 68D.

I have a condensing gas combi boiler fitted in 2015, and no secondary heating recorded because I have made the decorative electric log burner in my fireplace detachable.

I have 5 Habitable Rooms and 5 Heated Habitable Rooms. If however I redcue the number of Heated Habitable Rooms by a count of 1 - effectively recording that I have one Habitable room in my house that is not heated by the main heating system, the following happens:

In the absence of any recorded form of Secondary Heating in the property, the RdSAP system will decide that additional heating will be required to heat that room and it will assume, and declare on the EPC, that portable electric heaters will be used.

The EPC rating on my property, due to that one change, reduces by 6 SAP points down to 62D, which is a really significant drop.

Similarly, from the baseline of 68D, if I had not changed the wiring for my decorative electric log burner, and it was therefore still considered a fixed device and had to be recorded as Secondary Heating, then the EPC rating would also have reduces by 6 SAP points to 62D.

One approach to avoiding this situaton therefore is to ensure all your rooms that are classified as 'Habitable' rooms are heated by the Main Heating system in the house, and remove any forms of secondary heating (particularly electric) if your main heating system runs on a cheaper fuel.

You won't see either of these things listed in the recomendations on an EPC.

Note that other combinatons of heating fuel type may not be of such a concern. In an example of a large detatched property I assessed which had an oil based boiler as it's Main Heating, and a log burner in the lounge as Secondary Heating, the presence of that log burner did not detract from the EPC rating due to the similar costs of those two fuel types, so it depends on the individual property and combination of heating/fuel type.

As mentioned elsewhere, check with a local energy assessor to see what difference would be made with your particular property before proceeding with any works.

Many properties have a boiler as their main heating system and if this is the case, then this can be recorded either by looking up the exact make and model of boiler in a database from the EPC assessment software, or using a generic heating code to describe the type of boiler instead.

The best method is to locate the boiler in the database, known as the PCDF (or PCDB) as this will import the most accurate information about the boiler.

If the boiler cannot be identified, or cannot be found in the PCDB then the generic heating code wil result in less accurate figures for efficiency and performance of the boiler when calculating the EPC rating.

If your boiler is slightly out of the ordinary or does not have a GC number identified on it, perhaps prepare as much documenation for it before your energy assessor arrives so that they can make best efforts to locate the boiler in the database.

Check to see if you can upgrade your Heating Controls to try and improve your EPC rating.

Check to see if you are able to help identify the Heating Pump Age for your energy assessor.

Here we take my property (covered in Case Study 2) and model it with different forms of heating system. In each case we note the EPC rating as follows:

In the above table, all references simply for 'gas' means 'mains gas' rather than LPG.

You may already have a heating system in your property that runs on a cheap fuel, but you might be able to improve it further by looking at the 'Heating Controls' that you have connected to it.

Look next at our Heating Controls page to see what might be possible. 

Click here to return to our 'Improve Your EPC' main page, and see if there is another way you could improve your EPC rating.