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House buyer's & renter's guide to reading an Energy Performance Certificate (part 1)

Posted by Linn Rafferty on 26 August 2011 at 9:30 am

This is a detailed house-buyers / renters guide to reading an energy performance certificate (EPC). It covers what you should look for and what it all means. This first part, of two, looks at some first impressions, and how to read page one.

Why is it important to me?

People are sometimes surprised how much difference a good EPC rating can make to your household bills.  Although not every bill is reflected in the EPC rating (which only looks at the home’s energy costs), for many people the majority of their monthly bills are for providing heating, hot water and electricity for lighting – exactly the costs which the EPC rates on an A to G scale.

In a brand new home (where the EPC rating could be as high as B) the heating costs will be low and other bills will usually dominate, but this isn’t normally the case for an older home.  In a home with an EPC rating of perhaps F or G, the heating bills will be the biggest drain on your monthly budget, unless you choose to accept lower levels of comfort (cooler temperatures, shorter heating times); and who doesn’t want to be comfortable in their new home? 

The EPC will tell you whether you will be able to live comfortably, or have to settle for wearing woolly jumpers indoors to bring your fuel bills down.

If you don’t ask, you often don’t get!

Whether you are thinking of buying or renting, you should be offered the EPC whenever you are given information about a property you are considering.  Information clearly includes the property brochure, but it could also mean the online information you see on a property portal like Rightmove, or an agent’s own website.  If you are not offered the EPC at this point, make sure you ask for it.  

A common reason why agents don’t comply with the law is that buyers / renters don’t ask to see it, and so it’s left until the solicitor insists on seeing it as part of the legal stuff.  By this time, it’s rather too late for the buyer to make any decisions based on the information it contains! 

For renters, as a solicitor isn’t normally involved in the transaction, the EPC is often never provided.  Since the private rental sector is becoming the main housing source for today’s under-40s (nearly 4 million homes), this represents a lot of people not being given the information they are entitled to.

What does page one of the EPC tell us?

The two most important things on page one are the rating graphic and the table of fuel costs.  Taking them in turn:

The rating graphic – This is the headline message provided on page 1 of the certificate.  Currently there are two colour coded graphics, one in red/green and one blue/grey.  The second, blue/grey, graphic will be dropped next year so I’ll not consider it further here.  

The red/green graphic rates the home’s energy efficiency – that is, how much of what you pay for (heat, light, etc) do you get per pound spent on energy bills. This calculation is done per square metre of floor area, so that different sized homes are rated on an equal footing. Otherwise, a smaller but less efficient home might rate more highly than a larger, more efficient one, purely because it has less space to heat.

The graphic has two arrows – one indicating the home’s performance now, and the second showing the home’s potential rating if the most cost-effective recommended measures are all installed.  This potential rating is very important – it tells you if the home is capable of being improved at a reasonable cost, and how much better it could be after improvement.  

"Can I get another EPC done if I think mine is incorrect?" Find out in our blog.

The arrows are both numbered with the SAP rating, before and after improvement; SAP is just the technical name for the method used to assess the home’s energy performance. 

It’s the difference between these two numbers, rather than the difference in the rating bands, which tells you just how much the home can be improved.  If the rating is low (say, E, F or G) and the potential is also low (say, an improvement of no more than 10 SAP points) and you want to be warm at reasonable cost, then this home is probably not for you.

The estimated energy use, CO2 emissions and fuel costs

Page one also provides a table (see above) that isn’t explained at all well.  This table will be replaced next year, but for now, it’s best to ignore the first two rows (energy use, CO2 emissions) and concentrate on the last three rows, indicating the home’s energy costs; these estimates reflect the floor area of the home, so for two homes with the same EPC rating, this table will show higher costs for the larger home.

The table gives estimates for heating, lighting and hot water, and the second column shows how much these costs could be reduced if the recommended improvements were made. Just like the rating graphic, it’s only the cost effective recommendations that are taken into account here, so the most expensive recommendations are ignored. If you have a large budget and decide to include the most expensive recommendations, the savings should be larger than estimated in this table.

If you have limited funds for home improvements, it makes sense to work on the item that has the biggest cost saving potential.  This is often, but not always, the heating, but in well insulated homes, lighting or hot water can be worth tackling first.

It’s worth knowing that these costs are averages for different households, based on an assumption that the home is heated for 9 hours each weekday and 16 hours a day at the weekend, with the main living area heated to 21°C and the remainder of the home to 18°C. 

Why isn't draught-proofing EPC's number one recommendation? We answer this question in our blog.

Your heating preferences may be different, in which case the actual heating savings will also differ, and could be either higher or lower – if you use more, you will save more. The hot water and lighting estimates are based on the size of the home: for example, it’s assumed that a four bedroom home will be occupied by at least 4 people, and a one bed flat will have 1 or at most 2 people living there.  If the four bed home only has one occupant, their lighting and hot water use is likely to be less than the EPC estimate.

As a prospective buyer or tenant, you won’t have personally seen the DEA at work, and you have to trust that (s)he did a thorough job of inspecting the property.  However, you don’t have to accept an inaccurate EPC. If you have reason to think that an error has been made you can challenge the DEA, whose accreditation details are given on the EPC.

The rest of the EPC

I’ll consider the meaning of the rest of the EPC in my next blog, and give some ideas of how to use the information it contains.

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More information about EPCs from YouGen

Read part two of our Home buyer and renters' guide to reading an EPC here!

Energy efficiency information page

EPCs should make financial benefits clearer says Consumer Focus

Home seller's guide to buying an EPC: what to consider

What the EPC requirement means for people who want to install solar PV

About the author: @linniR is a consultant, a freelance writer and a Domestic Energy Assessor accredited with the NHER scheme, and she enjoys all three.  She tweets regularly on issues relating to energy efficiency and renewables and provides consultancy, especially in relation to training needs.

If you have a question about anything in the above blog, please ask it in the comments section below.

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9 comments - read them below or add one


MiguelComment left on: 18 August 2015 at 1:52 pm

Great article! it is good to read something about EPCs beyond "an epc is mandatory whenever a house is built, sold or rented".

I also am energy assessor, and I am not really satisfied with the figures shown in the EPC. If the running costs match with the real cost is by accident.

 I think there are too many assumptions to achieve a good match.

Firstly the calculation method. Theoretical values for thermal transmittance of walls, roofs and floors and average climatic conditions usually differ from reality. This is for new built, but existing dwellings still have more assumptions.

Besides, the energy use is really different between householders.

In my experience, simple properties with gas boilers are not bad modeled. When alternative heating systems are used or the property have different extensions built in different dates, the results can be less accurate. 

On the other hand, if we want to have accurate figures, we should conduct a thermal survey of the property, a test for air tightness, etc, and it would be expensive and time consuming.

I think EPCs should be understood as a rough guide about the dwelling energy performance with an idea of where to start to improve it. But if you are thinking about installing some measures you should study the matter further. 

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Linn Rafferty

Linn Rafferty from JTec Energy PerformanceComment left on: 4 September 2013 at 5:26 pm

hello SBChilton, and thanks for your question.

Software can only accept an efficiency figure for a biomass boiler, higher than the default value, where the specific boiler has been added to the database of boilers within the software. Currently, I understand that there are very few biomass boilers included in that database.  

For those boilers that are included, the software is able to use the manufacturer's declared efficiency, rather than that default you mention, but otherwise the default must be used.

To go into the SEDBUK database, the manufacturer has to provide evidence that the efficiency they claim is supported by formal test results. It has to have been tested by an appropriately qualified test lab, as required under the Construction Products Directive. 

It would be good to see some more entries, as you are not the only one who is disatisfied that most biomass fired boilers receive the standard, default efficiency, when at least some of the new boilers must achieve genuinely higher efficiencies than this.   To my mind, the solution is clear - the boiler needs to be included in the database. However, they can't be included unless the manufacturer applies, so the organisation you should turn to is the manufacturer, and you should suggest they apply for inclusion in the SAP product database.

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SbchiltonComment left on: 3 September 2013 at 7:40 pm


i have a similar issue to the one mentioned by Gavin. We removed a 20 year old oil boiler which at peak efficiency cost around 6.8p/kWh to run, and replaced it with a 92% efficient biomass boiler as a result we have seen a massive drop in heating bills without any changes to he fabric of the house - However this has reduced our EPC rating 26 points to a G6. 

My wife and I were really shocked, further digging has revealed that biomass pellet stoves have a generic efficiency rating in SAP of 65% which I think explains the low reading! I'm convinced that the report is incorrect but I don't know where to turn to for further investigation?

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JeremyOlmComment left on: 30 August 2013 at 8:47 am

I bought my first house about 6 years ago in Chelmsford, it was an old terraced house with no insulation, wooden doors and windows that leaked and shook when windy, and wooden floorboards instead of carpets. As you can imagine it was very cold and the heat had plenty of places to escape from.  The energy performance certificate was very helpful in guiding us to what we needed to do to achieve a cosy warm house and lower bills. We insulated the walls and attic, invested in new aluminium windows with double glazing, including the doors, and carpeted the house throughout. Our bills came down dramatically and we are nice and warm now in the winter months.

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Linn Rafferty

Linn Rafferty from JTec Energy PerformanceComment left on: 24 July 2013 at 9:44 pm

hi Gavin

thanks for your question.

It helps to remember that the EPC rating is based on the cost of heating a home, so as well as taking account of the efficiency of the boiler, it allows for the price of the fuel used in the boiler.

Wood pellets are more expensive per kWh of heat delivered than some other fuels, like mains gas & heating oil, so when this is taken into account the overall rating is lowered.  Of course when looking at the environmental rating, the wood pellet boiler would achieve a higher score than either of those two fuels, but it's the cost based score that appears on the front of the EPC and on which the rating band (A to G) is based. All the same, I'm a bit surprised that the home only achieved a G, the lowest rating. 

Perhaps the fabric of the building is very inefficient, eg solid wall without any insulation, no insulation in the roof, a detached build form rather than semi or terrace?  Everything that has a significant effect on the fuel costs, for heating, lighting and providing hot water, is included in the overall efficiency rating, to give a comparison between homes that reflects the fuel cost per square metre of floor area.

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Gavin Smith

Gavin SmithComment left on: 23 July 2013 at 11:36 am

I have a friend who has just installed a biomass pellet boiler in their house.  They thought this was going to boost their EPC rating and installed a boiler with 90.3% rated efficiency.  They are off the gas grid so this should save them money too.


You can imagine thier dissapointment when the EPC showed the biomass boiler at 2 stars for efficiency!  They have ended up with a G rating house.  Why does the EPC show biomass as being so inefficient?  

I think this may relate to Rob Donovan's problem though in this case they had 4 stars for environment.


What do you think Linn?

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Linn Rafferty

Linn Rafferty from JTec Energy PerformanceComment left on: 25 September 2011 at 2:25 pm

Rob - sorry for not replying sooner. I'm surprised that you find that biomass boilers receive a high CO2 rating in the EPC, higher than heating oil or LPG.  A glance at Table 12 of SAP shows that wood pellets are allocated emissions of 0.028 kg CO2 per kWh, whereas the figure for LPG is 0.245 kg CO2 per kWh and oil 0.274 kg CO2 per kWh - approximately ten times higher than biomass.

From these figures, you can see that a biomass boiler would have to be very inefficient and/or unresponsive, or working via a very inefficient/unresponsive system, for its overall emissions to be higher.

Do you have an example you could point me to? 

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greenenergyComment left on: 16 September 2011 at 7:28 am

I just purchased a new home, and I replaced a lot of the lighting with GU10 LED's from I'm also looking at replacing more from Prices have come down so much! and I purchased my new home in 2010!

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Rob Donovan

Rob DonovanComment left on: 26 August 2011 at 10:13 am

I have several clients that now take me along, to view potential properties, if you ask for the EPC report all you ever get sent is the graph, not that helpful,   but the most frustrating thing is as the vendors agent, they have no idea of the construction,cavity walls, insulation levels of the building.

On one viewing they said we use the same logo on all our houses!

I think that the Estate agents should have to trained to realise that this is a very important document, and understand exactly what it means to their clients.

If you are looking to by a property get the full certificate (5-6 page document) read it carefully it will tell you wall construction and basic insulation levels.

 Linn, What are your thoughts on how badly the EPC software performs when you ask it include a Biomass boiler?

we have found that it comes out with a very high co2 rating even higher than that of heating oil or LPG, this is then incorrect and very misleading to the client.

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