How is your EPC rating calculated? (And how to check yours for free)

If you’ve bought or sold a property, it’ll most likely have an EPC. But how is it calculated?

First off, what is an EPC rating?

An Energy Performance Certificate (EPC) is a guide to how energy efficient a property is. It includes estimated energy costs and a rating (or band).  Bands range from A to G, with A being the most energy efficient. The average EPC rating in the UK is D.

How is an EPC rating calculated?

An EPC rating is based on how much energy your property uses per square metre (eg for heating, light and so on) and how much energy it loses (eg through poor insulation). The assessor will first calculate the property’s Standard Assessment Procedure (SAP) score and then use that to determine the EPC rating. A higher SAP score = a better EPC rating.

How is the SAP score calculated?

To work out the SAP score, the EPC assessor will look at all the ways that your property uses and loses energy. There’s a very long list to check. For example, they’ll look at how energy efficient the heating system is, how well the property is insulated, what energy source is used (electric, gas, oil etc), what type of shower you have and whether the property has any renewable energy technologies installed. These results will then be used to calculate the property’s overall SAP score.

Your home’s SAP score will usually be between 1 and 100. A score of 100 means that there is no energy cost. So, only properties that generate more energy than they use are given a score over 100.

How accurate are EPC ratings?

Most elements of the EPC are based on facts, such as whether you have single, double or triple glazing. However, the assessor might have to make a few estimates, based on the age and condition of the property. Nevertheless, EPC ratings are very accurate, as long as the assessor records everything correctly.

But do EPC ratings really matter?

Well yes, if you want to save money on your energy bills. A home with an EPC rating of C will pay around £750 a year less on energy than one with an E rating.

Energy efficiency is also crucial if you want to help tackle the climate crisis. (26% of the UK’s greenhouse gas emissions come from homes.)

Of course, your EPC rating is only part of the story. Your energy use will depend on a range of things, from how long you have the heating on each day to how often you use your washing machine. But your home’s energy efficiency plays a big role.

And EPCs are particularly important if you’re a landlord, as all private rented properties legally need to have a minimum E rating. And the rules on EPCs for landlords are potentially set to get a whole lot stricter.

How to find your EPC rating for free

No idea what your home’s EPC rating is? You can check it for free using our handy EPC tool. And the tool doesn’t just tell you the current EPC rating, it’ll also let you know when the property was last assessed. Plus, it’ll tell you what rating your home could achieve if you carried out some improvements.

How to get an Energy Performance Certificate

EPCs are only valid for 10 years. For a new EPC, you’ll need to book a domestic energy assessment. If you’re in England, Wales or Northern Ireland, you can find your nearest energy assessors here. If you’re in Scotland, you can get a list of energy assessors here.

How to improve your EPC rating

Your EPC certificate will recommend some things you can do to improve your rating (and to reduce your energy bills). You’ll probably want to tackle the quickest and easiest options first, such as installing loft insulation and fixing draughts.

After that, you might want to look at renewable energy solutions, such as solar panels or an air source heat pump, as well as retrofitting your home by upgrading windows, switching to an energy efficient boiler, installing cavity wall insulation and so on.

Get a personalised Green Home Plan

Try our new Green Home Plan tool to find out how you can improve your home's energy efficiency with specific, personalised recommendations. See how much you could save on both energy bills and carbon emissions.

Tandem Marketplace provides access to tools, advice and a range of greener home improvement products through our marketplace partners. All helping you to cut down your bills and your carbon footprint.


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