If you need an Energy Performance Certificate, an EPC assessor is the person who visits the property, records how it’s built and heated, and produces the rating.
In practice, they’re there to answer one question: how energy-efficient is this home, based on its construction, insulation, windows, heating system, and fixed features?
Here’s what they actually look at, how the visit works, and what you get at the end.
What is an EPC assessment?
An EPC assessment is a survey of a property’s energy performance.
A qualified assessor visits the home, records the features that affect energy use, and produces a certificate rating it from A (most efficient) to G (least efficient).
The certificate also includes recommended improvements, upgrades that could raise the rating, with estimated costs and savings.
In England and Wales, a valid EPC is usually required when a property is sold or rented. Certificates last 10 years.
What does the assessor inspect?
The assessor is not judging décor, cleanliness, or general presentation. They’re recording the physical features that affect heat loss and energy efficiency.
During the visit, they’ll usually look at:
- Walls — what they’re made of and whether they’re insulated
- Roof and loft — roof type and any visible loft insulation
- Windows — single, double, or triple glazing, and approximate age
- Doors — external doors and relevant draught proofing features
- Heating system — boiler type, fuel source, and heating setup
- Heating controls — programmer, room thermostat, TRVs, smart controls
- Hot water — how it’s heated and whether any cylinder is insulated
- Lighting — how much of the fixed lighting uses low-energy bulbs
- Renewables — solar panels, heat pumps, or other installed systems
- Floor construction — where this can be identified
- Extensions — if parts of the property were built differently from the original home
They may also take measurements and photographs to support the inputs used in the assessment.
That matters because where evidence is missing, the methodology may require assumptions. The better the evidence, the more accurate the result.
On-site vs desktop assessments
A proper EPC assessment is normally done with a physical visit.
Some providers also advertise desktop or remote assessments. These rely more heavily on existing records, photographs, or information supplied by the owner.
The risk is that homeowners often don’t know details like insulation type, construction method, or heating specifications. Where those details can’t be evidenced, assumptions may be used and those assumptions are not always favourable.
If you’re getting an EPC for a sale, a letting, or to decide which upgrades are worth doing, an on-site assessment is usually the better option because the assessor can record what is actually there rather than relying on guesswork.
What they don’t inspect
An EPC assessment is not a building survey.
The assessor will not usually:
- inspect the structural condition of the property
- diagnose damp, subsidence, or movement
- test the boiler or heating system
- inspect electrics or plumbing
- move furniture, lift floorboards, or open up the building
They’re assessing energy performance, not the overall condition of the home.
How long does it take?
Most EPC visits take around 20 to 60 minutes.
A small flat may take less time. A larger or more complex house, especially one with extensions or unusual construction, may take longer.
The assessor will usually need access to all rooms, and ideally the loft and boiler as well.
How to prepare
You don’t need to do much, but a bit of preparation helps.
Before the visit:
- make sure the assessor can access all main rooms
- clear access to the loft hatch if possible
- know where the boiler is
- have any useful paperwork ready, such as boiler documents, insulation certificates, or window installation paperwork
This can help the assessor record the property more accurately and reduce the need for assumptions.
How the rating is calculated
After the visit, the assessor enters the information into approved software.
For existing homes, the rating is based on RdSAP, the Reduced Data Standard Assessment Procedure. This is a standardised method for assessing the energy performance of dwellings.
It does not use your actual energy bills. It measures the property’s likely performance under standard assumptions.
The result is a score from 1 to 100, which maps to the EPC bands:
- A: 92–100
- B: 81–91
- C: 69–80
- D: 55–68
- E: 39–54
- F: 21–38
- G: 1–20
What do you get at the end?
After the assessment, the certificate is lodged on the national EPC register.
You receive:
- the EPC certificate, showing the current rating and potential rating
- a recommendations report, listing measures that could improve the score
- an environmental impact rating, showing estimated carbon emissions
The recommendations section is often the most useful part. It gives you a property-specific starting point for improvements rather than generic energy-saving advice.
How much does it cost?
EPC assessments typically cost around £60 to £120, depending on the size, type, and location of the property.
Larger or more complex homes may cost more.
Who can carry out an EPC assessment?
Only an accredited Domestic Energy Assessor (DEA) can produce a valid domestic EPC.
They must be registered with an approved accreditation scheme and follow the required methodology.
When choosing one, it’s worth looking for an assessor who carries out a full on-site visit and has experience with your type of property, especially if it’s older, unusual, or non-standard construction.
When do you need one?
A valid EPC is usually needed:
- before marketing a property for sale
- before marketing a property for rent
- once an existing certificate has expired
If you already have a valid EPC, you do not normally need a new one straight away.
But if you’ve made improvements, for example new insulation, a new boiler, or solar panels, a fresh EPC can show the updated rating and potential improvements more accurately.