EPC calculations and how it impacts your property’s score
Energy Performance Certificates (EPCs) remain a critical requirement for homeowners, landlords, letting agents, and property investors across the UK. With the introduction of updated EPC conventions and modelling changes over the last year, many properties are seeing noticeable differences in their EPC scores—even when no physical improvements have been made.
If you are planning to sell, let, refinance, or improve your property, understanding how these new conventions affect your EPC rating is essential.
In this guide, we explain how changes to RdSAP conventions now influence points for windows, floors, heating systems, hot water, and electric appliances.
Why EPC Conventions Change
EPC assessments in England and Wales use a methodology called Reduced Data Standard Assessment Procedure (RdSAP).
Conventions are periodically updated to ensure assessors record properties more accurately and consistently. These updates often change how features are interpreted in the software, which can alter the final EPC score.
Recent updates have particularly impacted:
- Window assessment rules
- Solid floor assumptions
- Electric showers and hot water usage
- Heat pump modelling
- Electric underfloor heating
- Heating fuel comparisons
These adjustments can either increase or decrease your EPC score depending on the property setup.
1. Windows – Updated Assumptions Can Change EPC Points
Windows play a significant role in heat loss calculations.
Under newer conventions, assessors must be more precise when identifying glazing types.
Key changes
- If evidence of double glazing cannot be confirmed, the software may default to single glazing assumptions.
- Older double glazing may no longer automatically receive modern performance values.
- Window age and installation evidence matter more than before.
EPC Impact
This can affect several SAP points because glazing influences:
- Heat loss
- Energy demand
- Heating costs
For landlords and property owners, this means older double glazing may not score as well as previously assumed.
2. Solid Floors – More Conservative Heat Loss Calculations
Many UK homes—especially Victorian terraces and older properties common across Liverpool, Southport and West Lancashire—have solid ground floors.
Recent conventions tightened assumptions regarding:
- Floor insulation
- Floor construction
- Unknown insulation levels
EPC Impact
If insulation beneath a solid floor cannot be verified, the software may assume no insulation present, which increases heat loss.
This can reduce the EPC rating slightly, especially in ground floor flats or older houses.
3. Electric Showers and Hot Water Demand
Electric showers have become more common in modern refurbishments and rental properties.
However, EPC modelling often penalises electric hot water systems because electricity has a higher carbon factor and higher assumed cost than gas.
Key EPC Effects
Electric showers:
- Increase electricity demand
- Increase hot water energy consumption
- Can reduce the overall EPC rating
In contrast, gas heated hot water systems tend to score more favourably.
This is why some properties with electric-only systems struggle to reach EPC band C.
4. Gas Heating vs Electric Heating
One of the biggest influences on EPC scores is fuel type.
Traditionally, EPC models favour mains gas heating systems because they are cheaper per kWh than electricity.
Typical EPC Impacts
Gas boilers often score well because:
- Lower fuel costs
- Efficient condensing boiler assumptions
- Lower running cost modelling
Electric heating systems can sometimes reduce EPC scores due to:
- Higher electricity cost assumptions
- Lack of heat storage
- Higher carbon factors
However, the picture is changing as the government pushes toward electric heat pumps and low-carbon heating.
5. Heat Pumps – Better EPC Scores Than Older Electric Systems
Air source heat pumps are increasingly common due to:
- Government incentives
- The Boiler Upgrade Scheme
- Net zero targets
Unlike traditional electric heating, heat pumps can significantly improve EPC ratings because they operate with high efficiency.
Why Heat Pumps Score Well
Heat pumps typically deliver 300–400% efficiency, meaning they produce far more heat energy than electricity consumed.
This can lead to:
- Lower energy demand
- Improved EPC ratings
- Better environmental scores
For landlords aiming for future EPC C targets, heat pumps may become a viable upgrade.
6. Electric Underfloor Heating – Often Scores Poorly
Underfloor heating powered by electricity is popular in:
- Bathrooms
- Kitchens
- Renovated flats
However, from an EPC perspective it is usually considered direct electric resistance heating, which is less efficient than gas systems.
EPC Implications
Electric underfloor heating may:
- Increase electricity consumption
- Reduce EPC points
- Be treated as secondary heating
Unless paired with a heat pump system, electric underfloor heating rarely improves EPC scores.
What This Means for Homeowners and Landlords
Because of these convention changes, many property owners are surprised when:
- Their new EPC rating differs from an older certificate
- Improvements do not increase the score as expected
- Electric heating systems reduce the rating
This is why having an experienced Domestic Energy Assessor is essential.
A qualified assessor will ensure:
- Features are recorded correctly
- Evidence is used where possible
- The most accurate EPC rating is produced.
Need an EPC in Southport, Liverpool, Ormskirk, Skelmersdale, Burscough or Scarisbrick?
If you are selling, renting, refinancing or improving your property, obtaining an up-to-date EPC is essential.
At Eden Energy Solutions, we provide:
✔ Fast EPC assessments
✔ Fixed fee EPCs for properties up to 4 bedrooms
✔ Professional domestic energy advice
✔ Coverage across Southport, Liverpool, Sefton, and West Lancashire
Understanding how the latest EPC conventions affect your property can help you make smarter decisions about upgrades and compliance.
📞 Book your EPC today with Eden Energy Solutions
01704 651769 / 07312274390
Visit:
www.edenenergy.uk
Contact us to arrange a fast local assessment.