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Why Are Gas Boilers A-Rated but Electric Boilers D-Rated?
Last Updated on September 18, 2026 by daxom
Why Are Gas Boilers A-Rated While Electric Boilers Get a D? Understanding the SAP & EPC Puzzle
If you have ever checked an Energy Performance Certificate (EPC) and wondered why a gas boiler can contribute to a high EPC rating while an electric boiler can result in a lower rating, you are not alone.
At first glance, it seems confusing.
A modern electric boiler can convert virtually all of the electricity it uses into heat at the point of use. It produces no combustion emissions inside the property. Yet an electric heating system can sometimes receive a less favourable EPC outcome than a gas boiler.
So, why can a gas boiler score better than an electric boiler on an EPC?
The answer lies largely in how EPCs are calculated using the Standard Assessment Procedure (SAP).
An EPC rating is not simply a measurement of how efficiently a boiler produces heat. The calculation considers a range of factors, including the building’s construction, insulation, heating system, controls and modelled energy costs.
This can produce results that appear surprising if you look only at the efficiency of the heating appliance itself.
In this guide, we explain why electric boilers can receive lower EPC ratings, how SAP calculations affect the result, and what EPC reform could mean for electric heating.
What Is an EPC Rating?
An Energy Performance Certificate (EPC) provides an assessment of a property’s energy performance.
Properties are given an energy efficiency rating from A to G, with A representing the highest rating and G the lowest.
EPCs can be relevant when a property is being sold or rented, and they can also influence decisions around energy improvements, financing and heating upgrades.
However, an EPC rating should not be interpreted as a simple measurement of the efficiency of a particular boiler.
The rating is produced using a standardised calculation methodology.
That distinction is important when comparing gas boilers, electric boilers, heat pumps and other heating technologies.
How Does SAP Affect an Electric Boiler’s EPC Rating?
The Standard Assessment Procedure (SAP) is the methodology used to assess the energy performance of buildings for EPC purposes.
SAP takes account of factors including:
- Property construction
- Insulation
- Windows and doors
- Heating systems
- Heating controls
- Hot water
- Ventilation
- Renewable technologies
- Modelled energy use
- Modelled energy costs
This means an EPC is assessing the property as a whole, rather than simply asking how efficiently a boiler converts energy into heat.
An electric boiler can therefore have very high efficiency at the point of use while the property’s overall EPC rating is affected by other aspects of the SAP calculation.
In simple terms:
EPC rating ≠ boiler efficiency alone.
This is one of the most important points to understand when comparing electric and gas heating.
Why Can Gas Heating Score Better Than Electric Heating?
One important factor is the modelled cost of energy used within the EPC methodology.
Historically, electricity has generally had a higher unit cost than mains gas in the UK.
Consequently, a property using electricity for heating can sometimes have higher modelled running costs within an EPC calculation than a similar property using gas.
That can affect the property’s overall EPC score.
However, this does not mean that a gas boiler is automatically more efficient than an electric boiler.
Instead, the EPC is produced using a standardised methodology that considers several factors, including energy costs.
This is why it is important not to interpret an EPC rating as a direct ranking of heating appliance efficiency.
Electric Boiler Efficiency vs EPC Rating
Electric boilers are often described as being close to 100% efficient at the point of use because virtually all of the electrical energy entering the appliance is converted into heat.
But appliance efficiency and EPC performance are different measurements.
An EPC calculation considers the energy required to operate the property and applies the assumptions and methodology used within SAP.
As a result, a highly efficient electric boiler does not automatically guarantee a high EPC rating.
Other factors can also influence the result, including:
- The property’s insulation
- Heat loss
- Heating controls
- Hot-water requirements
- Energy prices used in the calculation
- The type of electric heating system
- Renewable energy technologies
- The SAP methodology being used
Does a Low EPC Rating Mean an Electric Boiler Is Inefficient?
No.
A lower EPC rating does not automatically mean that an electric boiler is inefficient or that the heating system is performing badly.
The EPC is a standardised assessment of the property.
If you have electric heating, it is useful to consider other information alongside the EPC, including your property’s actual energy consumption and heating performance.
Actual energy consumption
Look at how much electricity the property actually uses over time.
Energy bills
Your real energy costs can provide useful information about household expenditure alongside the modelled figures shown on an EPC.
Comfort
A heating system should provide adequate and controllable heat throughout the property.
Insulation and heat loss
Improving the building fabric can reduce the amount of energy required to heat a property, regardless of the heating technology being used.
Carbon impact
The carbon impact of electric heating also depends on how electricity is generated. As the electricity grid changes, the carbon intensity associated with electricity can change too.
Why Do EPC Ratings Matter to Homeowners?
An EPC is more than a document that sits in a drawer.
Energy ratings can be relevant when a property is:
- Bought or sold
- Rented
- Renovated
- Improved for energy efficiency
- Considered for certain finance or funding schemes
This makes the way different heating technologies are represented within EPC calculations increasingly important.
A homeowner investing in insulation, solar panels, electric heating or other energy improvements naturally wants the EPC methodology to provide a useful representation of the property’s performance.
Are EPC Ratings Changing?
The government has been considering reforms to the EPC system as part of wider changes to how building energy performance is assessed.
One area of discussion has been whether a single headline EPC rating provides enough information for homeowners and other users.
A broader approach could provide separate information about different aspects of building performance, potentially including:
Fabric Performance
How effectively the building retains heat.
This can include factors such as insulation and heat loss.
Heating System Performance
Information about the property’s heating system and its performance.
Smart Readiness
How well a property can work with technologies such as smart controls, batteries, electric vehicle charging and flexible energy tariffs.
Energy Cost
An indication of the modelled energy costs associated with operating the property.
Providing several measures could give homeowners more information than relying on a single A-to-G rating.
Important: EPC methodology and government proposals can change. Homeowners and installers should check the latest official guidance when making decisions based on EPC requirements.
Why a Single EPC Letter Doesn’t Tell the Whole Story
Consider two homes.
One has a gas boiler and receives a high EPC rating.
Another uses electric heating and receives a lower rating.
It would be easy to assume that the first heating system is automatically more efficient or environmentally friendly.
But that conclusion does not necessarily follow from the EPC rating.
The rating is the result of a calculation involving multiple inputs and assumptions.
A more complete assessment should consider:
Cost: How much does the property cost to heat?
Energy consumption: How much energy does it use?
Carbon: What are the associated emissions?
Fabric: How effectively does the building retain heat?
Heating performance: How effectively does the heating system provide the required heat?
Looking at these factors together provides a more complete picture of a property’s energy performance.
What Does This Mean for Electric Boiler Owners?
If you have an electric boiler and are concerned because your property has a relatively low EPC rating, there is no reason to assume that the boiler itself is necessarily the problem.
Instead, look at the EPC recommendations and consider the property as a whole.
Potential improvements can include:
- Improving insulation
- Reducing heat loss
- Upgrading heating controls
- Improving hot-water efficiency
- Installing renewable technologies where appropriate
- Reviewing energy consumption
- Choosing a heating system appropriate for the property
The right approach will depend on the building, its heating requirements and the homeowner’s objectives.
What Does This Mean for Heating Installers?
For heating installers, EPCs can sometimes create confusion for customers considering electric heating.
A customer may see a lower EPC rating and assume that an electric boiler is inefficient.
Installers can help by explaining the difference between:
Appliance efficiency
and
EPC methodology.
These are not the same measurement.
It is also important to explain that an EPC uses a standardised calculation rather than measuring exactly how much energy an individual household will use.
Clear communication can help customers understand what their EPC tells them — and what it does not.
Electric Boilers, Heat Pumps and the Future of Heating
The UK’s heating market is changing as electrification and low-carbon heating technologies become increasingly important.
Electric boilers and heat pumps are different technologies and should not be treated as interchangeable.
A heat pump moves heat from the environment into a building and can therefore deliver more heat energy than the electrical energy it consumes under suitable operating conditions.
An electric resistance boiler, by comparison, converts electrical energy directly into heat.
Both use electricity, but their operating principles and performance characteristics are different.
Understanding these distinctions is important when discussing EPC ratings, energy consumption, running costs and carbon emissions.
The Future of EPC Ratings
As heating technology changes, the way building performance is measured becomes increasingly important.
A system designed around historical energy costs may not provide the same picture as one designed to show a broader range of factors, including building fabric, heating performance, energy use and smart technology.
For homeowners, the key is to understand what the EPC is actually measuring.
For installers, it is important to explain the difference between an EPC rating and the real-world performance of a heating system.
And for policymakers, the challenge is ensuring that building performance information remains useful as the UK’s energy system changes.
The Bottom Line: Look Beyond the EPC Letter
So, why can a gas boiler receive a better EPC outcome than an electric boiler?
The answer is not simply that the gas boiler is more efficient.
EPC ratings are produced using the SAP methodology, which considers a range of factors, including the property’s characteristics, heating system and modelled energy costs.
As a result, an electric boiler can be highly efficient at the point of use while the property still receives a less favourable EPC rating.
That is why the EPC letter should be viewed as one piece of information rather than the complete story.
For homeowners and installers, it makes sense to consider energy consumption, running costs, building performance, heating technology and carbon emissions alongside the EPC rating.
A single letter cannot tell you everything about how a home heats, how much energy it uses or how its heating system performs.
Frequently Asked Questions
Why can an electric boiler have a low EPC rating?
An electric boiler can contribute to a lower EPC rating because the EPC calculation considers more than the boiler’s point-of-use efficiency. Factors such as the property’s characteristics, heating system and modelled energy costs can all affect the final rating.
Are electric boilers 100% efficient?
Electric resistance boilers can convert virtually all of the electricity they consume into heat at the point of use. However, this appliance efficiency should not be confused with the overall energy or carbon performance of a property.
Is a gas boiler more efficient than an electric boiler?
It depends on what is being measured. A gas boiler and an electric resistance boiler use different energy sources and technologies. An EPC rating also considers factors beyond the appliance’s conversion efficiency, so the EPC letter alone cannot be used as a direct comparison of boiler efficiency.
Why does gas sometimes score better than electricity on an EPC?
The SAP methodology includes modelled energy costs, among other factors. Where electricity has a higher assumed cost than gas, this can affect the calculated EPC result for properties using electric heating.
Does a low EPC rating mean my electric boiler is bad?
No. A low EPC rating does not automatically mean that the electric boiler itself is inefficient or faulty. The rating reflects the property under a standardised assessment methodology.
Can an electric boiler improve my EPC rating?
Potentially, but the result depends on the property and the complete SAP calculation. Improvements to insulation, heating controls, renewable technologies and other aspects of the property can also affect EPC performance.
What is SAP?
SAP stands for Standard Assessment Procedure. It is the methodology used to assess the energy performance of buildings for EPC purposes in England and Wales.
Will EPC ratings change in the future?
EPC reform has been under consideration, including proposals to provide more detailed information about different aspects of building performance rather than relying solely on a single headline rating. The exact requirements and implementation should be checked against the latest government guidance.
