How Much Does A New Boiler Improve EPC Rating?

epc ratings new boilers

Replacing a low efficiency boiler with a high efficiency boiler can improve the epc rating by up to 8 sap points.

In this case we’ll first look at gas boilers. We’ll also look at different types of boilers such as electric boilers, lpg boilers and oil boilers.

Boilers have different efficiencies but generally fall into 3 bands.

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1. Low efficiency boilers

These have an efficiency of around 65%. These are usually old boilers that are over 30 years old and would typically have permanent pilot lights and open flues or balanced flues.

glow-worm ep 80f boiler

2. Medium efficiency boilers

These have an efficiency of around 79%. These boilers are usually more than 20 years old. They have automatic ignition pilot lights but are non condensing.

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3. High efficiency boilers

These have an efficiency of between 88% – 90%. Since 2005 it became legislation that all new boilers fitted had to be condensing boilers.

The Main Factor That Will Determine If And How Much The Rating Will Change

The EPC rating will change depending of the efficiency of the previous boiler being replaced

Changing a boiler from one with an efficiency of only 69% to over 88% can improve your epc rating by around 8 sap points.

Changing a boiler from a medium efficiency boiler of 79% to one of over 88% can improve your epc rating by around 4 sap points.

Changing a boiler from a modern condensing boiler of over 88% efficiency to another condensing boiler of over 88% efficiency, will produce no improvement in the EPC rating. This is because the EPC is not a condition report and will always use the manufactured efficiency of the boiler even if it is faulty or not working because an assumption is being made that it can always be fixed.

Why Are Condensing Boilers More Efficient

Condensing boilers are more efficient because they capture and reuse heat that would otherwise be lost.

They cool exhaust gases to recover extra heat, leading to higher energy conversion. This reduces fuel consumption, lowers costs, and meets energy regulations.

Condensing boilers are a cost-effective and eco-friendly choice for heating systems.

Changing A Boiler To A Different Fuel Source

The efficiency of the boiler itself is only one part of the epc rating equation. The fuel source and the cost of that fuel also plays a very important part in the EPC rating.

The table shows the comparison cost of different fuels per KWH to heat a home.

Comparison heating costs of different fuel types

Most Expensive
Least Expensive
Fuel Type
Electricity Standard
Mains Gas
Cost per KWh (pence)

These costs are assuming a boiler efficiency of 90% except for electricity which has an efficiency of 100%.

Source: Nottingham Energy Partnership fuel comparison December 2023

In the past, heating a typical UK three-bedroom semi-detached home with oil has generally been pricier compared to using gas. However, recent significant events, such as the Covid-19 pandemic, the Russian-Ukraine conflict, and the ongoing cost of living challenges, have introduced even more volatility into the prices of both gas and oil.

As of April 2023, in alignment with the UK Government’s Energy Price Guarantee, the cost per kWh of heating oil is now more economical than that of gas, according to The Energy Savings Trust report.

So if you are changing a boiler to a more expensive fuel source it is likely to result in a lower rating EPC even if the efficiency of the new boiler is better.

In a seperate article we show a case study showing the impact of changing the fuel source to an electric boiler.

Additional Ways to Improve Your EPC Rating

Enhancing your home’s energy efficiency with energy-efficient lighting can result in a higher EPC rating. Additionally, investing in loft and wall insulation contributes significantly to better energy performance. Upgrading to double or triple glazing windows offers another effective way to positively impact your property’s EPC rating.

These improvements not only lower energy costs but also minimise heat loss, ultimately leading to a more favourable EPC report. By focusing on insulation and lighting upgrades, you unlock much potential for a higher rating and reduced heating costs.

Switching to Energy-Efficient Lighting

Switching to energy-efficient lighting reduces a property’s energy consumption and contributes to lower energy costs and a smaller carbon footprint. It is the simplest energy improvement to carry out.

Most of the energy efficient lighting these days are LED and they have significantly reduced in price over the years.

Low energy lights can improve the epc, even though it is not one of the major improvements that can be made. It can improve the EPC rating by 2 sap points if you went from zero low energy lights to 100% low energy lighting.

The Benefits of Loft and Wall Insulation

Most of a property’s heat is lost through the walls and roof. According to the Energy Savings Trust, a quarter of heat is lost through an un-insulated roof and around a third of heat is lost through un-insulated walls.

So reducing wasted heat loss through the walls and roofs always pays big dividends resulting in reduced energy bills, lower carbon emissions and higher EPC ratings.

The EPC will always show insulation as one of the top recommendations and can result in up to 8 point improvement in the EPC sap rating.

Loft insulation is always a top priority in improving EPC ratings and reducing energy bills due to its relatively low cost of installation, high energy savings and its quick payback time.

Upgrading Windows to Double or Triple Glazing

If you have single glazed windows, then upgrading to double of even triple glazing will improve the energy rating.

Like low energy lights, double glazing will not raise the rating as much as most people think. To go from single glazed window to double glazed windows will improve the rating by 3 points.

A further 1 sap point can be gained if you upgrade to triple glazed windows or if you are able to provide documentary evidence that your double glazed windows have a u-values of 1.4 W/m2K or lower.

Smart Meters and Their Impact on EPC Rating

Smart meters have no impact on the rating of an EPC. However, by installing smart meters, property owners can access real-time data on energy usage, providing insights that lead to better understanding of a property’s running costs.

These meters also help identify areas of energy wastage, contributing to an overall improvement in lowering the energy costs of a home.


A new boiler can improve epc ratings if it has a higher efficiency rating than the one it is replacing.

The fuel source also plays a role in determining the final rating.

By understanding how these factors work together can assist you in making informed decisions in ways to lower your energy bills which also will raise the epc rating of the property.


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Rickie Dickson
Written by Rickie Dickson

Rickie Dickson is an experienced and qualified domestic and non domestic energy assessor. He helps homeowners and businesses in all matters relating to energy efficiency, from meeting building regulations compliance to improving a property’s energy rating score.