Will New Windows Improve My EPC Rating? (With Real Point Gains)

Yes, replacing old windows with new A-rated units almost always improves an EPC rating, usually by several points and sometimes by a full band if the old windows were single glazed. The gain comes from a big drop in U-value, the measure of how much heat a window loses, and the EPC assessment rewards that directly. How many points you get depends on what you start with, how much window area the house has, and what else the assessment picks up. You can see our energy rated range on the casement windows page.

We fit windows across Caerphilly, Cardiff and the wider Valleys, so we see the before and after on real EPCs. Below we explain how the assessment scores windows, the U-values you are moving between, the realistic point gains, guide costs against savings, and what Part L and the landlord MEES rules mean for you. Two worked examples show how the numbers land on typical local homes.

Key takeaways

• New A-rated windows cut the U-value sharply, and the EPC rewards that with points.
• Old single glazing sits near 5.0 W/m2K, 1990s double glazing around 3.1, and A-rated units around 1.2.
• Typical gains run from a few points to a full band, biggest when replacing single glazing.
• WER A is the entry energy rating and A+ is higher; both are strong for an EPC.
• Part L 2022 sets 1.4 W/m2K as the limit for replacement windows, and we register with FENSA.
• Landlords must usually meet at least EPC E under MEES, and new windows can help get there.

Will new windows actually raise my EPC rating?

In most cases yes. The EPC is a modelled score out of 100 that reflects how energy efficient the building is, and windows are one of the inputs. Swap draughty single glazing or tired early double glazing for modern A-rated units and the model sees a lower heat loss, which pushes the score up.

The size of the jump depends on your starting point. A house in Llanishen with original single glazing will gain far more than a 2005 home in Rhiwbina that already has reasonable double glazing. Windows rarely move an EPC on their own from the bottom band to the top, but they are usually one of the most visible improvements an assessor can record, and they pair well with loft and heating upgrades.

How does the EPC calculation score windows?

An EPC is produced using the government SAP methodology, or its reduced version for existing homes. The assessor records the window type, the glazing, the frame and the age, and the software converts that into a heat loss figure for the whole house. Lower heat loss means a lower predicted energy cost, which is what the A to G rating reflects.

This is why the U-value matters so much. The lower the U-value, the less heat escapes per square metre, and the better the score. It is also why a home with a lot of glazing gains more from new windows than a home with small windows, because the improvement applies across more area.

• The assessor logs glazing type, frame, gap and age.
• SAP converts that into whole house heat loss.
• Lower U-value and more window area means a bigger EPC gain.

What U-values are we comparing, old versus new?

The clearest way to see the gain is to line up the U-values, measured in W/m2K, where lower is better. Old single glazing loses heat at roughly 5.0 W/m2K. Early double glazing from the 1990s sits around 3.1. A modern A-rated window with low-E glass, argon fill and a warm edge spacer comes in around 1.2.

Moving from 5.0 to 1.2 is a large reduction in heat loss per square metre, which is why replacing single glazing gives the biggest EPC jump. Moving from 3.1 to 1.2 is still a solid improvement and usually worth doing, though the point gain is smaller because you were starting from a better place.

• Single glazing: around 5.0 W/m2K.
• 1990s double glazing: around 3.1 W/m2K.
• Modern A-rated double glazing: around 1.2 W/m2K.

How many EPC points can new windows add?

There is no single fixed number, because it depends on the house, but some patterns hold. Replacing single glazing with A-rated units often adds several points and can be enough to lift a home by a band, especially on a small terrace with a high ratio of glass to floor area. Replacing 1990s double glazing typically adds a smaller number of points, because the starting heat loss was already lower.

The honest framing is this: windows are a reliable contributor, not a magic wand. On a home that is close to a band boundary, a set of new windows can be the change that tips it over. On a home sitting mid band, windows help but you may need to pair them with insulation or heating measures to move the letter. We will give you a realistic view at survey, not an inflated promise. Our guide on why a conservatory runs too hot or too cold covers the same U-value logic for glazed rooms.

What does it cost, and what will I save?

As a guide, replacement A-rated casement windows start from around 500 to 900 pounds per window fitted, depending on size, style and glazing, so a typical three bedroom house lands in the low thousands for a full set. That is a real investment, and it is fair to be clear that the energy saving alone will not pay it back quickly.

The value shows up in three ways together: lower heating bills, a warmer and quieter home, and a better EPC that helps at sale or let. For a landlord chasing a compliance band, the EPC uplift can be the main driver. You can compare styles on the main windows hub, and if you want a different opening style our tilt and turn windows carry the same energy ratings.

What do WER A and A+ ratings mean?

The Window Energy Rating, or WER, is a simple A to G label a bit like the one on a fridge. It combines the heat lost through the window with the useful solar heat gained and the air leakage, into one letter. WER A is the strong entry level for a modern window and A+ is a step higher again.

For an EPC, an A or A+ rated window signals low heat loss and scores well. You do not need to chase the very top rating in every room to get a good result, but specifying at least WER A across the house is a sensible baseline. We fit A-rated as standard and can quote A+ where it earns its place, for example on an exposed elevation in the Valleys.

Does Part L 2022 apply to replacement windows?

Yes. Under Part L 2022, replacement windows in an existing home must meet a minimum standard, and the limit for a replacement window is a U-value of 1.4 W/m2K, or a WER of band B or better. In practice the A-rated units we fit are comfortably inside that, so compliance is straightforward.

The work is notifiable, which means it has to be signed off. We are FENSA registered, so we self certify the installation against Building Regulations and your FENSA certificate is issued automatically. You will need that certificate when you sell or remortgage, so keep it safe. This trust and paperwork side matters, which is why our guide on deposit protection and guarantees is worth a read before you choose any installer.

What about landlords and MEES?

If you let a property, the Minimum Energy Efficiency Standards, or MEES, matter. The current rule is that most rented homes in England and Wales must reach at least EPC band E to be let lawfully, with limited exemptions. A property stuck at F or G cannot usually be let until it improves.

New windows are one of the clearer ways to move a poor EPC upward, particularly where the property still has single glazing. For a landlord in Barry or Caerphilly weighing which measures to fund first, replacing the worst windows often gives a visible EPC gain and a more lettable, warmer home in one job. We can prioritise the rooms that will move the score most.

Do new windows stop condensation and draughts?

They usually cut both. Condensation forms when warm moist air meets a cold surface, and old single glazing gives a very cold surface for it to form on. A modern A-rated unit keeps the inner pane much warmer, so surface condensation on the glass drops sharply, though you still need to ventilate the room to manage humidity.

Draughts come from worn seals and poor frames. New windows with fresh gaskets and multi-point locking close the gaps, which both improves comfort and helps the airtightness side of the EPC. The same warmth logic applies to doors, so if you are also weighing a garden door our guide on whether bifold doors feel cold in winter is a useful companion. If you would like a figure for your own home, book a free survey and we will take a look.

Do new windows on their own move the EPC, or do you need the walls and loft too?

New windows move the EPC on their own, but they work hardest alongside loft and wall insulation. The assessment looks at the whole thermal envelope, so a home in Llanishen or Rhiwbina with a warm loft and old single glazing will often see the biggest single jump from the glazing, because that is the weakest point left.

If your walls and loft are already sorted, A-rated casement windows are usually the next best value upgrade per pound. If they are not, we will say so, because it is your money and there is no sense selling you windows to fix a problem that is really coming from an uninsulated loft. Our surveyor gives you the honest order of works at the free visit.

Worked examples

Worked example: a single glazed terrace in Cardiff

A landlord in a Cardiff terrace had original single glazing throughout and an EPC stuck near the bottom of band E. The windows were losing heat at roughly 5.0 W/m2K. We fitted A-rated casement windows at around 1.2 W/m2K across the whole house and registered the work with FENSA.

On the reassessment the improved glazing was recorded across a high ratio of window area to floor space, and the score moved up several points, comfortably clearing the MEES band E threshold with room to spare. The tenant also reported far less condensation on cold mornings, which was a welcome bonus for the landlord.

Worked example: a 1990s semi in Caerphilly

A family in Caerphilly had tired 1990s double glazing around 3.1 W/m2K and a mid band D EPC. They wanted lower bills and a warmer front room, not a band change in particular. We fitted A-rated windows at around 1.2 W/m2K.

The EPC gained a few points rather than a whole band, which is what we predicted at survey, because the old glazing was already reasonable. The bigger win for them was comfort: warmer glass, fewer draughts and a quieter room facing the road. We were clear from the start that this was a comfort and bills upgrade more than a band jump.

Help with the cost is limited in Wales. Our guide to grants for windows and doors in Wales explains what Nest and ECO4 cover, and replacement window prices in Cardiff gives the published price bands.

Frequently asked questions

Will new windows definitely improve my EPC?

In almost all cases yes, especially if you are replacing single glazing or old double glazing. The new units have a much lower U-value, which the EPC model rewards. The size of the gain depends on your starting glazing and how much window area the home has.

How many EPC points will I gain?

There is no fixed figure, but replacing single glazing often adds several points and can lift a home by a band, while replacing 1990s double glazing usually adds fewer. On a home near a band boundary, new windows can be the change that tips it over. We give a realistic estimate at survey.

What U-value should new windows have?

Part L 2022 requires replacement windows to meet 1.4 W/m2K or a WER of band B or better. The A-rated units we fit come in around 1.2 W/m2K, comfortably inside the limit. Lower is better for both your EPC and your heating bills.

What is the difference between WER A and A+?

Both are strong energy ratings on the A to G window scale, and A+ is a step above A. For a good EPC result, WER A across the house is a sensible baseline, with A+ specified where it earns its place, such as an exposed elevation. We fit A-rated as standard.

Do I need new windows to meet MEES as a landlord?

Most rented homes must reach at least EPC band E to be let lawfully under MEES. New windows are one of the clearer ways to move a poor rating upward, especially where single glazing remains. We can prioritise the rooms that will improve the score most.

Will new windows stop condensation?

They greatly reduce condensation on the glass, because the warmer inner pane no longer gives a cold surface for moisture to form on. You still need to ventilate to manage humidity in the room. New seals also cut the draughts that come with old frames.

Do I get a certificate for new windows?

Yes. Replacement windows are notifiable under Building Regulations, and because we are FENSA registered we self certify the work and your FENSA certificate is issued automatically. Keep it safe, as you will need it when you sell or remortgage.

Will new windows help me let the property to tenants?

If you let in England or Wales, the property must meet the minimum EPC standard (MEES), currently band E, with tighter bands proposed. Replacing failed single or early double glazing with A-rated units is one of the more reliable ways to lift a borderline rating. Bring your current EPC to the survey and we will tell you where the windows can take it.