How an EPC works
An Energy Performance Certificate (EPC) gives your home an energy efficiency rating from A (best) to G (worst). GOV.UK says it is valid for 10 years.
It shows how much energy your home uses and its typical energy costs. It also lists steps you could take to make the home more efficient.
You can look up your current EPC for free on GOV.UK using your postcode, or use our free energy check.
Where windows fit in
The assessor looks at how your home is built and heated. That includes the walls, the roof, the heating system, hot water and the type of glazing.
Because of this, the same new windows can make a big difference in one house and a small one in another. A home with single glazing and good loft insulation has more to gain from new windows than a home that already has double glazing.
A window energy rating is not the same as an EPC
Windows can carry their own energy rating, often shown as a letter from A upwards. That rates the window as a product.
Your EPC rates the house. An A-rated window does not make your home A-rated. It is one upgrade that helps the whole picture.
| EPC | Window energy rating | |
|---|---|---|
| What it rates | Your whole home | One window product |
| Scale | A (best) to G (worst) | A letter rating for the window |
| Who gives it | An accredited energy assessor | The window maker, through a rating scheme |
| How long it lasts | Valid for 10 years | Applies to that product |
| Where to find it | GOV.UK Find an energy certificate | Ask your installer for the product rating |
When new windows make the biggest difference
New windows are most likely to help if you have:
- Single glazing anywhere in the house.
- Double glazed units that have misted up between the panes.
- Frames that rattle, stick or let draughts in.
- Old windows that no longer close tightly against their seals.
Replacement windows must meet the rules
Building regulations have applied to replacement glazing in England since 1 April 2002. New windows must meet energy limits set under Part L.
An installer registered with a competent person scheme can self-certify the work. You get a certificate when it is complete. Keep it with your house papers.
Will my EPC change on its own?
No. Your certificate stays the same until a new assessment is done. If you plan to sell or let your home, a new EPC after the work will show the upgrade.
Sources
General facts on this page come from these official sources. Rules can change, so check the latest version before you rely on them.
- GOV.UK: Energy Performance Certificates (EPCs) (opens in a new tab)
- GOV.UK: Find an energy certificate (opens in a new tab)
- Planning Portal (government planning and building regulations service): Doors and windows, building regulations (opens in a new tab)
- GOV.UK: Conservation of fuel and power, Approved Document L (opens in a new tab)
- GOV.UK: Use a competent person scheme (building regulations approval) (opens in a new tab)