EPC vs DEC: what's the difference?
An EPC rates how a building was designed and built; a DEC rates how much energy it actually consumed over the last 12 months.
The two certificates look similar — both use an A to G scale — but they measure fundamentally different things. An Energy Performance Certificate is an asset rating produced from a model of the building's fabric and services under standardised use. A Display Energy Certificate is an operational rating produced from metered consumption data. A public building can hold an EPC B and a DEC E at the same time, and that gap is usually where the savings are.
EPC vs DEC, attribute by attribute
| Attribute | EPC | DEC |
|---|---|---|
| What it measures | Modelled asset performance | Actual metered energy use |
| Basis | SBEM or DSM model, standardised occupancy | 12 months of real meter readings |
| Who needs it | Anyone selling, letting or completing a building | Public authority buildings over 250m² visited by the public |
| Validity | 10 years | 1 year over 1,000m²; 10 years for 250–1,000m² |
| Display requirement | Provided to buyers and tenants | Must be displayed prominently to visitors |
| Affected by occupier behaviour | No | Yes, heavily |
Which one applies to you
Choose EPC when
- /You are selling or letting commercial space
- /You need to evidence MEES lettability
- /A new building is reaching practical completion
Choose DEC when
- /You operate a public building over 250m² that the public visits
- /You want to evidence real operational savings year on year
- /You are reporting estate energy performance to a public body
Most public estates need both: the EPC on transaction and construction events, the DEC annually on display. Read together they show whether a well-designed building is being operated well.
Common questions
+Can a DEC replace an EPC?
No. They are separate statutory instruments — a DEC cannot be used to evidence MEES compliance or a sale, and an EPC does not satisfy the public display duty.
+Why is my DEC rating worse than my EPC rating?
Because the DEC reflects real hours, occupancy and equipment while the EPC assumes standardised use. A large gap usually points to controls, plant scheduling or out-of-hours consumption rather than the building fabric.