How the score becomes a letter
The underlying EPC calculation produces a numerical Energy Efficiency Rating, and that number is what actually drives the letter band shown prominently on the certificate. The scale runs from roughly 1, an extremely inefficient building, past 100 for a highly efficient one, with some very high-performing new builds scoring above 100 due to renewable generation offsetting their energy use. The bands are fixed ranges applied consistently to every domestic EPC in England, Wales and Northern Ireland, which is what allows a buyer to compare two completely different properties on a like-for-like basis using the letter alone.
- Band A: 92–100+ (most efficient)
- Band B: 81–91
- Band C: 69–80
- Band D: 55–68 (typical for existing stock)
- Band E: 39–54
- Band F: 21–38
- Band G: 1–20 (least efficient)
| Band | Score range | What it typically means |
|---|---|---|
| A | 92–100+ | New build or extensively retrofitted with renewables |
| B | 81–91 | Well-insulated, modern heating, good glazing |
| C | 69–80 | Reasonably efficient; the informal target for MEES reform |
| D | 55–68 | Average for existing UK housing stock |
| E | 39–54 | Current minimum legal standard for most lettings |
| F | 21–38 | Below the letting minimum; usually needs remedial work |
| G | 1–20 | Least efficient; typically older, un-retrofitted properties |
What actually moves the score
The calculation weighs several factors together rather than any single feature dominating on its own. Wall insulation and construction type carry significant weight because heat loss through walls is usually the largest single loss route in an older property. Heating system efficiency and controls matter enormously — a modern condensing boiler with thermostatic radiator valves and a programmable thermostat scores far better than an old back boiler with no zoning. Glazing, loft insulation, hot water cylinder insulation and low-energy lighting all contribute incrementally. It's the combination that produces the band, which is why two seemingly similar houses on the same street can land in different bands depending on what work has actually been done and, just as importantly, what evidence of that work is available to the assessor.
- Wall type and insulation (solid wall vs cavity, insulated vs not)
- Loft insulation depth
- Heating system type, age, efficiency and controls
- Glazing type (single, double or secondary)
- Hot water cylinder insulation, where present
- Low-energy lighting throughout the property
