What the 2026 edition changes
What changes for a replacement boiler
The 2026 edition keeps the same efficiency minimums a boiler has to reach. What it adds is how the system around that boiler gets worked out and controlled.
- The new boiler has to be sized from a heat loss calculation for the property.
- A gas combi has to be able to turn its output down to suit a typical mid-season heat demand.
- Radiators in the room with the thermostat need their own manual control, usually a thermostatic radiator valve.
None of this touches where a flue can terminate. Flue position is governed separately and does not change with this edition.
When the new rules start
The 2026 edition takes effect on 24 March 2027. Work that is notified to building control before that date, and started before 24 March 2028, stays under the rules that apply now. If your job falls in that window, it is the notification date and the start date that decide which rules your installer is working to. Which Edition of Approved Document L Applies to My Job walks through those dates against a specific job.
Where this shows up in a quote
For a job that falls under the 2026 edition, the quote should show a heat loss calculation behind the boiler size, name the mid-season modulation the combi offers, and list a manual control on the radiators in the thermostat's room. If a quote covers a job close to the 24 March 2027 cut-off and is silent on which set of rules it follows, ask your installer directly. 2026 Edition of Approved Document L Published and Circular 04/2026: Amendments to Approved Documents L and F Published record when these changes were issued.
Today's rules and the 2026 rules, side by side
This lines up what a replacement gas or oil boiler has to meet under the rules working now against what the 2026 edition adds, so you can see which lines in your quote are affected and which aren't.
| What's required | Current rules | 2026 rules |
|---|---|---|
| Boiler efficiency minimum | Must meet the current minimum efficiency | Same minimum carries over unchanged |
| Combi additional measures | A combi must come with the required extra measures | Same measures still required |
| Sizing the boilerAsk your installer to show the heat loss figures behind the size they've quoted | Sized to the property, often on the installer's own working | Sized from a heat loss calculation |
| Combi turn-downLets the boiler run closer to what the house needs once the coldest weeks have passed | No requirement to turn down output for milder weather | Must be able to turn down to a lower, mid-season load |
| Radiator controlsCheck which room your thermostat sits in and whether that radiator has a manual control | Thermostatic radiator valves required on the relevant radiators | Manual controls required on the radiator in the room holding the room thermostat |
This covers what changes for a like-for-like boiler replacement. It doesn't include heat pumps or new-build work, and your installer can confirm which edition a particular quote is working to.
Why Approved Document L now has a different title
Approved Document L Volume 1 carried the title 'Conservation of fuel and power' for years. In the 2026 edition, the same document is titled 'Energy and greenhouse gas emissions'. The ground it covers hasn't moved: insulation, heating systems, boiler efficiency are all still in there. Only the name on the cover has changed.
Why a quote might carry either name
An installer's paperwork that refers to 'Conservation of fuel and power' hasn't necessarily got anything wrong. Jobs that were notified or started before the 2026 rules take effect continue to be governed by the earlier edition, and that edition carried the old title throughout its life. A quote using the old name simply hasn't told you which edition it's working to, because that was the only name in use until the title changed.
A quote that uses the new name, 'Energy and greenhouse gas emissions', tells you the installer is working to the 2026 edition. One that uses the old name could mean either: an older job correctly following the earlier edition, or a quote that hasn't caught up with the new title. The name on its own doesn't settle it.
What to check if the edition matters to your job
If you need to know which edition applies, ask the installer to state the edition directly. You can also check which edition of Approved Document L governs your job against the dates for when your work was notified and started. The title change itself is set out in the record of the Volume 1 title change, alongside the wider publication of the 2026 edition.