UK Building Regulations Part L Uplift: Where are you now?

An update on Part L and the latest requirements across England, Wales and Scotland.

Last year, England Wales and Scotland introduced more stringent energy efficiency requirements in their Building Regulations and Standards.  At the heart of these updates was the enforcement of tighter water heater energy efficiency standards in commercial and industrial water heating applications which has effectively removed the option to carry out like-for-like non-condensing water heater replacements in the vast majority of commercial buildings (exceptions apply).

However, with England, Wales and Scotland all at different junctions on the road to Net Zero, it’s important to keep an eye on these changes to ensure you’re staying ahead of the latest requirements.

A year on…


  • On 15th June 2023, the grace period for the update to Part L of the Building Regulations ended.  The associated compliance requirements are now mandatory.
  • Regulations for hot water systems now impose minimum efficiencies of 91% for natural gas and 92% for LPG. However, where condensing water heater replacement has been deemed not suitable or practical by the Building Control Body, a minimum seasonal efficiency of 80% for gas, or 79% for LPG may be used.


  • From 29th March 2023, the update to Part L of the Building Regulations became mandatory.
  • For projects already past planning stage, or where there was insufficient space for a replacement flue, a 12-month grace period was granted.  This will conclude on 29th March 2024.
  • For indirect water heaters, the minimum heat generator seasonal efficiency is set at 92%.



  • From 1st February 2023, the update to Part L of the Building Regulations became mandatory.  This is applicable to works subject to a building warrant submitted on or after this date or works which do not require a building warrant (i.e., one that is already in place).
  • Regulations imposed for minimum efficiencies of 93%.
  • For projects where a building warrant was granted before 1st February 2023, the previous efficiency of 81.65% applies.


By now, we should all be up to date on the benefits of condensing units. Unlike non-condensing varieties, condensing units can capture and reuse latent heat that is otherwise lost to atmosphere. As a result, they are up to 20% more efficient than non-condensing models. 

Furthermore, in line with the current ErP requirements which state that water heaters must operate under specific NOx (nitrate oxide) thresholds of 56 mg/kWh for a single appliance, condensing water heaters contribute fewer emissions to the environment, making them a more sustainable choice in new build premises and building refurbishments

The good news is that the ACV product offering such as the WaterMaster Evo, HeatMaster Evo AND EVO S all significantly exceed the latest minimum efficiency thresholds required for Part L2 compliance and provide a compliant solution.