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What do the Part L Building Regulation changes mean to you?

As part of the Government’s roadmap to help the UK move towards its net zero target by 2050, updates to Part L Building Regulations will enforce tighter water heater energy efficiency standards from 15th June 2022.

One key change relates to stricter thermal efficiencies for non-domestic hot water systems. All direct fired water heaters must achieve a minimum heat generator efficiency of 91% (GCV) for natural gas and 92% (GCV) for Liquified Petroleum Gas (LPG). For indirect water heaters, the minimum heat generator seasonal efficiency is set at 91% for both natural gas and LPG.

This effectively, removes the current option to carry out like-for-like non-condensing water heater replacements in the vast majority of non-domestic buildings.

Only in very exceptional circumstances, where condensing water heater replacement is deemed not suitable or practical by the Building Control Body (for example, where there is insufficient space for a replacement flue system), then a water heater with a minimum seasonal efficiency of 80% for Gas or 79% for LPG may be used.

So now is the time to make the most of the opportunity to carry out like-for-like replacements with non-condensing water heaters. This means that, as no major work is involved, they can be replaced quickly with minimal disruption to the daily operation of the building.

There are lots of benefits to condensing water heaters. Condensing water heaters, are energy efficient water heaters so unlike non-condensing varieties can capture and reuse latent heat that is otherwise lost to atmosphere. As a result they are up to 20% more efficient that non-condensing models. Units like the Andrews Water Heaters ECOflo, MAXXflo EVO and SUPAflo EVO are high efficiency water heaters, achieving near maximum efficiencies of up to 98%. NOx emissions are also lower making them the natural sustainable choice in new build premises and building refurbishments.

What options are available after 15th June 2022?

You may choose to switch to a condensing Andrews water heater. This route could be the most straight forward depending on circumstances although there are some considerations. Certain factors such as flueing and condensate arrangements, will need to be assessed on a project by project basis.


The original non-condensing atmospheric water heater will generally be fitted to a conventional open flue. This is not suitable for condensing water heater due to:

  • Acidic content of the condense
  • Positive flue pressure
  • Low flue gas temperatures
  • Requires a minimum 3 ̊fall back to the appliance on horizontal flue sections.

So generally the conventional flue system will need to be replaced or undergo major alterations. One option may be a concentric flue if the location is suitable or a boiler and a cylinder or plate heat exchanger combination could solve the issue.


There will be a need to remove the condense produced by the new water heater. This can be pumped if there is no easy drain access or the acidity can be neutralised for discharge into storm drains via a neutralisation kit.

Water supply

Previous older non-condensing models could operate with a 0.2 bar water pressure. However condensing models need a higher pressure to operate. Optimum performance can be achieved when units are connected using the mains cold water unvented system kit.

Whole plantroom solutions

Andrews Water Heaters is part of Baxi Commercial Solutions so our expert areas sales managers can advise on a number of other solutions including

Our expert Technical Sales Managers offer free site visits to run through some of these considerations and to provide the best bespoke solution to your heating and hot water challenges.

Customer support