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What is a Flue Dilution System?

What is a Flue Dilution System?

A Flue Dilution System is typically installed in areas where there are problems installing the flue above roof level. The system helps disperse emissions produced during the combustion process at low levels & complies with the following regulations: 1993 Clean Air Act, British Standard 6644 and Institution of Gas Engineers & Managers.

Flue Dilution System


1992 Clean Air Act

The 1992 Clean Air Act was put in place to consolidate the Clean Air Acts of 1956 & 1968. The Clean Air Act states that if products of combustion are dispersed at low levels then the carbon dioxide content should be less than 1%. A flue dilution system is able to adhere to this regulation through releasing fresh air into the boiler’s discharge flue duct. This dilutes the flue gases reducing the carbon dioxide levels.


A regulatory pressure device or pressure safety switch can be installed on the fan dilution system to prevent operation of the burner when these situations arise:

  • Stalled fan motor
  • Blocked intake causing a blocked fan air supply
  • Interrupted power supply

When the fan is operating correctly, the pressure safety switch will enable the boiler to fire up.



Flue dilution systems are compatible with natural gas or liquid petroleum gas fuel sources. They cannot be used with oil fired boilers due to there being no way to immediately shut off an oil fired boiler in the event of fan failure.