The oil smoke test: what it measures and why it matters
The smoke test draws a measured sample of flue gas through filter paper and compares the resulting stain against a standard scale, giving a direct read on how cleanly the burner is combusting fuel.
The oil smoke test: the short technical version
A high smoke number indicates incomplete combustion, meaning unburnt carbon particles are passing through the appliance rather than releasing their full energy. This wastes fuel and gradually deposits soot on the heat exchanger, reducing its efficiency further over time. The test is quick to perform and is combined with a flue gas analyser reading to give a full combustion picture, since the two measurements check different aspects of how the burner is performing.
Practical notes on the oil smoke test
- Smoke number is read against a standard comparison scale
- High smoke numbers indicate incomplete combustion and wasted fuel
- Soot from poor combustion deposits on the heat exchanger over time
- Usually performed alongside a flue gas analyser reading
- A clean result supports confidence in the overall burner setting
Where we deal with this
Relevant registrations
- Gas Safe registered for domestic gas boiler work
- OFTEC registered for oil boiler work
- Worcester Bosch Accredited Installer
Straight answers on the oil smoke test
Our advice: The smoke test is a simple, fast way to confirm an oil burner is converting fuel into heat efficiently rather than into soot.
Include the appliance make and model in your enquiry so the correct technical information can be checked.
Related help pages
- Selling a propertyShould you service the boiler before selling a house
- Oil compliance paperworkOFTEC service paperwork: what a CD/11 style record shows
- Appliance ventilationVentilation checks: why airflow around an appliance matters
- Guarantee supportWhy service records matter for a manufacturer guarantee
- Vitodens fault codeViessmann F2: flow temperature sensor fault on a Vitodens
- Grant rangeGrant Vortex Blue: the higher-specification oil range
Services that cover this
Questions we get asked
- What is considered a good smoke test result?
- Manufacturers specify an acceptable range, and a competent engineer adjusts the burner until the reading falls comfortably within it.
- Does a poor smoke test always mean a fault?
- It usually means the burner setting needs adjusting, though it can also point to a worn nozzle or contaminated fuel.
New Worcester boiler with a 10 year guarantee*
Free no-obligation quotes for installation, servicing & repairs across BA & BS postcodes.