The "flue gas test" has a precise technical name, it's UNI 10389-1, not a standalone legal duty.
UNI 10389-1:2019 is the Italian technical standard that describes how to measure, on site, the combustion efficiency of a heat generator — what everyone calls the "flue gas test". It doesn't set any deadline: it says which parameters to measure (temperature, O2 or CO2, CO and, for liquid fuel, the smoke index) and with what method. It becomes a mandatory step when DPR 74/2013 invokes it for the energy-efficiency inspection, with an interval that depends on power and fuel — not on the technical standard itself. Here is what it actually measures, how the test works, and how it compares with its foreign equivalents.
What UNI 10389-1 covers, in brief
UNI 10389-1:2019 — "Field measurements — Heat generators — Part 1: Appliances fuelled by liquid and/or gaseous fuel" — is the Italian technical standard that describes how to measure, on site, the combustion efficiency of a heat generator: what's commonly called the "flue gas test" or "combustion analysis". It applies to generators fuelled by gas and/or liquid fuel, for space heating and/or domestic hot water; heat generators fuelled by solid fuel and units built into an industrial process cycle fall outside its scope. A UNI 10389-2 also exists, for other generator types, which this guide doesn't cover.
It's a voluntary technical standard, not a law: no one is required to follow it as such. It becomes a mandatory step where a legal text invokes it, and in Italy that happens through DPR 74/2013, which in article 8 requires combustion efficiency to be measured "in accordance with the UNI technical standards in force". That's the exact point where the technical standard stops being just a reference for professionals and becomes the method used, in practice, to carry out the energy-efficiency inspection required by law.
UNI 10389-1 doesn't set any deadline, though: it says how to measure, not how often. The interval for the energy-efficiency inspection — which depends on the generator's power and fuel — is set by DPR 74/2013, not by this technical standard. For the intervals, and for the difference between routine maintenance and the energy-efficiency inspection, see the guide dedicated to boiler maintenance.
What the "flue gas test" actually measures
The standard defines four parameters, not all required for every type of generator: the first three are used to calculate combustion efficiency, the fourth only applies to liquid-fuelled units.
| Parameter | What it indicates | When it's measured |
|---|---|---|
| Flue gas and combustion air temperature | Together with the oxygen reading, this gives the flue heat loss | Always |
| Oxygen (O2) or carbon dioxide (CO2) | Shows how much excess air enters the combustion | Always |
| Carbon monoxide (CO) | Flags incomplete combustion — a safety issue before it's an efficiency one | Always |
| Smoke index (Bacharach scale) | Unburnt particulate in the flue gas: high values foul the heat exchanger faster | Liquid fuel only |
The analyser's software calculates combustion efficiency from the first three values. The instrument must comply with the UNI CEI EN 50379-1 standard.
How the test actually works
The technician inserts the analyser's probe at the flue gas sampling point and waits for the generator to reach steady-state conditions: the standard requires the flue gas temperature to stay stable within 2 °C before a reading counts as valid. It's a step that's often underrated: a reading taken cold, or during a transient, isn't reliable.
For each parameter the standard requires at least three measurements, at intervals of at least 60 seconds: in the 2019 edition the test, overall, takes around two minutes — shorter than the previous edition. For liquid-fuelled generators, a smoke index reading is added, typically taken with a dedicated manual or electronic pump. The instrument used must comply with UNI CEI EN 50379-1.
The test report records the measured values and the calculated combustion efficiency, with the analyser's printout attached, in paper or electronic form. When the test is part of the energy-efficiency inspection required by DPR 74/2013, this data feeds into the energy-efficiency inspection report (RCEE), using the template set by the DM 10 febbraio 2014, which the technician attaches to the heating system logbook.
What the technician does during the flue gas test
The details depend on the instrument and the generator, but the sequence of a flue gas test under UNI 10389-1 is almost always this.
- Checks the draught and the flue gas sampling point before inserting the analyser's probe
- Waits for the generator to reach steady-state conditions: flue gas temperature stable within 2 °C
- Takes at least three readings, at intervals of at least 60 seconds, of flue temperature, O2 or CO2 and carbon monoxide
- For liquid-fuelled generators, adds a smoke index reading on the Bacharach scale
- The analyser's software calculates combustion efficiency from the measured values
- Attaches the analyser's printout to the test report, and — if it's an energy-efficiency inspection — to the RCEE
"Flue gas test" doesn't set its own legal deadline
UNI 10389-1 says how to measure, not when: the technical standard doesn't contain any interval. It's a common mistake to think the technical standard alone imposes a deadline; when one exists, it's set by the legal text that invokes it — in Italy, DPR 74/2013, with an interval tied to the generator's power and fuel. A combustion analysis carried out outside a legally required inspection still follows the standard's method, but it has no mandatory interval of its own.
What a good flue gas test result doesn't tell you
A pass result means combustion, at that moment, falls within the measured parameters: it doesn't certify the safety of the whole system, it doesn't replace the generator's routine maintenance — which follows the manufacturer's manual, not this standard — and it isn't the same thing as commissioning the heating system. These are separate checks, each with a different object.
This guide is informational material: it does not replace the standards cited, the manufacturer's manual or the judgement of a qualified technician. ToriSet organises deadlines and documents; it does not certify compliance.
The same deadlines, without the spreadsheet to recalculate.
Anyone who reaches the end of a guide like this one usually keeps the dates on a spreadsheet, on a tag, or from memory. It works as long as the assets are few and there is one person keeping track. Here is what changes with a logbook.
A spreadsheet with one date per row, on a single computer
A shared logbook: whoever opens the record sees what's due and who did the last job
You recalculate the next deadline yourself, if you remember
ToriSet calculates it from the last job: by months, by hours of use, or whichever comes first
The reminder is a sticky note or a diary
An email 30, 14, 7 and 1 day before, to you and to whoever has to act
Reports and invoices in a folder, to go looking for when needed
Attached to the job, on the product's record
What changes from one country to the next.
UNI 10389-1 is an Italian technical standard: it describes how combustion efficiency is measured, not whether and when to do it — that's decided by the law that invokes it, where one exists. Outside Italy's borders, every country has its own technical reference and its own legal text, often distinct from each other. Below are the foreign equivalents of the flue gas measurement; the source that counts remains the one cited, together with the generator's manual.
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Italy
References
UNI 10389-1:2019
The technical standard describing how to measure, on site, the combustion efficiency of gas and/or liquid-fuelled generators: flue gas temperature, O2/CO2, CO and, for liquid fuel, smoke index.
DPR 74/2013, art. 8
Invokes the UNI technical standards in force for measuring combustion efficiency: the point where UNI 10389-1 enters the mandatory energy-efficiency inspection.
DM 10 febbraio 2014
Sets the template for the energy-efficiency inspection report (RCEE), the document that the values measured under UNI 10389-1 feed into.
Intervals
Energy-efficiency inspection (includes the flue gas test)
every 4 years for gas, every 2 for oil and biomass, halved above 100 kW
certified technician
NoteUNI 10389-1 sets the measurement method, not the interval: the interval for the energy-efficiency inspection is set by DPR 74/2013. For the full picture of deadlines, see the guide on boiler maintenance.
France
References
Décret n° 2009-649 du 9 juin 2009
Requires annual maintenance (entretien annuel) for boilers between 4 and 400 kW, carbon monoxide measurement included.
Arrêté du 15 septembre 2009
Sets the technical detail of the entretien annuel: measuring the CO content in ambient air and near the appliance, with an anomaly band between 10 and 50 ppm (further investigations) and a grave-and-immediate-danger threshold at 50 ppm, which requires the boiler to be shut down.
Intervals
Entretien annuel with CO measurement
once per calendar year
qualified professional
NoteIn France, CO measurement is built into the mandatory annual maintenance, not a separate inspection like in Italy: the attestation d'entretien already includes it, with its own anomaly and danger bands.
Germany
References
1. BImSchV
The ordinance on small and medium combustion plants: sets the periodic flue gas measurement (Abgasmessung) — oxygen, carbon monoxide, temperature — used to calculate the flue loss (Abgasverlust).
Intervals
Abgasmessung (flue gas measurement)
every 2, 3 or 5 years, depending on the installation's age and control type
district chimney sweep (Schornsteinfeger)
NoteIn Germany, flue gas measurement doesn't follow a public technical standard comparable to UNI 10389-1: the method is set by the 1. BImSchV itself, and it's the district chimney sweep — not a freely chosen technician as in Italy — who has sole authority to carry it out.
Switzerland
References
LRV / OPair
The federal ordinance on air pollution control: sets which systems are subject to the emissions check (Feuerungskontrolle) and which parameters to measure, typically nitrogen oxides and carbon monoxide.
Intervals
Feuerungskontrolle (emissions check)
every 2 years for oil, every 4 years for gas (up to 1 MW)
cantonal or communal combustion inspector
NoteEnforcement stays cantonal: check what your canton applies and who's in charge of carrying out the Feuerungskontrolle in your area.
Austria
References
Wiener Heizungs- und Klimaanlagengesetz 2015 (WHLKG 2015)
Vienna's law on operating heating systems: sets, among other things, the flue gas measurement (Abgasmessung) based on the generator's output.
Wiener Kehrverordnung 2016 (WKehrV 2016)
Vienna's regulation that assigns the flue gas measurement and hearth inspection to the Rauchfangkehrer.
Intervals
Abgasmessung (flue gas measurement, Vienna example)
every 4 years below 26 kW, every 2 years between 26 and 50 kW, every year above 50 kW
Rauchfangkehrer (chimney sweep)
NoteIn Austria this falls under the nine Länder, each with its own heating-system law: the references above are Vienna's, taken as an example, and should be checked for your own Land.
What we get asked most.
What is UNI 10389-1?
It's the Italian technical standard that describes how to measure, on site, the combustion efficiency of heat generators fuelled by gas and/or liquid fuel — the edition in force is UNI 10389-1:2019. It isn't a law: it becomes the reference method where a legal standard, like DPR 74/2013, invokes it.
How does the boiler flue gas test work?
The technician inserts a combustion analyser's probe at the flue gas sampling point, waits for the generator to reach stable steady-state conditions, and takes at least three readings, at intervals of at least 60 seconds, of flue gas temperature, oxygen or carbon dioxide, and carbon monoxide; for liquid-fuelled generators a smoke index reading is added.
What does the boiler combustion analysis measure under the standard?
Flue gas and combustion air temperature, oxygen (O2) or carbon dioxide (CO2) content, carbon monoxide (CO) and, only for liquid-fuelled generators, the smoke index on the Bacharach scale. Combustion efficiency is calculated from the first three values.
What is combustion efficiency and how is it calculated?
It's the percentage of fuel energy the generator actually transfers to the system water, net of the flue loss — the energy that escapes with the hot flue gas. It's derived from flue gas temperature, combustion air temperature and oxygen content measured under UNI 10389-1, with the calculation the instrument applies automatically.
Is the flue gas test always a legal requirement?
No: UNI 10389-1 is a voluntary technical standard. It becomes a mandatory step when it's part of the energy-efficiency inspection required by DPR 74/2013, with an interval tied to the generator's power and fuel — not set by the technical standard itself. The intervals are explained in the guide dedicated to boiler maintenance.
Does ToriSet keep track of the flue gas test and the energy-efficiency inspection?
ToriSet helps you keep to the deadlines set by the applicable rules: you record each generator with its power and fuel, and the digital log of work keeps the attached inspection reports together with the right unit. Taking the measurement and filling in the report remain the responsibility of the certified technician.
Combustion efficiency has a method. Deadlines have a date.
Record every generator with its power and fuel: flue gas test reports stay attached to the right unit, and reminders arrive before the next deadline.
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