A lot is said about the airtightness of the building envelope, much less about that of ventilation ductwork. Yet a ventilation system with leaking ducts does not deliver air where it should: airflow at the vents drops, the fan works harder, energy use rises and indoor air quality suffers. Under RE2020, ductwork airtightness is one of the points checked at handover.
What we measure
Airtightness test of the air handling unit ductwork in a school complex in the Bas-Rhin: the test device is connected to the sealed network.
The test consists of sealing the vents and ends of a section of ductwork, then pressurising it with a dedicated test device. We record the air flow escaping through leaks, relative to the duct surface tested, and compare it with the limit values of airtightness classes A, B, C or D. The higher the letter, the tighter the ductwork must be: a class B network must leak about three times less than a class A network, and a class C network about nine times less.
The target class is the one used in the thermal study. If the study relies on a high-performance class, the handover test proves that the installed ductwork actually achieves it.
Class A: a visual check may be enough before handover
For ductwork targeting class A, an intermediate test is not necessarily needed. A visual inspection of the network and the use of gasketed components (couplings, bends and branches fitted with seals) are generally enough to secure the final test result.
Classes B and C: an intermediate test is strongly recommended
Result at the end of the test: 5.25 l/s of measured leakage against 9.87 l/s allowed, the ductwork meets the target class.
In class B or C, the maximum permitted leakage rates are very low. A single badly fitted joint, a leaking branch or a poorly tightened flexible coupling is enough to tip the result. And once the suspended ceilings and boxing are closed, the ductwork is no longer accessible.
We therefore recommend an intermediate test, with the ductwork installed but still visible. It makes it easy to locate and fix leaks before the handover test.
Examples from our projects
Ventilation ductwork awaiting testing on the Betschdorf school complex site.
- School and after-school complex (Bas-Rhin): air handling unit network with nearly 330 m² of ducts, class A achieved on supply and class B on extract.
- Higher education building (Strasbourg): six supply and extract networks, nearly 1,500 m² of ducts in total, all measured at class B.
Single-family houses and apartment buildings
The sampling rules and the procedure to follow differ depending on whether it is a house or an apartment building. We will cover this in a future article: what to plan for to pass the RE2020 ventilation checks.
Our support
Exp'Air 67 holds Qualibat 8721 for ductwork airtightness testing. We carry out intermediate and handover tests throughout the Grand Est, in housing and commercial buildings, and can combine ductwork testing with the building envelope airtightness test in the same visit.
Read also: The 5 air leaks that make an RE2020 airtightness test fail