What is the impact of duct leakage on comfort, ventilation, indoor air quality and fire security?

Duct leakage is not only detrimental to energy efficiency, but also to indoor air quality (in terms of lower air change rates and ventilation efficiency in rooms), comfort, fire protection, noise, dust accumulation, moisture damage or even contamination issues. 

When the fan compensates for ductwork leakage by generating higher pressure and flow rates, energy losses are induced. When the fan does not (or only partially) compensate for leakage, the hygienic flow rate is not reached at every air terminal device, inducing indoor air quality (IAQ) issues especially in rooms located far away from the fan.

In a pandemic context, one can note that air leakage in extract ducts can also spread contaminants such as viruses to other parts of the building. Leaks located downstream the filter and upstream the fan can lead to polluted air bypassing the filter, leading to poor IAQ issues.

In Scandinavia good ductwork airtightness has largely been promoted together with indoor air quality benefits. Note that the Swedish VVS AMA guideline not only deals with energy issues related to ductwork airtightness but also with safety and indoor environment. [1].

In  [2], other effects than energy losses and IAQ issues are reported, such as changes in noise that tends to increase with increasing duct flows [3]. Leakages can have 3 noise related effects:

  1. Increasing fan flowrate and pressure needed will increase the noise produced by the fan
  2. Leaks can also increase the transmission of fan sound pressure
  3. Leaks can create their own “whistling” noise

It is also believed that leakages can increase dust accumulation in filters [4], heat exchangers and ducts, as there is more flow rate going through.

Moreover, ductwork leakages lead to uncontrolled airflows that may induce depressurization causing backdrafting of combustion equipment or pressurisation causing moisture damage in walls [5]. This unbalance may also weaken contamination protection of sensitive areas (operating theatres, clean rooms, etc.)

Finally, fire-rated ventilation ducts can avoid fire and heat spread between two building compartments, but this can be compromised by ductwork leakage.


[1] Guyot, G., and Carrié, F.R., 2010. Stimulation of good building and ductwork airtightness through EPBD. ASIEPI, 2010.

[2] Leprince V., Hurel N., and Kapsalaki M.,2020. VIP 40 Ductwork airtightness – A review.  AIVC, April 2020

[3] Richieri, F., et al., 2018. Ductwork design flaws and poor airtightness: a case study about a ventilation system reconditioning in a sealed building. Proceedings of the 39th AIVC-7 th TightVent-5 th venticool Conference, 18-19 September, Juan-Les-Pins, France. pp. 442-451.

[4] Dyer, David F., 2011. Case study: Effect of excessive duct leakage in a large pharmaceutical plant. Proceedings of the 32nd AIVC & 1st TightVent Conference, 12- 13 October. Brussels, Belgium. pp. 55-56.

[5] Modera, M., 2005. Fixing duct leaks in commercial buildings. ASHRAE journal, pp. 22- 28.

See also

Is it possible to improve the airtightness of a ductwork after completion?

To improve the air tightness of existing air ducts, a method of sealing the ducts by applying a sealant using a spray atomizer was developed in the USA in the early 2000s and is now (since 2015) being used in Europe. This method [1] can reduce leakage in an installed air duct system by 66-86% and can therefore improve the air tightness after installation.  This can have other positive side effects, such as the impact on energy costs, indoor air quality & comfort or hygienic requirements.


[1] MEZ-AEROSEAL. https://www.mez-technik.de/en/mez-aeroseal.html

Is good building airtightness compatible with good indoor air quality?

Yes, provided that the building is equipped with an appropriate ventilation system (whether natural, mechanical or hybrid). A French study mentioned in the AIVC newsletter n°2 shows that better building airtightness converges with better indoor air quality because the ventilation system operates more efficiently. Building leaks cause uncontrolled airflows and potentially poorly ventilated rooms although the total building air exchange rate may be sufficient [1].

[1] L. Mouradian and X. Boulanger, “QUAD-BBC, Indoor Air Quality and ventilation systems in low energy buildings,” AIVC Newsletter No2, June 2012.

What are the impacts of poor envelope airtightness on ventilation, indoor air quality and building damage?

Air infiltration adds to the quantity of air entering the building but may also distort the intended ventilation air flow pattern to the detriment of overall indoor air quality and comfort. The consequences are inferior performance, excessive energy consumption, and inability to provide adequate heating (or cooling) [1].

Because air infiltration is uncontrolled, poor envelope airtightness may affect:

  • Indoor air quality: Some rooms may be largely under-ventilated while other are over-ventilated as a consequence of distorted air flow patterns. Also the air circulating in the wall may bring inside pollutants from outside and from building product emissions.
  • Energy use: Air leakage may inadequately increase the total ventilation airflow rate; or it may decrease the relative impact of heat recovery (in case of systems with heat recovery devices, the unit will only recover heat on the airflow passing through it).
  • Moisture performance: air leaking through the envelope from a warm, humid environment to a cold environment, may cause condensation damage as it flows along materials with a temperature below its dew point. In cold climates condensation damage may occur in materials at the outside of the thermal insulation when air exfiltrates, while in warm climates damage may occur at the inside of the insulation when air infiltrates.
  • Acoustic performance: airborne sound may propagate through leakages. It is found that sound transmission loss can be degraded by up to 15 dB under field conditions, mainly because of sound leaks.


[1] Liddament M.W., 1996. A Guide to Energy Efficient Ventilation. AIVC, 1996.


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