Ductwork airtightness

What is ductwork airtightness?

Ductwork airtightness can be defined as the resistance to inward or outward air leakage through the ductwork shell.

What is the energy impact of building and ductwork airtightness?

The implementation of the EPBD recast puts increasing pressure to achieve better building and ductwork airtightness since for most European climates and countries, good airtightness levels are necessary to achieve nearly zero-energy buildings. This has been shown in a number of studies with energy impacts of the order of 10 kWh per m2 of floor area per year for the heating needs in a moderately cold region (2 500 degree-days) and 0 to 5 kWh/m2/year for the ducts plus the additional fan energy use [1]. For more information see also the ASIEPI project technical report on building and ductwork airtightness as well as REHVA journals’ special issue on airtightness [2].

[1] G. Guyot, F. R. Carrié and P. Schild, “Project ASIEPI – Stimulation of good building and ductwork airtightness through EPBD,” 2010.

[2] R. Coxon, “Research into the effect of improving airtightness in a typical UK dwelling,” The REHVA European HVAC Journal-Special issue on airtightness, vol. 50, no. 1, pp. 24-27, 2013.

How is the ductwork airtightness quantified?

Duct airtightness classes A to D are defined in European Standard EN 12237 for circular ducts and EN 1507 for rectangular ducts. Class A is the leakiest class. A parallel standard to EN12237, EN 1507 and EN 1751 based on the same leakage classification is EN 15727 which applies to technical ductwork products and specifies the leakage requirements for technical ductwork products. The leakage test method for system commissioning is described in EN 12599. Airtightness classes for air handling units (L1 to L3) are defined in EN 1886. System standards, in particular EN 13779, give further recommendations for airtightness class selection for different purposes. [1]

[1]G. Guyot, F. R. Carrié and P. Schild, “Project ASIEPI – Stimulation of good building and ductwork airtightness through EPBD,” 2010.

Are there databases on building and ductwork airtightness?

France, Belgium (Flemish Region) & the United Kingdom have national databases that gather most of measurements performed by qualified testers in their countries. Other initiatives also exist in Spain, Germany, Czech Republic, Estonia and the US [1], [2].

More information can be found in AIRBASE, the Bibliographic Database of the AIVC (e.g. search on “database”), as well as the Proceedings of AIVC & TightVent Joint conferences and workshops.

[1] V. Leprince, F. R. Carrié and M. Kapsalaki, “Building and ductwork airtightness requirements in Europe – Comparison of 10 European countries” in 38th AIVC Conference “Ventilating healthy low-energy buildings”, Nottingham, UK, 13-14 September 2017, Nottingham, 2017.

[2] V. Leprince, M. Kapsalaki, F. R. Carrié, “VIP 37: Impact of Energy Policies on Building and Ductwork Airtightness” AIVC, 2017.

What are relevant CEN standards related to building & ductwork airtightness?

TightVent Europe has published a list of applicable standards for building and ductwork airtightness. The detailed list can be found here.

Is building and ductwork airtightness testing mandatory?

It depends on the country and context of the measurement. Most EU countries include in their regulations either required or recommended minimum airtightness levels with or without mandatory testing. There are several countries (e.g., United Kingdom, France, Portugal, Denmark, Ireland) where, by regulation, airtightness testing is mandatory for certain building types or in the case of specific programmes [1].

[1] V. Leprince, M. Kapsalaki and R. Carrié, “Right and Tight: What´s new in Ductwork and Building Airtightness?,” BUILD UP energy solutions for better buildings, 2 October 2017.

What sort of certification programmes for ductwork airtightness exist?

Short answer:

Eurovent Certita Certification have a certification programme for rigid and semi-rigid ventilation ductwork systems.

Long answer:

Eurovent Certita Certification have a certification programme for rigid and semi-rigid ventilation ductwork systems divided into the following sub-programmes:

Each sub-programme applies to ductwork systems fitted with integrated sealing solution as described in the Technical Certification Rules ECP-19.

This programme contains amongst other, airtightness and static gauge pressure limit criteria and is based on European standards.

The certification process is to periodically check the resilience of the company quality system by auditing manufacturing sites and the certified performances of a ventilation system by a third-party laboratory measurement.

The certification brings the supplier products, its technical documentation and quality resilience to a reliable level.

The DUCT program does not cover other types of ventilation ductwork elements like flexible ducts, double-wall ductwork or ductwork made of insulation ductboards.

The Swedish type approval for metallic ducts has been a very important driver for the ventilation business. The requirement based vision has driven the ventilation business since the beginning of the 1970’s  to sustainable solutions with demands on airtightness and strength without a demand for sheet steel thickness. This has led to airtight energy efficient  duct work solutions with as little material as possible.

The Swedish Type approval issued by governmental Boverket is only valid in Sweden but has been widely used in other countries as well. There are two Swedish bodies accredited by SWEDAC to issue type approvals, RISE and Kiwa.

Finland has developed their own approval based on the Swedish type approval and is handled by the Finnish Ministry of Environment, and Eurofins Expert Service Oy is authorized by the Finnish Ministry of Environment to issue type Approvals for building products.

What is an airtightness/air leakage testing? What is fan pressurization?

A method of quantifying how much air leaks into or out of an enclosure. EN 13829 gives a standard test method for buildings. Several standards apply to ductwork systems (see also “How is the ductwork airtightness quantified?“).

Building airtightness levels can be measured by using a fan, temporarily installed in the building envelope (a blower door) to pressurize the building. Air flow through the fan creates an internal, uniform, static pressure within the building. The aim of this type of measurement is to relate the pressure differential across the envelope to the air flow rate required to produce it. Generally, the higher the flow rate required to produce a given pressure difference, the less airtight the building [1].

[1] M. Limb, “Technical note AIVC 36- Air Infiltration and Ventilation Glossary,” International Energy Agency energy conservation in buildings and community systems programme, 1992.

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

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.
  • Energy use: Air leakage may inadequately increase the total ventilation airflow rate; or it may not allow sufficient heat recovery (in case of a systems with heat recovery devices, the unit will only recover heat on the airflow passing through it).
  • Building materials: Air leaking out of the envelope may cause condensation damage as its temperature drops below dew point.

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 indoor air quality (in terms of lower air change rates and ventilation efficiency in rooms), comfort, and fire protection. It is often accompanied by other problems, such as inferior commissioning and cleaning. 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 duct airtightness but also with safety and indoor environment. [1]

[1] G. Guyot, F. R. Carrié and P. Schild, “Project ASIEPI – Stimulation of good building and ductwork airtightness through EPBD,” 2010.

Definitions of terms used for tightening products


Adhesive:  Substance that holds one surface to another surface by attachment.

Adhesive membrane: Flexible film (generally made of polyethylene) associated with a nonwoven fabric used to seal joints between the peripheral of a window and a vapour barrier/retarder or a plaster.

Bond: Material used to tie or fasten things together.

Expanding foam: Expanding material (generally polyurethane-based) applied to fill gaps, to fix doors and to insulate connecting joints (especially between window frames and wall).

Fastener: Material used to bind things securely together.

Grommet: Material used to create an airtight seal around circular-section elements such as plumbing pipes, electrical conduits or cables as these pass through the airtight layer.

Joint: Location where several parts of the structure (building or ductwork) meet.

Sealant:  A material that has the properties to join 2 surfaces together to prevent gases, liquids or solids from passing between these surfaces.

Mastic: Putty-like sealant.

Plasters: Fluid or paste-like mixtures made of cement, lime, or gypsum. These products are spread or projected on the surface.

Pre-compressed tapes: (also called pre-compressed foams) Rolls a few centimetres wide whose thickness is reduced when rolled-up and slowly get thicker when installed. They are made of polyurethane or polyester foams impregnated with a synthetic butyl or acrylic resin. The retarded decompression process allows the gaps to be filled while the foam was put without force into them.

Repair tape: Oversized tape roll or flat patch typically used to repair holes in films or holes made on purpose e.g., for blowing insulation.

Tape: An adhesive in the physical form of a tape, i.e., a narrow strip of material.

Vapour barriers or retarders: Membranes or films of large areas originally intended to limit or regulate vapour transfer within vertical walls and roofs. When properly installed and at the right location, they prevent interstitial condensation, in particular in the insulation layer. Their composition can be very diverse, e.g. they can be partly made of polyethylene, polyester, polyane, aluminium, etc. They are usually airtight unless perforated.

[1] Ramachandran, V., Paroli, R., Beaudoin, J., & Delgado, A. (2002). Handbook of thermal analysis of contruction materials. USA: Noyes Publications / William Andrew Publishing.

[2] F. Carrié, R. Jobert and V. Leprince, “Contributed Report 14- Methods and techniques for airtight buildings,” AIVC, 2012

What is TAAC? How can I be involved?

Short answer:

TAAC is the TightVent Airtightness Associations Committee and has the primary goal to bring together national associations and experts on building and ductwork airtightness in order to promote reliable testing and reporting procedures.

Long answer:

TAAC  is the TightVent Airtightness Associations Committee, launched in September 2012 by the TightVent Europe platform, with the primary goal to bring together national associations and experts in order to promote reliable testing/inspection and reporting procedures.

The scope of TAAC includes various aspects such as: building & ductwork airtightness requirements in the countries involved; competent tester schemes in the countries involved; applicable standards and guidelines for testing; inspection of ventilation systems; collection of relevant guidance and training documents; share of knowledge and experience; and information on ongoing research work in the field of building and ductwork airtightness.

At present the participants are from Belgium, Czech Republic, Estonia, France, Germany, Hungary, Ireland, Latvia, Netherlands, Poland, Portugal, Spain, Sweden, Switzerland, UK and the US.

In case you are interested to join this initiative, please write an email to: info@tightvent.eu.


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