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Blower Door Test detects energy leaks
Blower Door Test detects energy leaks
Video: Blower Door Test detects energy leaks
Video: 7. Energy Leaks Energy Assessment - Blower Door Test 2023, February

Is your house not completely sealed? If you are not sure whether you are wasting valuable energy, a blower door test may bring certainty. With this method, also called differential pressure measuring method, you can measure the airtightness of a building and find leaks in the building envelope.

Anyone who builds a house wants to feel comfortable in the new domicile and reduce the loss of energy as much as possible. Of course, the new building should also meet the requirements of the Energy Saving Ordinance (EnEV). The blower door test can make an important contribution to this along with other measures. So that no heat is lost through joints and crevices, the building must be given an airtight shell.

The blower door test procedure is technically mature and has been practiced since the first thermal insulation regulation came into force in 1995. As soon as the house is completely closed, you can check its tightness during the construction phase and detect leaks when they can usually be removed without much effort.

How the Blower Door Test works

And this is how it works: A special fan pushes air in or out of the building. Different sized orifice plates for the conveyed volume flow are used to adapt the conveyed air flow to the building tightness. The size of the volume flow is displayed by calibration. The fan is set so that there is a pressure difference of 50 Pa (Pascal) to the ambient pressure. This pressure difference also arises naturally in the house, for example when the wind is blowing outside with wind force 5. The fan is surrounded by an adjustable metal frame and an airtight tarpaulin and is inserted in a door or window opening. Rubber seals are airtight on the door or window frame.


The blower door test has been tried and tested for years, but according to experienced construction experts, it is still used far too rarely for quality testing on new buildings.

Photo: Association of Private Builders (VPB)

The door or window in which the measuring device is used cannot be measured. So if you want to measure the front door, you cannot install the blower door device there, but have to look for an alternative - for example a balcony door.

The measuring instruments determine the pressure differences that the fan generates and the air volumes that the fan transports. The fan speed is controlled so that a certain pressure builds up between the outside and the inside. In doing so, he has to transport as much air to the outside as can penetrate the building through the existing leakage points. The measured air flow is divided by the volume of the building. This value, the air exchange rate n50, can now be compared with other buildings and standards.

The blower door test consists of three phases

  1. In the first phase, a constant negative pressure of 50 Pa or slightly higher is created and maintained. During this phase, the building envelope surface is searched for leaks, i.e. leaks, at which air flows in undesirably. Larger leaks can already be felt by hand, for smaller ones you use smoke machines or air speedometers. The most accurate measurements are possible using an infrared camera.
  2. In the second phase, a negative pressure is built up, starting with small pressures (10 to 30 Pa) and gradually increasing to the final pressure of 60 to 100 Pa. At each step, the respective air volume flow is measured and logged depending on the building pressure.
  3. In the third phase, an overpressure is generated and the measurement is repeated analogously to the underpressure measurement. A blower door examination on a single family home takes about three hours in total. Once the measurements have been completed and the air exchange rate has been maintained, the homeowner receives a certificate of the quality of the measured building envelope.

It is best to rely on independent quality control

In the end, the builder is responsible for ensuring that his house meets the legally required low-energy standard. Problems can arise when craftsmen work too carelessly or are not adequately trained - for example, if windows or doors are not connected to the masonry in an airtight manner or the transitions from the wall to the roof are leaky.

Although turnkey providers are now also offering the blower door test as part of their service package, private builders should rather hire independent experts for this and have an independent, final quality control with blower door test and thermography guaranteed in writing in the contract. Blower door test is not the same as blower door test: it depends on when, how, by whom and with which additional measures it is carried out. In addition, each client should have the results of the tests on their property explained and handed over to them. That is part of serious providers.

Combinations of blower door test and thermography have proven their worth. These procedures have now become the technical standard and, if there is a dispute, are also recognized in processes. However, the methods are not yet very widespread: only about half of all new buildings are currently undergoing a blower door test. And not even a fifth of all houses are checked for energy leaks using thermography.

The cost of a blower door test

The cost of the blower door test basically depends on the effort. You start with a family home at around 300 euros. However, this basic service usually only includes the location of leaks. It costs a little more if an energy consultant takes the test - around 500 euros. For this you get a precise measurement report, photo documentation and a certificate. If an energy consultant conducts this Kfw 70 blower door test, you may be able to receive state funding. As part of the Kfw program 431 (construction support by an energy consultant), up to 50 percent of the costs - up to a maximum of 2, 000 euros - are borne.

How is the procedure regulated?

The German DIN 4108, Part 7 requires the "installation of an air-impermeable layer over the entire surface". The differential pressure process is standardized in ISO 9972: 1996 and the EN 13829 thermal behavior of buildings based on it - determination of the air permeability of buildings. Differential pressure method, German adoption of DIN EN 13829: 2009-11.

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