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Blower doors for energy-efficient houses

Published 2023-03-13

Blower doors for energy-efficient houses

With powerful fans in door panels – so-called Blower Doors – Olle Syrén of AEM Byggkonsult checks the airtightness of residential and commercial buildings. Firstly, to confirm developers’ energy calculations and secondly, to detect any air leakage.
– “We see a continued increase in demand for density measurements,” says Olle.

Energy-efficient buildings have long been on the agenda. That is, houses that, thanks to smart design, require minimal energy and therefore have low running costs. Airtightness is an important parameter to consider in order to avoid unnecessary energy consumption. When it is cold and windy outside, a building with poor airtightness lets in large amounts of extra air that needs to be heated. Air leakage and internal overpressure also increase the risk of moisture damage to the building envelope.

This is where Olle Syrén comes in. Olle previously worked as a carpenter, supervisor and project manager on construction sites before he was attracted to AEM Byggkonsult to do construction inspections and density measurements.

– Density measurements started as a ‘fun thing’. We saw a clear need for such measurements. Not least for housing companies that needed to carry out density measurements to verify their own energy calculations in connection with new buildings,” says Olle.

Measures of house tightness
In addition to confirming the energy declarations, these measurements also show that new constructions comply with the Planning and Building Act and are in line with the building law. This, in turn, means that the building authority can issue a final decision, after which buildings are considered completed and can be put into use.

Olle Syrén uses Blower Door

We saw a clear need for density measurements!

Olle Syrén uses three Blower Doors for different tasks.

Olle Syrén

AEM Byggkonsult

How does a Blower Door tightness measurement work? Well, in short, it’s like this: A large fan is installed in a front door using a frame and textile panel that fits tightly around the door frame.

All interior doors should be open while other exterior doors and windows should be closed and fans and ventilation systems should be turned off. First, a certain overpressure (e.g. 50 Pa) is created in the building. The airflow is then reversed to generate a corresponding negative pressure. The average of the airflows required to create these pressures provides a measure of the density of the building.

“Simple and easy”
Olle Syrén talks about the three Blower Doors he uses for different missions.

– The Retrotec 300 fits in an ordinary car. It is simple and straightforward. Ideal for pressure testing in small spaces in apartments and small houses. Then I have a Retrotec 5000. It is the Blower Door that I use the most. Especially in many villas. It is very versatile and can handle small jobs as well as quite large measurements. Our latest purchase is the Retrotec 6310 powerhouse. It has triple fans and I use it mainly for measurements in industrial halls because in these cases it involves moving very large volumes of air.

It is the variety of challenges that makes the job exciting and fun, says Olle Syrén. Mostly Olle test prints newly built houses, but recently he has also been commissioned for industrial properties. One example is the construction company Ylab’s 90 000 square meter transshipment center in Stigamo outside Jönköping.

The Blower Door panel is easily installed in the front door opening.

Advocating early measurements
A measurement usually takes 5-10 minutes. The measurement in this large warehouse took almost an hour. Even with three large fans running at full speed, it takes quite some time to create the right pressure in such large spaces. And in order to get the safest possible test, it sometimes takes some manual effort to control fans and get the pressure you want. All this takes time, of course.

It is increasingly common for construction companies to order density measurements during construction, which Olle also advocates.

– This is when you have the best chance of addressing any air leaks. When everything is painted and finished, you have to demolish walls to fix the defects.

What common errors do you find during airtightness measurements?
– I sometimes find that electricians, plumbers and other tradesmen have been negligent in sealing jobs. In some cases I have observed concrete slabs with leaking sills and poorly operated windows, to give a few examples.

What kind of measurements do you do most?
– The majority of the jobs involve measurements of completed building envelopes. But from time to time, other assignments come up as well. For example, I once assisted in an investigation into the smell of cigarettes between two apartments in an apartment building. Using a blower door, I discovered a leak through the insulation in the foundation of the house.

Is there anything in particular that makes the job challenging?
– No two jobs are the same. There is always some special detail to consider in order to get a good measurement. During the actual driving, you need to make sure that the measurement is done as it should be. In many cases, you need to have door guards so that people do not enter the spaces to be measured. To go to the toilet or “take a breath of fresh air” (laughter). ■

Olle Syrén med Blower Door + dator


Activities: The company is based in Huskvarna and currently consists of four consultants who take on assignments in southern and central Sweden. They are hired as building control officers, help with construction and project management, and carry out inspections, pressure tests, thermography and fire protection documentation.

Measurement solution: Three different sizes of Retrotec’s Blower Doors, which are mobile door fans used to measure the airtightness of buildings to detect possible air leaks.

Contact persons

Thomas Ottosson


Mats Landin

Area of responsibility: Construction, Indoor climate, HVAC
031-704 10 85
031-704 10 70

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