A blower door is a diagnostic device that comprises a variable-speed fan that is mounted in a flexible airtight covering. This covering is designed to fit snugly in a doorway of a building.

A blower door device is designed to provide a measurement of airflow in a building using hoses and a manometer. The device includes associated software, control mechanisms, and a pressure gauge to measure the difference in air pressure inside and outside a building through a process of pressurization and depressurization.

Blower door testing is a process carried out to determine the air infiltration rate of a building. A blower door device to come up with an airtightness reading which involves the use of a pressure gauge to calculate the amount of air that is coming in through any unsealed cracks and openings. The results of the test will indicate whether it is necessary to spend time and money on sealing these leaks.

Blower door tests are usually used as part of the code of compliance testing in the construction of new homes. These tests are also a central part of building energy audits.

A blower test on its own will not make your home more energy-efficient. However, the results of the test will give you a good indication as to the action you can take to improve energy efficiency.

A structure with a low degree of airtightness will need more energy to both heat and cool. During the hot summer months in Florida, your air conditioning system will have to work overtime to compensate for the cool air that is constantly escaping through exfiltration and the warm air that is entering via infiltration. The same process applies to the energy consumed by your heating system in the winter, except this time, it is the warm air escaping and the cool entering.

Blower door tests are performed in Florida and across the country by contractors who have certification from one of the two different blower door test certifying authorities.

Before you call in a contractor to inspect your home and carry out these diagnostics, it is important to make sure they are certified as HERS rated by RESNET or by the Building Performance Institute (BPI).

If a blower door test reveals that your building has a high rate of air leakage, the next course of action is to locate some of the places that you suspect airtightness is being lost. During the test, you can walk around checking the gaps around windows, doors, and other openings with your finger for any noticeable leakages.

Generally speaking, if you invest time and money in attacking airflow leakage points with sealant or filler, you can usually achieve a 20% to 30% reduction in the readings given by a blower door test. This percentage will come down markedly if your house already has a low level (25-30 CMF50) of air leakage.

Remember that airtightness is only desirable if you have adequate means of ventilating a building.

One of the key benefits of improving a building’s airtightness relates to air quality. Reducing airflow into a structure can mean a significant reduction in the numbers of air-borne pollutants, allergens, and microbes.

A greater degree of infiltration can also result in the accumulation of moisture inside the building envelope as airflow allows the entry of water molecules from rain, snow, and water vapor.

The time a blower door test takes depends on the size of the home. Generally speaking, it shouldn’t take longer than 30 minutes or so to complete a blower door test from start to finish. If combined with a whole home audit, the entire process should take approximately 1 - 2 hours.

As of 1 July 2017, Florida law (Section 402.4.1.2, Florida Building Code, 5th Edition 2014 Energy Conservation) stipulates that all new residential constructions must pass a blower door test to ensure compliance with energy code.

Specific requirements are that each new home must have 7 ACH50 or less to pass a blower door test. Existing buildings are not subject to this law but reducing a building’s ACH50 reading is recommended to increase energy efficiency and cut down on energy costs.

Infiltration is the uncontrolled inward leakage of outdoor air that enters a building through cracks, gaps, and other unintentional breaks in the structure.

Exfiltration is the opposite—it describes the uncontrolled outward leakage of indoor air from a building through these cracks and openings.

The most common time to perform a blower door test is at the final stages of building construction when all wall finishes, fixtures, doors/windows, and appliances have been installed.

Blower door tests are also commonly carried out to test the airtightness of older buildings. Over time, seals can wear out, and cracks can open up in the structure envelope, which allows an increase in infiltration and exfiltration. If you begin to feel drafts or notice any unexplained increases in your energy bill, you should consider the option of investing in a professional blower door test.

The results of a blower door test will be delivered in the form of two readings: CFM50 (leakage rate measured in cubic feet per minute at a 50 Pa) and ACH50 (air changes per hour at 50 Pa).

The CFM50 reading is taken from the manometer on the conclusion of the test. The ACH50 is then calculated by multiplying the CMF50 reading by 60 (minutes per hour) by the volume of the building (including the basement) in cubic feet and then dividing the number by the building’s volume.