What are existing methods to estimate building airtightness? Are there other test methods apart from fan pressurization?
Existing methods to estimate building airtightness include:
- Fan pressurization, multi point test
- Fan pressurization, single point test
- Pulse test
- Tracer gas test
Fan pressurization, multi point ,
From a multi point pressurization test the airflow through the leakages in the building envelope is measured at different building pressures differences. A blower door uses a fan to depressurize or pressurize the building envelope. Both a multi point and a single point test can be carried out with the blower door. From the multipoint test a leakage graph with flow coefficient and leakage exponent can be generated in order to calculate air leakage rates at different building pressure differences (e.g. at 50 Pa, 4 Pa etc.) to determine for example the air change rate of a building. This measurement method is described in ISO 9972:2015.
With a single point test it is possible to get a rough estimation of the airflow at a certain building pressure difference. The fan is adjusted to the target pressure and the air flow is read to determine a value of interest (e.g. the air change rate at 50 Pa). The blower door method is extensively described in the FAQ "What is a blower door?".
1-point measurement using the home's ventilation system 
A method developed in the Netherlands uses the ventilation system to pressurize the building.The instrument consists of a reference vessel fitted with a valve and a differential pressure meter. Before the start of the measurement the valve is open and the ventilation system is off. At the start of the measurement the valve closes. While the ventilation system is switched on and off several times, the pressure difference between the building and the reference vessel is measured. From this pressure difference in combination with the ventilation volume flow, the air permeability is determined. The time required for the 1-point measurement is limited (approximately 10 minutes). The preparations and conditions of the building or building section to be tested are the same as for the determination with a blower door. As mentioned already, for a single point measurement the flow exponent must be chosen.
The Pulse test , 
The pulse test was developed in the UK. The measuring principle of the pulse test (Jens Couckuyt, 2018) is: "The device contains an air tank with a certain capacity, e.g 60 liters. The vessel must be charged by a compressor. During the measurement a known volume of air is sent out for one and a half seconds. This causes a short rise (pulse) in the air pressure. This pressure rise provides airflow through the air leaks. Over time the pressure difference will be stabilized again. The pressure difference, during two seconds before and after the air pressure pulse, is also recorded by the device. The container must be refilled after the test. The measurement result is calculated at a pressure difference of 4 Pa. The pressure range that is achieved is not the same for every test. It depends on the pressure in the air tank, the air leakage and the volume of the building".
Tracer gas test , 
This test method entails introducing a small amount of tracer gas into a structure, thoroughly mixing it, and measuring the rate of change (decay) in tracer concentration. The air change rate can be estimated from the decay rate of tracer concentration with respect to time. Onsite meteorological conditions are measured concurrently. In the on-site monitor variant, tracer concentrations as a function of time are measured on site as air samples are obtained. In the container sample variant, after the tracer gas has thoroughly mixed, an initial air sample container is filled. The tracer gas is allowed to decay for a period of several hours during which a second and perhaps third sample container is filled. The air change rate can be determined from the decay in tracer concentrations.
 International Organization for Standardization, "ISO 9972:2015. Thermal performance of buildings — Determination of air permeability of buildings — Fan pressurization method", 2015
 David Keefe, "Introduction to Blower Doors", Home Energy. January/February 1994.
 T. Lanooy, W. Kornaat, N-J. Bink , W. Borsboom, "A new method to measure building airtightness", 39th AIVC Conference "Smart Ventilation for Buildings", Antibes Juan-Les-Pins, France, 18-19 September 2018.
 Jens Couckuyt, "Experimenteel onderzoek bij luchtdichtheidsmetingen: vergelijkende studie tussen traditionele Blowerdoor en vernieuwende Pulse test". Ghent University, 2018.
 E. Cooper, X. Zheng, C. Wood, M. Gillot, D. Tetlow, S. Riffat, L. De Simon, "Field trialling of a new airtightness tester in a range of UK homes", 36th AIVC Conference " Effective ventilation in high performance buildings", Madrid, Spain, 23-24 September 2015.
 ASTM, "Standard test method for determining air leakage rate by tracer dilution", ASTM Designation E 741-83, August 1987.
 M.H. Sherman, "Tracer-gas techniques for measuring ventilation in a single zone", Building and Environment, Vol 25, No 4, pp 365-374,1990.
 A. Vega Pasos , X. Zheng, V. Sougkakis , M. Gillott , J. Meulemans , O. Samin , F. Alzetto , L. Smith , S. Jackson , C. J. Wood, "Experimental study on the measurement of Building Infiltration and Air Leakage rates (at 4 and 50 Pa) by means of Tracer Gas methods, Blower Door and the novel Pulse technique in a Detached UK Home", 39th AIVC Conference "Smart Ventilation for Buildings", Antibes Juan-Les-Pins, France, 18-19 September 2018.
 M.J. Limb, "TN 55: A Review of International Ventilation, Airtightness, Thermal Insulation and Indoor Air Quality Criteria", AIVC Technical Note 55, 2001
- Corbett Lunsford, "Tracer Gas Test", Home performance, YouTube, 2018