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Field Test Best Practices: A Resource for Practical Residential Building Science

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Leakage and Infiltration

A cornerstone of energy efficient buildings, in both new and renovated existing homes, is having tight envelopes and effective air distribution systems. Leaky buildings waste energy spent on space conditioning as the conditioned air can escape. However, once you have built a tight building, well-controlled fresh air needs to be brought into the house and distributed uniformly within a home. There are a number of short term tests that are used to quantify the air tightness of a home and duct system and to determine the distribution of outside air.

The blower door and duct pressurization tests use similar equipment to pressurize or depressurize the whole house or the duct system, respectively, to measure leakage. The flow rate of air required to maintain a certain pressure can be used to characterize the total leakage area of the house or the duct system. Tracer gas tests provide a more accurate test method, and use the decaying concentration of a harmless gas to calculate ventilation rates.

Blower Door Test

A blower door is a device used to pressurize or depressurize a house to determine the leakage characteristics of the building envelope. A variable-speed fan is temporarily mounted in a doorway or other opening to pressurize (or depressurize) the house by specified amounts. The flow rate through a calibrated orifice is measured at the different house pressures. The relationship between flow rate and pressure difference is an indication of shell air-tightness.

Duct Pressurization Testing

A duct pressurization test is used to evaluate leakage of an air-distribution system, including the ducts and air handler cabinet. During the test, all supply and return registers are taped closed, and the pressurization fan is temporarily mounted to pressurize the taped-off duct system. A multipoint test can be performed to infer a leakage area, but it is more common to pressurize to a reference pressure of 25 Pascal (Pa).

Tracer Gas Testing

Blower door and duct pressurization tests provide measurements of the leakage characteristics of the envelope and air-distribution systems at elevated and uniform pressure differences, but may not be accurate for predicting how much outside air actually enters a house under particular driving forces. Tracer gas measurements can provide such direct measurements [1]. Single zone tests measure the net whole-house air exchange rates under a variety of operating conditions. Multi-zone tests provide additional insight into how outside air is distributed room to room inside the house. Inside and outside temperatures, as well as outside wind speeds, should be measured during the tests.