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Blower Door Test   DW Energy Advisors

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Blower Door Test

To perform a thorough energy efficiency analysis of your home, energy advisors use specially designed "blower door" test equipment to measure your home's rate of air leakage.

The blower door is a variable-speed fan mounted on an adjustable panel that can fit into any exterior door opening of your home. Here’s how the test is run:

  1. Reduce house pressure. When the fan is turned on, the pressure inside your home is gradually reduced to allow outside air to flow into the house through unsealed openings or cracks in the house structure.
  2. Measure airflow rate. Pressure gauges connected to the fan measure the rate of airflow required to keep your home at a constant pressure so that the advisor can calculate your home's resistance to air infiltration.
  3. Calculate energy efficiency. The results of the test are incorporated into your home's energy efficiency rating. Because airtight homes are energy efficient, a house that has little air leakage will result in a higher rating than a home that has a lot of air leakage.
  4. Check ventilation. Advisors also ensure that the home is adequately ventilated as part of their analysis because modern airtight homes must always be adequately ventilated, usually with mechanical ventilation.

As part of the EnerGuide rating service, the blower door test is performed after the house has been built so that the "as built" results of the test are incorporated into the rating and the new house label.

How Blower Door Tests Work

A basic blower door system includes three components - a calibrated fan, a door panel system and a device to measure fan flow and building pressure.. The blower door fan is temporarily sealed into an exterior doorway using the door panel system. The fan is used to blow air into or out of the building which creates a small pressure difference between inside and outside. This pressure difference forces air through all holes and penetrations in the building enclosure. The tighter the building (e.g. fewer holes), the less air you need from the blower door fan to create a change in building pressure.

Blower door airtightness measurements are presented in a number of different formats including but not limited to:


 Air Flow (CFM)

CFM50 is defined as the air flow (in cubic feet per minute) needed to create a 50 Pascal pressure change in the building envelope.CFM50 is one of the most basic measurements of airtightness. Air flow measurements are sometimes referenced to different building pressures such as 25 or 75 Pascals.


 Air Changes Per Hour at 50 Pascals

In order to compare the relative airtightness of buildings, it is useful to normalize the measurements for the size of the building. This allows easy comparison of various sized buildings to each other, or to program guidelines. One of the most common ways to normalize building airtightness is to calculate the number of times per hour that the total volume of the enclosure is changed, when the enclosure is subjected to a 50 Pascal pressure difference. To calculate air changes per hour, the total volume of the enclosure is required in addition to the CFM50 measurement. It is also common to use the building enclosure surface area to normalize airtightness measurements.

Leakage Area

Leakage area estimates are a useful way to visualize the cumulative size of all leaks or holes in the building enclosure. Estimated leakage areas can also be used in infiltration models to estimate natural infiltration rates (i.e. the air change rate under natural weather conditions). In order to accurately estimate leakage areas, it is best to conduct the blower door test over a wide range of building pressures (e.g. 60 Pa to 15 Pa). There are a variety of standard calculation methods used to calculate leakage areas.




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Last modified: 04/24/08