What is a Blower Door Test?

You may have heard of a blower door test. But what is it exactly? You may consider using this diagnostic tool to assess the air tightness of your home and determine whether you need to improve it. The team at Fan Man, Inc. understands the importance of energy audits, which we perform, to help homeowners improve the energy efficiency of their homes. An audit can include a blower door test, duct leakage testing, combustion analysis, thermal imaging, and more.

Our team wants to help you ascertain your home's energy efficiency, and a blower door test can help with that. In this article, we will describe what the test is, the purpose of the test, and how it can help you evaluate the level of energy efficiency in your home.

The Purpose of a Blower Door Test

Home energy professionals use a blower door test as a diagnostic tool to determine how much air is entering or escaping from a home. In other words, a blower door test indicates a home's air tightness. The test utilizes diagnostic information to identify areas of air leakage and make energy-saving improvements.

What is a Blower Door?

A blower door is a machine that is used to depressurize or pressurize a home or building. It is used to detect air leakage pathways and measure the air tightness and the airflow of the building. Though the blower door has been more commonly used in residential settings, it is quickly becoming an essential tool in the commercial market as well. 

The blower door has a variable speed fan to induce a range of airflows to pressurize or depressurize most any size building or structure. A pressure gauge (a manometer) is used to measure both the pressure differential that flows across the face of the fan and across the building envelope to detect airflow. A mounting system holds the door in place for testing.

The Importance of Air Tightness

These are some reasons for establishing the proper building tightness:

• Reducing energy consumption from excess air leakage
• Improving indoor comfort
• Ensuring better indoor air quality
• Avoiding moisture condensation problems
• Avoiding uncomfortable drafts caused by cold or warm air leaking in from outside
• Proper sizing for your HVAC system
• Controlling outdoor contaminants, pests, and odors from entering your home.
• Determining proper sizing and airflow requirements of heating and cooling equipment.
• Determining whether mechanical ventilation is needed to provide acceptable fresh air and maintain indoor air quality in your home.

Note that North Carolina requires all new construction to pass a blower door test to meet energy efficiency standards.

How a Blower Door Test is Performed

Blower door testing involves using a special fan system to measure the air pressure within the home. By simulating outdoor conditions, technicians can evaluate how much air is escaping through doors, windows, and various other openings. This includes finding leaks in the duct system, which can be a major cause of energy loss.

The built-in fan blows air into or out of a home to create a positive or negative pressure difference between the inside and the outside of the structure. This pressure difference is typically 50PA or 1.57 psi for a standard blower door test. The process is based on the principle that the tighter the building, the less air is needed from the blower fan to create a change in building pressure. 

Testing is accomplished by operating the blower door manually or with the aid of data acquisition and fan control software. The speed of the fan, in cubic feet or air per minute to hold a 50 Pa pressure difference, is recorded as the CFM50 value. Alternately, this number can be divided by the air volume of the building to get the number of changes per hour, recorded as the ACH50 value. The blower door, in combination with an infrared camera, can be used to pinpoint the sources of air leakage, as shown in the IR-camera photo of a window during a blower door test. 

Source: Wikipedia

What Causes a Blower Door Test to Fail

It is estimated that 50% of newly constructed homes fail the blower door test. Most blower door tests fail because of a lack of understanding of the necessary air-sealing methods to create a continuous air barrier system.  

Commonly, blower door tests fail because of unsealed envelope penetrations, with the three main contributors being: 

• bath fans 
• sprinkler head
• fireplace inserts 

Bath fans have an exhaust with a backflow prevention device. Sometimes it is missing when installed, allowing air to flow into the home. Sprinkler pipes and ceiling lights in attics are often not properly air-sealed, allowing air to leak in. Fireplace inserts are often installed without being properly air-sealed. When it is permitted, it is good to place caps over ceiling fan vents to reduce or eliminate airflow during testing.

How to Pass a Blower Door Test

To pass a blower door test, perform these steps to ensure your home is properly sealed before the test.

• Identify Leak Points: Use a blower door to create a pressure differential. Then use a smoke pencil or infrared camera to locate air leaks around windows, doors, electrical outlets, and other penetrations.
• Seal All Gaps: Apply caulk or weatherstripping around windows and doors, seal gaps around electrical outlets, plumbing pipes, and foundation walls with expanding foam, and seal attic access hatches with weatherstripping or gaskets.
• Check for Penetrations: Pay close attention to areas where utilities enter the house, for example where pipes or wires pass through walls or floors.
• Prepare for the Test: Before testing, close all interior doors, turn off all fans and HVAC systems and seal any fireplace dampers.
• Professional Assistance: Consider hiring a certified home energy auditor such as Fan Man, Inc. in the Charlotte area to perform the blower door test and identify areas that need improvement.

Concentrate on these areas during sealing:

• Windows and doors
• Foundation walls
• Attic access
• Electrical outlets and switch plates
• Ductwork 
• Chimney

Who Needs a Blower Door Test

Anyone building a new home or significantly renovating an existing home should get a blower door test, as it is typically required by building codes and is crucial for identifying and addressing air leaks to improve energy efficiency and indoor comfort. If you are interested in maximizing your home’s energy performance, you should consider getting a blower door test.