New Blower Door Test

Blower Doors: What Are They and How Do They Work?

A blower door is a powerful fan that a trained energy professional temporarily mounts into the frame of an exterior doorway in your home. After calibrating the device, the fan pulls air out of the house, lowering the air pressure inside. The higher outside air pressure then flows in through all unsealed gaps, cracks and openings such as gaps, cracks, or wiring penetrations. If conditions do not allow for lowering the pressure in the home, the fan may also be operated in reverse, with air pressure increased inside the home.

While the blower test is being conducted, the analyst may use an infrared camera to look at the walls, ceilings, and floors, to find specific locations where insulation is missing and air is leaking. The analyst may also use a nontoxic smoke pencil to detect air leaks in your home. These tests determine the air infiltration rate of your home, which is recorded on a laptop or tablet.

The blower door test is conducted as part of the energy assessment of your home. Your contractor may also operate the blower door while performing air sealing (a method known as blower door assisted air sealing), and after to measure and verify the level of air leakage reduction achieved.

Blower doors consist of a frame and flexible panel that fit in a doorway, a variable-speed fan, a digital pressure gauge to measure the pressure differences inside and outside the home, which are connected to a device for measuring airflow, known as a manometer. 

There are two types of blower doors: calibrated and uncalibrated. It is important that auditors use a calibrated door. This type of blower door has several gauges that measure the amount of air flowing out of the house through the fan.

Uncalibrated blower doors can only locate leaks in homes. They provide no method for determining the overall tightness of the home.

The calibrated blower door's data allow your contractor to quantify the amount of air leakage prior to installation of air-sealing improvements, and the reduction in leakage achieved after air-sealing is completed.

Building and mechanical codes mandate minimum air exchanges per unit of time. Requirements are generally expressed in Air Changes per Hour (ACH)—how often the total volume of air in a space is replaced—or in Cubic Feet per Minute (CFM) of outdoor air per person. 

The exact mandate depends heavily on the type of building and local regulations:

• Residential Homes: Codes like the International Residential Code (IRC) and standards set by ASHRAE mandate mechanical ventilation to ensure an adequate supply of fresh air. Standard requirements typically dictate a continuous rate of at least 0.35 ACH (or a specific CFM formula based on square footage and number of bedrooms).

• Commercial Buildings: Local codes, such as the International Mechanical Code (IMC), require minimum outdoor air ventilation based on room use and occupancy (e.g., specific rates for offices, classrooms, or gyms). For spaces like warehouses or workshops, general rules of thumb often require 4 to 6 ACH.

• Healthcare & Labs: Stringent standards (like ASHRAE 170) mandate high air change rates to control infection and dilute contaminants. For example, hospital operating rooms are often required to have 20 or more air changes per hour. 

A note on "Tightness":

Modern energy codes require building envelopes to be tightly sealed to save energy. If a blower door test proves a home is too airtight (usually below 5 ACH at 50 Pascals of pressure), the building code usually mandates the installation of a mechanical ventilation system to guarantee fresh air.