Tools for Testing Pressure and Air Leakage

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Air sealing specialists in the past few years have developed more sophisticated ways to determine how much leakage is in a house, where that leakage is, and how tightening a house will affect house pressures.

Testing House Leakage

The blower door is a tool that measures air leakage in your house. It consists of a fan that fits into a door frame. The instruments on the blower door measure how much air the fan must blow to make the house reach a certain air pressure. While the blower door is running, air will rush through every leak. Infrared cameras and smoke sticks can be used to find these subtle air currents—and pinpoint the leaks.

Blower doors can be used in conjunction with a separate pressure gauge, or manometer, to determine the difference in pressure between the house and another space—for example, the attic, garage, crawlspace, or basement. This tells the technician how effective the air barrier is between these spaces. The manometer can also be used to measure differences in pressure between two rooms. From this the technician can tell, for example, whether closing the door to a bedroom when the heater is running pressurizes that room.

Testing Ducts

The blower door can be used to get a rough estimate of leakage in heating and cooling ducts. But there are also specific tools used for testing ducts.

Pressure pans are used in conjunction with a blower door. A pressure pan looks like a cake pan with a pressure-sensing tube through it. The tube hooks up to a manometer. The technician holds the pressure pan over a duct register to get a pressure reading in that particular duct run. This is a very useful tool for targeting which ducts are most in need of being sealed.

To measure duct leaks more accurately, the technician may use either a duct leakage tester or a flow hood. A duct leakage tester works like a miniature blower door. It has a fan that blows air into the duct system, and instruments that estimate leakage. When the duct to one register is being tested, all other registers are taped off. A flow hood is held up to supply or return registers while the air handler is running to measure the air flow. By measuring the air flow at the heater or air conditioner itself, the technician can tell how much air is being lost to leakage.

A duct leakage tester can also be used in conjunction with a blower door to isolate how much of the duct leakage is going outside the house. Duct leaks to inside the house are not as important as leakage to outside.

Your contractor may not have all of these devices. But a good contractor will have some combination of tools that enables him or her to measure the leakage in your house and ducts and to make sure that air sealing doesn't cause a backdrafting hazard due to changed house pressures.

Keep in mind that houses are complex and each one is different. It's important that technicians take the time to do the job right.

Excerpted with permission from No-Regrets Remodeling by Home Energy (1997)