Using a Blower Door
This versatile diagnostic building tool may look intimidating, but it’s actually pretty easy to use.
Blower doors are probably the most-important building diagnostic tool there is. Builders, weatherization professionals, and energy auditors use blower doors to track down air leaks and do airtightness testing. In this episode of Tool Tech, host Patrick McCombe shows you how to prepare for a blower door test and then tests his own home using a Minneapolis Blower Door with a DG700 air-pressure gauge.
Prepping for the test
The first thing you have to do is turn off any combustion appliances. If you don’t, the blower door could cause these appliances to backdraft and bring carbon monoxide into the house. You also want to make sure there isn’t a fire or hot embers in the firebox or the blower door can suck the embers into the house. You’ll want to clean up any ash that’s in the firebox so it doesn’t blow around the house.
Next, walk around the house and make sure the windows and exterior doors are closed and all the interior doors are open. You also should open the basement door if you have basement access from inside the house. You must turn off any exhaust fans, like the range hood and bath fans.
Performing a basic airtightness test
The first step is to assemble the aluminum frame and size it for the opening. Connect the aluminum extrusions on top of the fabric panel, so you don’t scratch the floor. Once the frame is sized for the door opening, lay it back down on the panel and fasten the velcro tabs. Now put the door panel into the door and snug it in position with the locking knobs. Before placing the fan into the elastic hole, run the green tubing outside through the hole in the bottom of the fabric panel. Make sure the end is away from the fan’s airstream and strong winds. Now insert the fan with all the flow rings and no-flow cover into the blower door. Make sure the flow rings are facing the home’s interior. Hang the speed controller onto the frame and plug the speed controller into the fan. Connect the power cord to an outlet.
Now hang the gauge from the frame and connect the red hose to the B-channel input tap. The B reference tap is left open. The green tube goes on the A-side reference tap and the input tap is left open.
Establish the baseline for the manometer by following the instructions included with the kit.
With the appropriate flow ring in place, slowly increase the fan speed, trying to achieve between -45 and -55 pascals. An airtightness test is always expressed in air changes at 50 pascals of pressure. The manometer automatically expresses on the B channel what the leakage rate would be a 50 pascals, even if the fan isn’t depressurizing the house to this exact amount. Once you have the CFM number, write it down and multiply it by 60, the number of minutes in an hour. Then divide that number by the home’s cubic feet. You determine the cubic feet of conditioned space by measuring the length, width, and height of the interior. Include the basement if it’s conditioned space. The final result will be the number of air changes per hour (ACH) at -50 Pascals of pressure, or ACH50.
Senior editor Patrick McCombe has been testing power tools on behalf of national publications for more than 15 years, and he regularly meets with product manufacturers to try out new introductions. In the Tool Tech series, Patrick reviews the latest tools and materials, discusses building technology, and shows time-tested techniques for better, more-efficient home building. Consider becoming an online member to watch other Tool Tech videos.