Blower door test

Sharon and Andy from Block Energy Design showed up Tuesday morning to do a blower door test on the home. This test determines how airtight the home is. Here is a pic of the Minneapolis Blower Door, made by The Energy Conservatory, installed in the entry of the home.

All of the other windows and doors in the home were closed. The blower removed air from the home and maintained pressure inside that was 50 pascals (Pa) less than outside. This small pressure difference caused outside air to leak into the house through any cracks it could find. We could feel a small amount of air flow by the tops of the sliding glass doors.

It was determined that 95 cubic feet per minute (cfm) of air flow through the blower was needed to maintain a 50 Pa pressure difference. This measurement along with the interior volume of the home was used to calculate a value of 0.4 air changes per hour at 50 Pa (ACH50). Air changes per hour (ACH) is the number of times per hour the volume of air inside the home is exchanged with fresh or filtered air. A value of 0.4 ACH50 indicates extremely air tight building construction. A new home that is considered "well built" will change over this much air WITHOUT a blower creating a pressure difference. All of that time spent sealing up cracks with foam paid off. That is good news for energy efficiency.

ACH50 is commonly divided by 20 to arrive at a value for "natural" ACH (without the blower creating a pressure difference). That means my home naturally changes air over 20 times less than what is considered a "tight" building. This is great for keeping heat in the home, but can lead to poor indoor air quality (IAQ).

While building the home, I took precautions to ensure adequate IAQ such as:

• installing a French drain under the slab to reduce potential for radon gas inside the home
• installing only electric appliances - there are no combustion appliances which would create carbon monoxide
• using low or no VOC materials inside the home

Even so, carbon dioxide (CO₂) will buildup from human activity in the home, and mold can be an issue in moist areas like the bathroom. There are several things we can do to maintain acceptable IAQ given these potential pollutants.

• on sunny days, it is warm enough in the home to open windows
• on days when it is too cold or rainy outside to open windows, we should run the exhaust fan in the bathroom for an extended time period
• we could purchase and install a heat recovery ventilation system to exchange stale indoor air with fresh outside air while retaining most of the heat
• houseplants can help reduce certain indoor pollutants

We definitely notice the home is comfortably warm without using the radiant floor heat. We also notice that the air seems stale when the house has been closed up for many hours. Now we have some test data that explains why. Thanks for reading. Feel free to leave a comment.