Today was the day the house squared up to the blower door, looked it in the eye, then ran it over Mack truck style.
Before getting to the gritty details, I'll say if you're hoping to read about how the blower door test was conducted with a repurposed squirrel cage blower from Harbor Freight and a manometer improvised with old test tubes and a length of surgical tubing this post will be a disappointment. It's not that it couldn't be done rather it didn't have to be done. For this test a professional with actual equipment was brought to bare.
Last week Chris of ReVision Heat dropped by to run what would be the first of two calibrated blower door tests (see figure 1 below). Two?! As it turned out the blower door setup Chris had on hand for the first test couldn't achieve flow rates low enough to get an accurate assessment of the amount of air the house was leaking once depressurized to 50 pascals. We did manage to get a reading with the house depressurized to three times the required amount (150 pascals). The reading was approximately 90 cubic feet per minute (cfm). Incidentally, our test limit for international Passivhaus certification is approximately 90 cfm. This was a good sign.
As an aside, depressurizing the house to 150 pascals was an interesting event in and of itself. We could hear the outside atmosphere crunching the house down onto the foundation. In addition, the blower door was severely bowed into the building. Chris had to actively hold the blower test rig into the door opening to keep it from being blown into the house. Really wild to to experience something like that apart from machines like airplanes or submarines that operate with significant differences in pressure between interior and exterior environments.
Today Chris returned with a few new test rig additions to give the house its second blower door test. We knew the house would perform well but didn't know how well until the test rig was installed and fired up. The results of the second blower door test are included below in figure 2.
The number on the left in figure 2 shows the pressure differential between the inside and outside of the building. Negative 50 pascals means there's more pressure outside than inside the house. The number on the right (47 cfm) is the rate at which air is moving through the blower door to produce a negative 50 pascal pressure differential. The maximum allowable is 91 cfm for our house. Right now the house is leaking air at about 0.3 Air Changes per Hour (ACH) or half the 0.6 ACH at 50 pascals allowed by the Passivhaus building standard.
OK. So, how big a deal is 0.3 ACH at 50 pascals? Here in the US the most stringent commonly enforced residential air infiltration requirement comes from the 2012 International Energy Conservation Code (2012 IECC). If we were building a house to meet 2012 IECC requirements we'd need less than or equal to 3 ACH at 50 pascals. Our house could leak ten times the amount of air it does now (910 cfm!) and meet the 2012 IECC limit. That's right. Ten times. In the US we'd be legal. In Germany we'd probably be thrown in jail.
Prior to 2012 a US residence could be built and never subjected to a blower door test. Think about that the next time you're plunking down a big greasy wad of cash to cover the heating bill in the dead of winter. Big wad means big air leaks.
Before getting to the gritty details, I'll say if you're hoping to read about how the blower door test was conducted with a repurposed squirrel cage blower from Harbor Freight and a manometer improvised with old test tubes and a length of surgical tubing this post will be a disappointment. It's not that it couldn't be done rather it didn't have to be done. For this test a professional with actual equipment was brought to bare.
Last week Chris of ReVision Heat dropped by to run what would be the first of two calibrated blower door tests (see figure 1 below). Two?! As it turned out the blower door setup Chris had on hand for the first test couldn't achieve flow rates low enough to get an accurate assessment of the amount of air the house was leaking once depressurized to 50 pascals. We did manage to get a reading with the house depressurized to three times the required amount (150 pascals). The reading was approximately 90 cubic feet per minute (cfm). Incidentally, our test limit for international Passivhaus certification is approximately 90 cfm. This was a good sign.
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| Figure 1: Chris of ReVision Heat Running Blower Door Test #1 |
Today Chris returned with a few new test rig additions to give the house its second blower door test. We knew the house would perform well but didn't know how well until the test rig was installed and fired up. The results of the second blower door test are included below in figure 2.
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| Figure 2: Second Blower Door Test Results |
OK. So, how big a deal is 0.3 ACH at 50 pascals? Here in the US the most stringent commonly enforced residential air infiltration requirement comes from the 2012 International Energy Conservation Code (2012 IECC). If we were building a house to meet 2012 IECC requirements we'd need less than or equal to 3 ACH at 50 pascals. Our house could leak ten times the amount of air it does now (910 cfm!) and meet the 2012 IECC limit. That's right. Ten times. In the US we'd be legal. In Germany we'd probably be thrown in jail.
Prior to 2012 a US residence could be built and never subjected to a blower door test. Think about that the next time you're plunking down a big greasy wad of cash to cover the heating bill in the dead of winter. Big wad means big air leaks.
