Energy Audit-Comparing a Great Blower Door Test to a Code Minimum Test

I recently blower door tested the tightest new home I have tested to date.  .82 air changes per hour at 50 pascals (ACH50), nearly one-quarter of the code required 3 ACH50 requirement.  After the test, the builder and I decided to open a window to see how much additional leakage it would take to get the home to the code minimum 3.

A little info about the home, new construction slab on grade with an attached heated garage.  The home has 2608 square feet and a volume of 24387 cubic feet.  We achieved 332 cubic feet per minute(CFM) moving through the fan giving us the .82 ACH50.  My Tectite software estimates the total size of the hole at 4 Pascals at 19.2 square inches or approximately a 4 inch by 5 inch hole in the building envelope.

To reach the 3 ACH50 code requirement, we would need to increase the air leakage to 1250 CFM across the fan.  The hole would increase to 72 square inches or an area of 9 inches by 8 inches.  We ended up opening a 32″ x 52″ casement window several inches.

The photo above shows how far the window needed to be opened to achieve a code minimum blower door test.  The amount of air moving through the opening would blow your hair back.  Now, imagine having a window open that far when it’s -20°F.  This would have a major effect on both heating costs and comfort.  Of course when the leakage is scattered around the house, you notice it less, but the fact is the code minimum leakage rate is still leaking that much air.

If you’ve been following me on Instagram, you may know that I have a project I’m currently working on called the #codeminimumhouse.  This new construction home is being built on a tight, low as possible budget.  Working with the homeowner and building contractor, I was able to have a few details added that will decrease the air leakage rate without adding much cost.  I performed a BEopt calculation (modeling software) that indicated a 6% reduction in heating and cooling moving from a code minimum 3 ACH50 to 1ACH50.  Not a lot of savings at today’s energy costs, but the decrease will also add comfort and improve indoor air quality.  Stay tuned for future blog posts on the details used in this new build.

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