22 ACH – Leaky House

As you may know, we are pursuing the Passive House Certification.  One of the criteria is airtightness, targeting 0.6 air changes per hour (ACH) at 50 pascals.  This is pretty darn tight.  I’ve heard that a typical new home built today in the US is measured at about 6 ~ 7 ACH.  So we are trying to get our remodeled home to be 10 times more airtight than that.

So, we know that our house built in 1922 is quite drafty.  How drafty is it?  We decided to find out.  To establish the “before remodel” baseline we did a blower door test on Monday, 11/28/2011.  This was done using a blower door, which is a device used to measure the air leakage rate by pressurizing and depressurizing the building.  We did the pressurized test.

After the technician from Allterra Environmental fitted the frame and flexible panel to the front door he slowly cranked up the fan speed and we watched the numbers on the meter rise up and up and up….

The top number 49, is in pascal, a unit of measure used for pressure measurement.  The bottom number is the volume of air movement measured at cubic feet per minute (CFM).  When the picture was taken there were 5,390 cubic feet of air moving out of the house every minute.

How do you convert 5390 CFM at 49 pascal to air change per house (ACH)?  Well, you first multiply the the CFM number by 60 (because 1 hour has 60 minutes) and divide the total by the volume of the house.  The real estate report showed the house to have an area of 1574 square feet and the average ceiling height of the house is 9 feet, so the volume of the house is 14,166 cubic feet.

So, the ACH is (5,390 x 60) / (1574 x 9) = 22.83

I’ve heard that 50 pascal is equivalent to having 20 mph wind blowing outside.  So this means if we had constant high winds of 20 mph the house would completely exchange the air in the house over 22 times. That’s leaky….. and cold!

You can find out more about the history and the basics of blower door at this link.

Here’s a snapshot from the report: