I mentioned the blower door test, which is one of the insulation rebate requirements. To quantify the energy savings we need to conduct one blower door test prior and one after the insulation installation.
What is a blower door test?
A blower door test depressurizes the building (typically to 50 pascal) and measures the resulting air flow in and out of the building. This test establishes how air tight a building is, and/or allows the detection of air leaks that need to be fixed.
Why do air leaks or air tightness matter? Because unwanted air movement can significantly negate the effect of insulation. The classic example is batt insulation in a stud wall. If cold or hot air can blow through the insulation batts, they have little insulation value.
Depressurizing the building sounds complicated, but is relatively straight forward. It starts with an adjustable metal frame that can be fitted into a door, typically the front or back door. Before the fitting, the frame gets wrapped into a cover, which has a hole toward the bottom for a powerful fan that will take care of the depressurizing.
Measuring the pressure differentials and air leakage is a little more complicated. It requires a sophisticated pressure and flow gauge which is mounted on the inside of the blower door, and a few tubes.
You may have noticed in the video above the small green tube that John placed on the front porch and through the fan opening. That tube references the pressure outside the building and connects to the gauge, which at the same time measures the pressure inside the building.
To measure the airflow, the gauge measures again the pressure inside the building and references it against the pressure inside the fan, which is connected to the gauge with a small red tube.
Conducting the test
We were almost ready to go, except for a few more items that needed to be checked:
- Close all windows and exterior doors (except the one with the blower door).
- Install all deadbolts and door knobs in exterior doors, or seal over them (in our case, the back door leading to the porch).
- Seal all ventilation terminals (HRV and range hood).
- Fill all dry P-traps with water – sinks, showers, floor drains, etc.
- Seal any conduits connecting the basement and first floor to the second floor.
- Turn off heating equipment or water heaters (did not apply here as the heating equipment is located in the basement, not the 2nd floor, which we were testing).
One note on the numbers shown on the pressure and flow gauge: The number to the left shows the pressure reading (in pascal), and the number on the right shows the airflow in cubic feet per minute (cfm).
The first test results
Our official reading for the 2nd floor was 4,763 cfm at 50 pascal (4,763 cfm50).
Another metric that is used is air changes per hour at 50 pascal (ach50). To convert to an ach50 value, I multiply the cfm50 reading by 60 (60 minutes) and divide the result by the building volume (20,608 cubic feet for the second floor).
4,763 cfm50 * 60 minutes / 20,608 cubic feet = 13.9 ach50
In translation: While the 2nd floor is depressurized to 50 pascal, its entire air volume is exchanged almost 14 times per hour.
4,763 cfm50 or 13.9 ach50 appear to be high numbers but are not that uncommon for old buildings like ours. Here is what John from Chicago Home Performance, who did the blower door test, had to say:
Your house actually falls right in line with what I would expect with masonry buildings of similar construction type/age. I would say 7-15 ach50 is pretty normal depending on what has been done to the building over time. However, I have seen them as high as 20 ach50 in some really beat up places.
We have a pretty leaky 2nd floor. In fact, while we ran the blower door test, I walked around, felt the drafts and could easily follow them to their source. Take the unsealed gap between the 1st and 2nd floor for example…
… or the old double hung windows in the south wall.
Areas like this need serious air sealing. Some, like the old window, were sealed when we installed the replacement windows, while others, like the floor gap, wait for the closed cell SPF (spray polyurethane foam) application.
To learn more about blower door tests, visit the GreenBuildingAdvisor.com blog: Blower Door Basics.
Shrinking a long to-do list
Insulation preps – plugging the 3” gap
Insulation preps – 3” thermal break