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BPI Written Exam - Section 3 Measurement & Verification of Building Performance

1. Application of Measured Air Leakage Test Results

Air leakage is reported in CFM50, or cubic feet per minute (a flow rate) at 50 Pascals. Air leakage results should be compared to the Minimum Ventilation Requirements (MVR) according to BPI Standards and set by ASHRAE 62.2 to tell if the home is too tight or can be safely air sealed and by how much.

Using a blower door, we can set a pressure differential between inside and outside. Once the home has been set up for blower door operation and the fan is up and running, we can easily find the location of air leakages with the following tools.

Our hands are the quickest and easiest way to simply feel air flowing through cracks to the outside. By wetting your hand, you can discover less noticeable leaks. By closing a door or partially closing interior doors, you can compare the air leakage of each room to one-another.
Smoke pens will put a puff or stream of odorless smoke into the air and the air will take the smoke in the direction of air flow, either towards the middle of a room if pressurizing or the smoke will get sucked outside if depressurizing.
Infrared cameras can show the cold / hot (depending on the season) air coming into the home through air leakage sources. IR cameras do not show insulation misalignments or missing insulation when in use at the same time as the blower door.
Pressure mapping can be extremely helpful to quantify how leaky an inaccessible wall chase, archway or column is without having to tear drywall down. In balloon framed homes, it can let you know if a drywall needs to come down before you assume that the wall cavity needs to be capped and air sealed.

“Homes with more than 6,000 CFM50 may merit days of labor and hundreds of dollars of materials,” write energy experts John Krigger and Chris Dorsi in their book, Residential Energy. “Homes with 1,500 CFM50 are difficult to improve.” You can use the following two formulas below to calculate how much air leakage is costing a homeowner during heating and cooling season from Lawrence Berkeley Labs.

How Much Is Air Leakage Costing Homeowners?

Heating season
26 × HDD x fuel price x CFM50 ×0.6 / N x seasonal efficiency

Where:
HDD is the annual heating degree days (base 65° F) for the building location
Fuel Price is the cost of fuel in dollars per BTU
N is the Energy Climate Factor from the Climate Information Screen
Seasonal Efficiency is the AFUE rating of the heating system

Cooling season
0.026 × CDD × fuel price × CFM50 / N x SEER

Where:
CDD is the cooling degree days (base 70° F) for the building location
Fuel Price is the cost of electricity in dollars per kWh.
N is the Energy Climate Factor from the Climate Information Screen
SEER is the SEER rating for the air conditioner

What do you do once you find air leakage in a home?

Once you find how leaky the house is and where it is coming from we need to come up with a plan to to seal the air leakage. In humid climates air leakage has a higher importance because moisture is damaging because all it takes is a small amount of air leakage to let humid air into the duct system and wall cavities, potentially causing mold and rot. Now now all homes are rotting away because of air leakage but we all know it is a frequent problem. Finding the source of the moisture is key, then eliminating it or mitigating it away from the house and air leakage points will minimize waters damaging effects. Moisture may come from air handlers located in crawl spaces, closets or attics, improper drainage away from the house, bad roof slope design, or leaks at plumbing lines or vents.

Once moisture is mitigated you are free to air seal. Air sealing should be done with a rigid material like foam board or drywall for capping large penetrations or spray foam or Pookie for smaller leakage around top plates and to seal around foam board.

Air leakage that is visible or accessible is the easiest to tackle. Punch lists and maps should be developed for the crew of exactly where the leakage needs to be sealed and with what material. Where air leakage was found with pressure mapping within walls, a plan should be created to access and seal the wall cavity and a back up plan should be done in case the first drywall cut does not capture all the intended leaks. Blower door testing should also be done in conjunction with air sealing to measure that improvements were made on the spot. That way, more work can be done without having the drywall replaced.

See also:
Blower door guided air sealing techniques - http://www.bpiexamacademy.com/5-blower-door-guided-air-sealing-techniques.html

How to control ventilation once the house is sealed - http://www.bpiexamacademy.com/4-understand-importance-of-air-leakage-control-and-remediation-procedures.html

Retrotech's guide to air leakage - http://retrotec.com/sites/default/files/manual-guides-specs/Manual-Residential%20Pressure%20&%20Air%20Leakage%20Testing.pdf

Pressure mapping - http://www.bpiexamacademy.com/15-pressure-boundary.html
- http://www.bpiexamacademy.com/5-blower-door-guided-air-sealing-techniques.html

Next Section

3a. Applied diagnostics and troubleshooting