Our previous post focused on the infrared thermal imaging scanner that we use to detect air infiltration into new and existing homes.
In this post we’ll focus on another of the diagnostic tools of the trade that we use to verify supply and return-air efficiencies in forced-air heating/cooling systems.
We use the Minneapolis Duct Blaster to perform a “Total Leakage Test” of the duct system.
The Duct Blaster is a device that uses pressure testing to find the amount and location of air leakage in a duct system.
To do the test, we seal all outlets except for one on the return side of the system. This is the side that returns stale air to the furnace to be reconditioned. The Duct Blaster is connected to this return-air opening and then turned on to blow air into the ducts. The air goes through the return ducts to the air handler and then through the supply ducts. If the duct system is very tight, it doesn’t take much airflow through the fan to pressurize the ducts. If you have a big leak, like a disconnected plenum or duct, it will be next to impossible to pressurize the ducts adequately. This would be like trying to pump air into a tire that has a big hole in it.
The process yields quantitative results because testing requires two pressure measurements: one inside the ducts and the other inside the fan. The first allows the tester to compare results from different systems by always pressurizing to the same level. The second measures the airflow in the fan when that level is reached. As mentioned above, tight ducts means low airflow, and leaky ducts require lots of airflow.
Pressurizing only the ducts determines the total leakage. That includes the air that escapes into the conditioned space and the air that leaks to the outside of the building envelope (i.e., the attic or crawl space). The latter is the most important part because you derive no benefit from it. To separate it from the total leakage, we pressurize the house to the same level as the ducts by using the Blower Door. Then, when the Duct Blaster brings the ducts up to the required pressure, none will leak to the inside of the house because it’s at the same pressure as the ducts. The fan only has to blow enough air in to make up for the leakage to the outside, and that’s the amount that’s important.
In a tight air distribution system, the leakage to the outside (in cubic feet per minute, or cfm) will be 5% or less of the square footage of the home. Most new installations start at about 15% to 20%, and go downhill from there. At those rates, a third of the heating and cooling bills could be a direct result of duct leakage.
After performing a Duct Blaster test to determine the amount and locations of air and duct leakage, we seal up the leaks that we find. Upon completion the house and/or duct system will perform better, and your heating and cooing bill will be lower.
You can follow this link to a you tube video part 1 of 4 videos.
As they say at Focus on Energy, “Testing Trumps Talk” and we couldn’t agree more.
By testing and verifying the tightness of the building envelope and the duct systems in our high-performance homes, we are able to identify any deficiencies and take corrective measures.
Lower operating costs, greater comfort, safety, durability and higher resale values are just a few of the benefits realized by implementing building science principles and best practices into the homes that we build.
By testing, inspecting, and documenting the quality of work, we bring a higher level of added value and peace of mind for our clients.
The Duct Blaster is another diagnostic tool of the trade that helps us in delivering the added value that is built-in to our high-performance homes and remodel projects.
If you’d like to learn more about how we can provide added value to your new home or remodel, please visit our website and contact us.
In our next post, we’ll talk about mechanical ventilation, exhaust equipment and the diagnostic tools of the trade that we use to verify performance and efficiency of this critical component of the high-performance homes we build.
Great Lakes Carpentry is “Building Today for a Greener Tomorrow.”