Arkansas HVACR NewsMagazine November 2024

HVACR NewsMagazine November 2024 Tech News

Hopefully everyone in the HVAC industry has put their hand on a flow hood at one time or another. The tool is used to validate room by room air flow generally. Without utilizing the flow hood, it is impossible to guess air flow

(7% in some jurisdictions) leakage is commonly acceptable, much better performance (5%) is possible on homes less than 2000 square feet. Most crews test to meet passing criteria, and this is wrong. If 10% duct leakage is a target to pass inspection, they cease sealing once we hit 10%. If your company employs proper sealing techniques and follows the process from one end of the

delivery. The flow hood was invented about 1979 or when Cabbage Patch Dolls were the rage, but strangely no one takes credit for the invention as it was initially considered unreliable. Probably due to resistance from our own industry. We hate slowing down

distribution to the other, the duct blower will be a tool that confirms the job is done correctly.

installations just to get them right. The flow hood of today has vastly improved since its initial adoption and is now utilizing better hardware and software technology. Yes, there are alternatives to flow hoods available but in the real-world flow hoods work well with minimal training. Due to code requirements that are associated with minimal duct leakage, more folks are familiar with the duct blower. A simple description follows. A small fan is set up to the return side of the distribution system by way of a 10” flexible duct. Two small tubes (probes) are utilized to capture pressure differentials. One tube is placed on the supply side of the duct distribution system and the other runs to a port on the fan itself. With all registers sealed, the fan is turned on and a negative pressure of 25 paschal is exerted on the duct to measure pressure differentials of the probes. The provided manometer has software that computes the differentials and formulates actual duct leakage. While 10%

We have witnessed companies that never employ the duct blower until the inspection is done by a third party. With several hundred jobs performed, the ratio of underperforming duct leakage is less than three percent testing failure rate. The best practice remains to seal to the best of your ability and be surprised by how low you can go once you break out the duct blower. Fewer HVAC techs or installers have ever put their hand on a blower door. The door is a

more complicated set up than using a duct blower, although similar technology is shared between the tools. The blower door originated in Sweden in 1977 as a blower window. The blower window was brought to the US in 1979 by