Over recent years and on many projects, we have found ourselves at the final hour informing the Mechanical Contractor that the current fan cannot satisfy the space requirements of the design, yet at the main traverse point, the volume far exceeds the main duty of the fan.
At this stage it is clearly evident that the system is subject to leakage and it becomes a frantic effort by all parties that are left on-site to find and fix these issues. And it is generally not just one large leakage point where this problem lays but many individual leaks that collectively attributes to the problem at hand. It is this predicament that becomes too onerous to overcome at this final stage of the project and generally results in an expensive outcome to make the installation compliant.
Clearly a situation that could have been tackled at the time of installation!
Although this is a repeating problem that we encounter on a frequent basis, some of the responsibility must lay with the designer, as it is generally his specification that states whether a ductwork system shall be leakage tested or not and generally, it states that low pressure ductwork falls outside the pressure class for leakage testing. Therefore as a result of this, most contractors do not see it necessary or as a requirement to test.
However, with the low pressure systems that we get to test, our findings on-site do not generally point to the installation, (although this varies from site to site), but generally points to the manufacture of the ductwork; with seams joints and the Mezz flanges being the common culprits.
So, although it may not be specified in the contract documents, we strongly recommend that it is in the interest of the Mechanical Contractor or even the Main Contractor, to sample leakage test a percentage of all pressure classes of ductwork. By doing so, they will gain confidence through the installation contractor that any latent issues will be minimised at the crunch time of the project.