March 31, 2017
A constant stream of evidence confirms performance losses up to 30% from roof curbs due to poor manufacturing, installation, or maintenance. Such curb defects reduce the performance of a 14-EER unit to a system performing below 10 EER. The problem is, unless you look for it, curb defects and the resulting efficiency losses are invisible.
How Does a Curb Function?
Roof curbs are accessories resembling a pedestal that sit below a rooftop-packaged unit. A well-designed and installed curb provides a transition for the supply and return air from the unit to the air distribution system.
In theory, a properly built and installed curb should have little effect on airflow through the system. In an ideal world, there should also be no temperature change through the curb. However, any difference in the air temperature entering or leaving a curb signals the possibility of leakage from outside the curb into the airstream. It can also indicate air bypassing between the supply and return ducts within the curb.