As installers, many times we take the easiest way to complete our installation process. And sometimes a simple process goes bad and causes plank(s) replacement. Here’s a typical example. When we look at the photo of this job from the top view, you can clearly see the split on the long side of the vent. When you look closely at the side view, you can see the flooring has been undercut with a table saw. Typically this undercut will run 1-inch-plus depending on the flooring thickness. When the flooring goes through climatic changes, especially in low RH conditions, the wood will contract. With the wood being undercut, the stress from contraction was enough to cause this wood to split within the table saw cut.
When a forced air HVAC system does not have supplemental humidification, it is not uncommon that the relative humidity may be 20% or lower coming out of the duct. The concentration of dry air in the duct here caused the wood to contract and split within the saw cut. This is pretty much guaranteed to occur when the flooring is undercut like this—whether the flooring is solid or engineered.
The easiest way to prevent this from occurring is starting and stopping your side cuts ¾ inch from 90-degree side cuts. This way the undercut on the bottom of the plank is minimal and won’t cause vent-splitting concerns.