Radiant in-floor heating is an increasingly popular option for homeowners due to the underfoot comfort it provides. When hardwood comes into the picture though, radiant heat is not always compatible with every species and product out there.
As a general rule, solid hardwood is NEVER approved to install over radiant heat (unless specifically approved by the manufacturer of that floor). Solid hardwood products are not dimensionally stable enough to handle the rapid temperature and humidity changes that occur directly beneath it with an in-floor heating system.
Engineered hardwood opens the doors a bit on the radiant heat front; with a manufactured core and a hardwood veneer on the top these products are much more stable; but there are still some off-limits categories. The first one to come to mind is Hickory. Hickory products are nearly never approved over radiant heat systems and doing so can immediately void the warranty of a brand-new floor.
Hickory is a volatile species as far as moisture is concerned; it reacts to changes in humidity quickly and significantly. On top of being a very dense product this combination almost gives hickory "super floor" strength. Once the product begins to dry out it can begin to check, split, splinter and shear away from the core along with buckling and cupping if it takes on too much humidity too quickly. Due to this species being so unpredictable in a radiant heat application, engineered flooring manufacturers do not approve this installation.
If you’d like to read more about radiant heat and hardwood here is a great article from Brett Miller with the NWFA! The NWFA offers many great resources for technical information and installation!
A hickory hardwood product pulling away from the veneer