Excerpt: "Timber floors with under floor heating (UFH) systems represent a new and growing trend for the hardwood flooring market in Australia’s southern states. These systems are common in North America and Europe, but experience in Australia is limited with much debate concerning the suitability and performance of Australian flooring material in this application. Installing a wooden floor over a heated surface will lower the expected in-service Equilibrium Moisture Content (EMC), thus floors with UFH should be installed at a lower Moisture Content (MC) than floors with no such heating system."
RBc: There are few better documents adressing the use of radiant floors with hardwood than R. Farrell and S. Gadient's research report for the Centre for Sustainable Architecture with Wood.
If you don't want to read the entire 88 page report, the last words in the conclusion reads, "Wooden floors over UFH can perform well, and could even be argued that a wooden floor installed and operated correctly will out-perform those with conventional heating systems that cause hot-spots in the floor with extreme localised dimensional change. A wooden floor with UFH operated with moderate and gradual temperature changes will apply constant and even heat to the floor avoiding problems associated with localised heating."
Source and credit:hardwood with radiant heated wood floors.
Suggested study: Heat Loss to Head Loss - The Radiant Design Guide