Advanced research into floor performance issues: The effects of heating systems on floor performance in cool temperate climates

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.

This study assesses the performance of backsawn Blackbutt (Eucalyptus pilularis) and quartersawn Messmate (Eucalyptus obliqua) flooring material in an UFH application. 19mm strip and 12mm overlay floors from each species were built in separate test chambers and subjected to different heating intensities. The first part of the study monitors a heating period where the heating has been switched on (simulating winter conditions). In the second part of the study the heating is turned off to monitor floor behavior in non-heated summer conditions. Sub-floor, chamber, external temperature and relative humidity conditions were monitored on a continuous basis, with periodic measurement of floorboard MC, cover width, gapping and cupping. The performance of each floor was assessed for the duration of each heating cycle and the results presented and discussed.

The results of this study show that 19mm Blackbutt and Messmate flooring can perform well in an under-floor heating application under the conditions tested. Backsawn 12mm Blackbutt flooring exhibited a high degree of cupping during the trials and is not recommended for use in such an installation. Due to the greater stability and resilience of thicker boards it would be prudent to avoid using 12mm overlay flooring with under-floor heating until their performance in such systems are more fully understood. However, as gluing was not a feasible fixing method for the 12mm overlay in this trial, it is acknowledged that an UFH system that facilitated gluing may have produced different results. As is often stated in international literature, narrow boards are preferred to wide to avoid excessive gap widths. During the trials no edge bonding occurred suggesting that sealing the floors before installation is good practice. Maintaining a minimum level of heat during unoccupied winter periods and avoiding abrupt changes in heating temperatures would constitute good practice in terms of floor performance.

Recent energy crises have refocused attention on energy efficiency issues across the globe. Building insulation and heating will likely come under greater scrutiny and the cooler southern climates of Australia may expect changes in these areas. The increased thermal comfort offered by radiant UFH systems is likely to further their popularity. It would be prudent for installers of wooden floors to anticipate such changes and ensure that species choice; cover-width, and installation procedures are selected to maximise the performance of wooden floors in such applications. Indeed by avoiding hot-spots that can be associated with forced air heating systems, properly installed and controlled UFH applications may even help guarantee wooden floor performance relative to other “localised” forms of space heating by providing more even and stable conditions.