Undesirable sound effects from ECOFILM C ceiling heating

We have recently received a complaint about unpleasant sounds emitted by ceiling heating using ECOFILM foil. The search for the cause led to a modification of the ECOFILM C foil mounting rules, which now prescribe the hanging of plasterboard ceilings on spring hangers.
Suspension of a CD profile on spring hangers – four-point
Direct suspension of a CD profile

The problem occurred with a standard KNAUF suspended ceiling. A relatively loud crackling and popping occurred at approximately two-minute intervals when the heating was switched on. The sounds began approximately 10 minutes after switching on the ceiling heating and stopped after approximately 30 minutes – i.e. they occurred as the ceiling heating warmed up the suspended ceiling to its operating temperature.  The sounds were heard again when the ceiling heating was switched off and the ceiling started to cool down. They could be heard mainly from the edge parts of the structure, though it wasn’t possible to localize the source exactly.

Even though the direct relationship between the sounds and the ceiling heating was undeniable, it was an unusual phenomenon which we hadn´t encountered previously. We therefore contacted the technical department at KNAUF and worked together with them to find the cause. We checked whether the ceiling is of the floating type, the way in which the plasterboard is anchored to the CD profiles, and whether the heating foil was in contact with the heating parts of metal components. Also, an additional expansion joint was added, the plasterboards were exchanged and the tightness of screws was checked. However, none of these measures achieved our aim, i.e. the elimination of the undesired noise, and so we constructed a test version of the suspended ceiling with heating foils in our testing room.

The construction was carried out in the same way as in the case of the problematic application, i.e. with KNAUF White boards, and with the suspended ceiling hanging via ‘direct suspension’. The sounds which brought about the complaint also affected this test version, and therefore several different alterations to the structure were tested over the following days, including the use of KNAUF Thermoboard Plus boards which have better thermal conductivity. Even after that there was no successful solution to the problem until the moment when the direct suspension system was exchanged for a spring-based one. The problem disappeared with this change, and over the next 8 weeks of operational testing it wasn´t noticed at all. This proved that the cause of the issue was the direct suspension system originally used to hang the CD profiles.

The reason was probably the thermal expansion of the suspended ceiling during heating. The warmth from the heating foils is transferred to the steel CD profiles via the plasterboards, and even though the temperature changes are not great, the expansion of the material cannot be ignored completely. While spring hangers enable the whole suspended ceiling to move to a certain degree via the swinging of the suspension wires, a structure hung via direct suspension is rigid. The pressure on the joints of the structure thus increased during heating - particularly on the edges of the suspended ceiling - and when the critical limit was exceeded, some of the CD profiles moved in the joints. These were almost microscopic shifts which, however, were enough to cause the crackling in various places described above. When cooling down, the CD profiles “returned” to their original positions, again accompanied by crackling noises.

Retrospectively, this cause appears to be logical and perhaps somewhat banal. However, we haven´t had any other similar complaints so far. Maybe installation companies - either consciously or by chance – preferentially use spring hangers for the installation of ceiling heating, and perhaps some customers whose ceilings do emit such noises accept this phenomenon thinking that it is a characteristic feature of ceiling heating. However, it was an unknown and unusual problem for us. It taught us a lesson which, among other things, resulted in the alteration of the mounting regulations for ECOFILM C heating foils in ceiling heating applications - spring suspensions are now needed for the hanging of plasterboard ceilings.