Roof gutters and downpipes
Heating cables are very suitable for ensuring snow and ice free gutters and downpipes. They prevent the formation of snow and ice lumps which can be very dangerous if they were to hit a person when falling from the roofs or roof gutters. Frost protection of roof gutters and downpipes is therefore a question of safety of people on the ground below. In addition, damaged roofs, gutters and downpipes after frost are avoided.
Roof projection / eaves
In cases of "warm" roofs, it may be necessary to install a heating cable on the roof surface, in the area above of the eaves, so as to prevent water for the melting snow to freezes again on its way to the gutter. Linear power of the cable should in the range 16-18W/m, and an area power of around 100W/m2 will suffice.
Planning and design
In a roof gutter, series resistant heating cables will normally be installed in a loop ("back-and-forth”), so that the linear power the heating cable must be half of the calculated linear power for the roof gutter installation. The highest permissible installed power in a roof gutter depends, amongst other things, on the material from which the gutter is made.
A self regulating heating cable adjusts the heat emission relative to the ambient temperature, which means that the cable will emit high power when it is covered by snow or ice. As snow or ice melt, the cable will decrease the output power, and if the temperature rises even more, the cable will reduce the power even further. Note however that a self regulating heating cable never "switches off", and that a temperature control system, or a simple switch-off option, is almost always necessary.
Using self regulating heating cables do not required any calculations. The only designs parameter to observe is that the specified maximum lengths for the heating cable in question are not exceeded.
The heating cable can lay in the roof gutter without any particular attachment or fixation, or it may be positioned, using special distance brackets in plastic, and hang freely in the downpipe (to the opening of the downpipe, or to frost free depth). The heating cable is suspended from the roof gutter edge, using a special suspension hook. On roofs, attachment must be carried out using equipment suitable for the roofing in question. On bitumen membrane roofs, the cable can be attached to the roofing using bituminous glue (or similar) but then the linear power shall not exceed 18W/m.
With a roof gutter thermostat for control and management of the heating cables, the energy efficiency of installed system is enhanced. Roof gutter thermostats ensure that the heating cables are only energized when moisture is detected and the current temperature may cause ice to form. This prevents unnecessary use of energy.
The heating cable is preferably controlled by a waterproof air thermostat, installed on a shaded side or part of the building. In “warm roofs”, where the temperature in e.g. the attic goes above freezing, due to poor insulation in the roof, a thermostat installed in the attic may be appropriate. This should switch on the heating cable system when the attic temperature reaches the point where snow on the roof begins to melt.
TXLP Single conductor heating cable
Single conductor heating cable (also called drum cable) is quite suitable for snow melting installations in roof gutters. Normally two strands of cable is installed in a gutter (one “loop”), which means that the "end" of the cable should come back to the starting point of the installation. This requires some calculations and planning of the installation. Single conductor heating cable systems should be calculated by a person possessing experience with such systems.
TXLP heating cable elements
TXLP heating cable elements (17W/m) is well suited for this application. Such a cable laid back-and-forth yields a linear power of 34W/m in the gutter, which is approved for both metal gutters and PVC gutters.
DEFROST PIPE self-regulating heating cables
DEFROST PIPE is a series of self regulating heating cables, where the DEFROST PIPE 20/GUTTER is particularly suitable for frost protection of roof gutters and downpipes. All variants of DEFROST PIPE can be cut length within the limitations set by Nexans and are thus very flexible in relation to varying roof gutter and downpipe -lengths. As a rule of thumb, it normally suffices to install one cable run in a gutter.
When using self-regulating heating cables, the power supply circuitry must be dimensioned with respect to the inrush current that may occur in such heating cables. Self regulating heating cable systems should be calculated by a person possessing experience with such systems.