6
1.
Determine the total length of cable needed by adding the total roof edge
length (ft.) x feet of heating cable per foot of roof edge (see table below) roof
edge length x 0.5 (for the roof extension factor), the total gutter length (ft.) and
the total downspout length (ft. plus 1).
NOTE: The roof edge length (ft.) x feet of heating cable required per foot of roof edge equals the total roof
edge cable length required.
NOTE: The roof extension factor is the length of cable required to reach the cable in the gutter from the
roof edge.
2.
For shi
ngle roofs, add 1 foot (30 cm) of heating cable for each foot (30 cm)
of gutter.
3.
Add 1 foot (30 cm) of heating cable per foot (30 cm) of downspout.
4.
When the downspout is between the gutter ends, double the length of the
downspout to determine the length of cable needed.
5.
For roof valleys, measure the distance two thirds of the way up and double it.
Add this additional length to the overall cable length.
EXAMPLE (SHINGLE ROOF):
• Roof edge length: 15 ft. (with roof overhang of 1 ft.)
• Gutter length: 15 ft.
• Downspout length: 12 ft.
Length of heating cable required:
Roof edge length 15 ft. × 2 (see table) =
30 ft.
Gutter length
15 ft.
Roof extension
15 ft. x 0.5 =
7.5 ft.
Downspout length
12 ft. +1 =
13 ft.
Total
66 ft.
1
CABLE SELECTION
ROOF
OVERHANG
LENGTH
OF HEATING CABLE
CABLE LOOP
HEIGHT
SHINGLE ROOF
METAL ROOF
(24 IN. / 60 CM)
SHINGLE ROOF
METAL ROOF
None
1.9 ft / 58 cm
2.5 ft / 76 cm
18 in. / 46 cm
18 in. / 46 cm
12 in. / 30 cm
2.0 ft / 61 cm
2.5 ft / 76 cm
18 in. / 46 cm
24 in. / 60 cm
24 in. / 61 cm
2.7 ft / 82 cm
3.5 ft / 107 cm
30 in. / 76 cm
36 in. / 90 cm
36 in. / 91 cm
3.6 ft / 110 cm
4.5 ft / 137 cm
42 in. / 107 cm
48 in. / 122 cm
48 in. / 122 cm
4.5 ft / 137 cm
5.5 ft / 168 cm
54 in. / 137 cm
60 in. / 152 cm
