Heat tape used on roofs and gutters is properly called heat cable. Heat tape is an insulated electrical wire that can be applied to water pipes to keep them from freezing and bursting. Heat cable is a similar product but is designed for installation along your roof's edge to prevent ice buildup along the eaves and inside the gutters. Heat cable is easy to install and can help prevent ice dams and freezing inside gutters and downspouts.
What Are Ice Dams?
Each winter, ice dams building up along roof overhangs cause damaging leaks inside many hundreds of homes. Ice dams occur because snow and ice on the roof melts from interior heat, travels down the roof and freezes again as it reaches the exposed overhangs or eaves. Over time, this frozen melt-off builds up into a dam barrier that causes ice and water to back up under the shingles, causing damage interior ceiling and wall surfaces. And the sheer weight of ice dams can damage the roof overhangs and gutters.
If heat cable is installed incorrectly or if the wrong type of product is used, it could create a fire or electrical shock hazard. This is also true for heat cable that is old and deteriorated. If your home has heat cable that has been installed before you moved in or is more than five years old, it is a good idea to have it checked for proper function, or simply to replace the old cable with a new cable.
Heat cable is sold in a variety of lengths, ranging from 30 to 200 feet. Cables have 3-prong grounded plugs for plugging directly into outdoor electrical outlets. Do not use heat cables with extension cords. Make sure the heat tape you use is UL-listed, indicating that it has been tested by Underwriter's Laboratories. Manufacturers that avoid UL listing usually offer substandard products that are more likely to fail than their listed counterparts.
Installing Heat Tape
Note: Heat cables must be plugged into a GFCI (ground-fault circuit-interrupter) outlet, for safety. If your outdoor outlet is not GFCI-protected, it's easy to replace it with a new GFCI outlet. Here are the basic steps for installing new heat cable along a roof eave and gutter:
- Determine the length of heat cable you need. First, measure the perimeter of your roof line. Then, measure the depth of the eave overhang, measuring from the edge of the roof (not the gutter) straight back to the outside wall. If the eave is 12 inches deep, multiply the roof-line measurement by 4. If the eave is up to 24 inches deep, multiply the roof-line measurement by 5.3. If the eave depth is up to 36 inches, multiply the roof-line measurement by 6.8.
Measure the length of each downspout and add it to the roof-line total. If a downspout is not at the end of a cable run, double its measurement (because the cable will go all the way down and back up inside the downspout).
Measure the distance between the edge of the roof (where you will start the heat cable) and the electrical outlet where you will plug in the cable. Add up all of the dimensions; this is the length of cable you need.
- Route the cable from the electrical outlet to the starting point on the roof. Clip the starting point of the cable to a shingle that is a little bit farther up the roof than the outside wall; this ensures the cable will warm the entire depth of the roof overhang. Secure the cable to the shingle with one of the provided cable clips.
- Run the cable down to the gutter at an angle and form it into a loop, using one of the provided eave clips; attach the clip to the bottom edge of the shingle. The cable should form a loop that extends partway into the gutter.
- Run the cable back up the roof in a zig-zag pattern, creating a triangular shape that is about 15 inches wide. Bend the cable at the top of the triangle and secure it to a shingle with the shingle clip.
- Repeat the same zig-zag pattern as many times as needed to cover the entire perimeter of the roof.
- Begin laying the cable into the gutter once you've reached the end of the roof run. Secure the cable to the gutter clips you installed at the roof's edge, using the provided hooks or clips. The cable portion of the gutter hooks onto the loops of the cable on the roof.
- Feed the cable as a loop into any intermediate downspouts, extending the loop all the way down to the downspout outlet.
- Continue installing the gutter cable back to the cable's starting point, then thread the end of the cable down through the downspout to the downspout outlet.
- Plug the cable into the GFCI outlet and make sure it is working properly. Unplug the cable and leave it unplugged until it begins snowing. There is no need to keep the cable plugged in if there is no snow or ice on the roof.