By Peter Leal
Heating cables an effective solution for de-icing.
By Peter Leal
Heating cables are commonly referred to as heat trace cables, heat tracing, or heat tape. The most advanced cable design, self-regulating heating cables, are also known as self-limiting cables.
Whatever they are called, all work largely on the same principle: when voltage is applied across a length of wire of a given resistance, it then dissipates a fixed level of power in the form of radiating heat based on Ohms law. Heat is emitted due to the resistance in the cable alloys as the current moves through it, thereby warming up the immediate physical surroundings.
For that reason, heating cables are used in a multitude of applications, from pipe freeze protection; to snow melting on a sidewalk or driveway; to preventing ice dams on roofs; to keeping dangerous icicles from forming in gutters and downspouts; to indoor floor warming when installed under tiles or hardwood floors. In addition, heating cables are used in a range of industrial freeze-protection and process-maintenance applications to keep liquids in pipes at a constant temperature to prevent degradation of the liquid or to maintain viscosity for flow conditions. Industrial heating cables will not be addressed in this article.
Constant-wattage heating cables are the most basic of the two. These types of fixed-length cables are either on at full 100 per cent heat output or off at zero heat output. They usually require a thermostat to maintain a constant temperature. Constant-wattage cable cannot be overlapped, as this could cause it to overheat. A break in a section of cable will cause a complete failure of the entire system. They offer the advantage of being inexpensive but cannot be cut on site. Instead, they are sold in specific lengths and wattage outputs, making them less versatile than self-regulating cables. Constant-wattage cable can be used on indoor and outdoor water supply lines that are subject to freezing temperatures. They are ideal for use in crawlspaces, cottages, barns and outbuildings that are not regularly heated.
Self-regulating heating cables overcome the constrictions of constant-wattage cables. In this type of cable, the electrical power wires are co-extruded into a heating element consisting of a polymer-based material with carbon particles. This provides a resistance path, hence a circuit along the length of the heating cable. This resistance, and therefore the output of the heating cable, varies depending upon the temperature due to microscopic expansion and contraction of the polymer. Power output is reduced as temperature increases. Conversely, at lower temperatures, the power is increased. No thermostat is required because they automatically vary their heat output based on changes in the surrounding temperature. Designed for industrial, commercial and residential applications, they deliver maximum freeze protection and temperature maintenance, plus they can be cut to any length on site quickly and easily. Because they are designed to vary heat output as the surrounding temperature changes, they are ideal for use on metal or plastic water supply and drain pipe applications that are subject to freezing temperatures, for processing applications where piped liquids require a constant temperature, and as freeze protection for branch sprinkler systems.
Consider this: a volume of water, when frozen, will expand to nine per cent greater than original. So it is no surprise that a fully or partially frozen pipe will swell up and crack, in particular when there is air trapped in it.
A bulge or crack in a pipe with ice seeping out is a clear indication of a burst pipe. Occasionally, however, the pipe may look fine and a homeowner may not see the small fractures caused by ice expansion. Unfortunately, once the ice inside a frozen pipe begins to melt and water seeps out, it is already too late. Depending on the extent of the damage, total cleanup costs from a burst pipe can soar to tens of thousands of dollars. State Farm Insurance estimates the average insurance claim for water damage from frozen pipes is approximately $15,000.
If a building owner knows that a certain part of a structure with active water pipes may experience temperatures below freezing, the smart solution is to install a heating cable. When combined with an integrated thermostat, the system is automatically turned on when temperatures drop below freezing. The cables provide the needed level of heat to keep the pipes from freezing but not enough to heat the water inside the pipes. The thermostat provides automatic control of the system so it saves energy by powering the cable only when required. For optimal performance of the system, pipe insulation can be installed over the cable to help retain heat, and plastic pipes can be wrapped in aluminum foil so the heat is dissipated evenly in the pipe
The benefit of this design is that the cables are installed once and left mounted on pipes for years — even when temperatures drop as low as minus 40 C.
PREVENTING ICE DAMS
An ice dam is a formation of ice that appears at the eaves of a roof during extended periods of snow and cold weather. Ice dams form when ice builds up along the edge of the roof, creating a dam that traps water in a pool. If a large enough amount of water collects, it can force its way underneath the roof shingles and all the way into a building, causing extensive damage to ceilings, floors and behind walls. Repairing a roof is expensive. Even a minor repair as small as a couple square feet typically costs $1,000 or more. Larger repairs, or slate and metal roof repairs, can costs thousands more. A complete re-roof, meaning tearing off the old roof from the house and replacing it with a new one, can range in cost from $4,000 up to $25,000.
Again, the proven solution to roof and gutter de-icing are heating cables. By preventing ice dam formation along roof edges, in gutters, drains and downspouts, the cables create a path for melted water off the roof that prevents ice dams from forming. An automatic controller, included with most systems, makes operation more energy-efficient. By connecting the controller between the electric outlet and the cable, the controller will turn the system on when temperatures are below three degrees and there is a presence of water on the sensor’s surface. If only one of the above-mentioned conditions exists, the control will not activate the system. When the temperature rises above nine degrees, the controller turns the system off.
Heating cables can be installed underneath concrete or asphalt driveways, sidewalks or patios to fight off snow or ice. This is a much more efficient and green alternative to shoveling or applying environmentally harmful salt. Formed into mats of varying sizes, the heating cable system is applied underneath the concrete or asphalt surface area or pavers. The mats are extremely cost-effective and eliminate the expensive, labour-intensive hassles of snow removal by automatically maintaining a surface temperature above freezing. Two conditions must be present concurrently for the mats to activate: the temperature must be freezing and the system must detect moisture or snowfall. Even in Canadian cities, the actual time of snowfall to the ground is under 30 hours per year. From a cost standpoint, that translates to just a few dollars per year. It also means no more calling costly snowplow services that can range into hundreds or even thousands of dollars per year. Plus, if it snows in the middle of the night, the homeowner will wake up to an already cleared sidewalk and driveway – unlike their neighbours. Another less obvious advantage is that the mats are noiseless. Anyone who has had to listen to a snowblower operating in the wee hours of the morning will appreciate this.
In most cases, snow will melt at a rate that keeps up with average snowfall, minimizing accumulation of snow on the heated surface. Depending on the voltage available and the configuration, the mats can easily be combined and tailored to cover a unique walk, stair, patio and driveway layout.
Businesses and homeowners benefit from safer walkways, lower insurance rates and compliance with regulations for disabled access. Loading docks, ambulance entries and passenger platforms at transportation depots also benefit from this protection where pedestrians can move securely on the protected surface.
Hardwood and tile floors can feel uncomfortably cold even in warm climates. Under-floor warming cables remove the chill with gentle, continuous warmth when used as supplemental heat to make the floor cozy, or as space heat to warm an entire room. Depending on the manufacturer, systems can be used with numerous choices in surfaces including ceramic, porcelain, terrazzo, glass mosaic, marble and natural stone and agglomerates, as well as under engineered wood and laminate. Cables can even be installed in tiled showers or other wet areas, although it is recommended that the homeowner check with their local electrical inspector first to verify that this application is allowed in the jurisdiction.
Besides comfort, floor-warming systems are safe, energy-efficient and economical. Once installed, it’s nearly impossible to damage or cut the cables. In addition, a GFCI-protected programmable thermostat will instantly cut power in the event of a short. The thermostat also offers precise temperature control, monitoring and regulating the floor temperature to provide the optimal warmth. Cost is minimal: at 12 watts per square foot, a 30-square-foot mat draws the equivalent of an electric blanket. Plus, it is estimated that adding floor warming throughout a home can increase its resale value by as much as four per cent.
Modern floor-warming systems are manufactured as either free-form cables that provide maximum design versatility, or in fixed cable mats for labour savings in standard-shaped rooms.
Free-form cables are loose, so they can be turned and positioned in any pattern to fit areas with curves, angles or obstacles. The cable spacing is not fixed and it is recommended that a two- to three-inch gap be maintained between them. It is also highly recommended to create a buffer area on the floor plan, where heating is not essential and which can be used to run leftover cable. While it is common practice, duct tape is not recommended for securing cables since it does not guarantee proper spacing and may result in insufficient or leftover cable lengths and uneven heat output. Instead, free-form cables should be installed using clips or uncoupling membranes directly onto the subfloor structure, and are then embedded in thin-set or a self-leveling underlayment.
As you would expect, fixed-cable installation is a faster, less labour-intensive process than free-form cables. Self-adhesive-mat floor warming systems are even easier. The mats are commercially available in standard sizes of pre-fabricated rectangular mats with a self-adhesive, wide-spaced backing to help reduce installation time and labour. The mats can be placed on the substrate and will stay put while the mat is embedded in thin-set or a self-leveling underlayment. At less than 1/8-inch thick, the mats result in virtually no floor height buildup, significantly reducing retrofit costs since the door or trim work does not need to be raised.
Peter K. Leal, is product marketing manager for Emerson, and has been with Emerson for eight years. He has responsibility for all EasyHeat branded products, which includes heating cables and thermostats. He has a degree in industrial engineering and has over 20 years experience in product management and new product development, along with over 10 years experience in the consumer/retail market.