Heat trace cable is the cheapest insurance against burst pipes, frozen well lines, and roof ice dams in Ontario. It is also the most quietly failing piece of electrical equipment on a typical cottage — installed once, forgotten, energized every winter, and ten years later it is the GFCI breaker that keeps tripping at -25°C. Here is what the OESC requires, what we install, and the failure mode that catches owners off guard every January.
Self-regulating vs constant-wattage: and what to install
Two technologies dominate the residential and cottage market:
- Self-regulating cable. A semiconductor matrix between two parallel conductors. As the cable warms, the matrix's resistance increases and current draw drops. As the cable cools, resistance drops and draw increases. The cable cannot overheat itself — it self-regulates by physics. Cuts to length on site without an end calculation. This is what we install on essentially every job. Brands: Raychem WinterGard, Heatline Self-Reg, Pentair Thermon.
- Constant-wattage cable. Resistance heating element of fixed length. Each kit is sized to a specific cable length. Cannot be cut. Can overheat if doubled-up or laid on itself. Older technology, still sold for specific applications but rarely the right choice for new residential work.
If you are buying a kit at a big-box store and it has a fixed length you cannot trim, it is constant-wattage. The kit will work, but it is less forgiving of installation errors.
What heat trace is installed on
- Exposed water lines — well lines from the well head to the house, supply lines in vented crawlspaces, lines run in unheated boathouses
- Drain lines in exposed locations, including ABS exposed in a cottage crawlspace
- Roof eaves and valleys on homes with ice-dam problems — the cable laid in a zigzag pattern on the eave shingles and in the valley creates a melt channel so meltwater from the warmer roof above can drain
- Downspouts and gutters at high-risk locations, often paired with the eave cable
- Septic lift station discharge lines from the tank to the field where the line runs above frost depth
OESC requirements: the rules that get missed
Heat trace cable in Ontario has specific code requirements that DIY installs routinely miss:
- Class A GFCI protection. All heat trace circuits must be on a Class A 5 mA GFCI device, either a GFCI breaker at the panel or a dedicated GFCI receptacle the cable plugs into. This is not optional. It is what catches the cable jacket damage we describe below before it becomes a fire.
- Dedicated branch circuit. Heat trace is typically on its own dedicated 15A or 20A circuit. Sharing the circuit with anything else means you cannot diagnose a GFCI trip cleanly.
- End seal and power-connection kit. The cold lead (the unheated tail that connects to power) and the end seal must be assembled with the manufacturer's kit. Wire nuts and electrical tape are not legal terminations on heat trace cable, full stop.
- Cable installed per manufacturer's instructions. Sounds like boilerplate; matters in practice. Self-regulating cable wrapped at the wrong pitch around a pipe, or doubled-back on itself in violation of the install guide, voids warranty and creates hot spots.
- Insulation over the cable. Pipe-protection heat trace is almost always installed under pipe insulation. The insulation is part of the system — it keeps the heat at the pipe instead of radiating to the crawlspace.
The failure mode nobody warns you about
Self-regulating cable has a real end-of-life. The polymer matrix between the conductors degrades with thermal cycling and UV exposure (for exposed roof installations). The failure does not look like "the cable stops working." It looks like this:
- Cable performs normally for the first 7–8 winters.
- In year 9 or 10, the GFCI starts tripping during the first cold snap of the year.
- Owner resets the breaker. It holds for a few days.
- Next cold snap, the GFCI trips again.
- By the third cycle, the GFCI trips within minutes of being reset.
What is happening: the cable jacket has hairline cracks, water from condensation under the pipe insulation is reaching the conductors, and the leakage current is climbing as the cracking progresses. The GFCI is doing its job — telling you the cable is unsafe. The fix is not to bypass the GFCI; the fix is to replace the cable.
The honest rule of thumb: self-regulating heat trace cable in Ontario service is a 7–12 year part. If your cable was installed before 2017 and you have not replaced it, plan for a replacement in the next two seasons. If the GFCI is already tripping, replace this year — before you wake up to a burst pipe.
Eaves and valleys vs pipes: different problems, different installations
Pipe-protection heat trace is straightforward: cable run along the pipe, end-sealed, insulated over. Roof and eave heat trace is more involved and harder to do well.
- The cable needs to be laid in a zigzag pattern across the eave that creates a continuous melt channel — typically a 16-inch zigzag with the loops clipped to the shingle
- The cable needs to extend up into the valley and follow the valley line
- The cable needs to extend down through the gutter and into the downspout to the ground line — otherwise the meltwater refreezes at the bottom and the channel backs up
- Roof heat trace clipping requires shingle clips that do not penetrate shingles (no nails, no screws) — slide-under clips that grip without holes
The DIY job we see most often missed: cable on the eave but not in the downspout. The eave melts, the meltwater runs to the gutter, the gutter is cold, the meltwater refreezes, and within a day you have a frozen waterfall down the side of the house with no path to the ground. The cable has to make a continuous path from the warm roof to the ground.
Control options: thermostat vs always-on
Self-regulating cable does not strictly need a thermostat — physics regulates the output. But adding a thermostat or controller saves real money on electricity:
- Ambient thermostat (Raychem AMC-1A, Pentair Auto-Trace) — energizes the cable when outdoor temperature drops below a setpoint (typically +5°C). Off above the setpoint. Saves the cable from running needlessly in the +10°C shoulder-season days.
- Snow-sensing controller — adds moisture detection on top of temperature. Energizes only when it is cold AND wet (actively snowing or melting). More savings, especially for roof systems. Brands: EasyHeat Pro Snow Melting Control, Tekmar 654.
- Always-on with internal regulation — the cable plugged into a GFCI-protected receptacle on a switched circuit that the owner energizes in fall and de-energizes in spring. Simple, reliable, slightly more electricity used.
When to call us
If you have heat trace that is tripping the GFCI, heat trace approaching 10 years old that has not been inspected, or you are planning a new install for a pipe or roof at risk, we do residential electrical work across both clusters with heat trace as a regular fall scope. The companion piece on cottage closing covers the fall test you should do on every heat trace circuit. Request a heat trace quote and we will scope it before the first freeze.